A Geometric Morphometric Analysis of Ruminant (Ungulata: … · 2015-12-04 · 2 Figures and Tables [10] Figure 1 - Mean shape and range envelopes of browsing, grazing, and intermediate

A Geometric Morphometric Analysis

of Ruminant (Ungulata: Artiodactyla)

and Ornithopod (Dinosauria:

Ornithischia) Snouts: Comparative

and Functional Ecomorphology

A report submitted in partial fulfilment of the requirements for the

degree of MSc Advanced Methods in Taxonomy and Biodiversity,

Imperial College London and Natural History Museum, London

Jonathan Tennant 00661116

Natural History Museum Cromwell Road

London SW7 5BD

1

Contents

[4] 1. 0 Abstract

[5] 2. 0 Introduction

[6] 2.1 Previous Attempts to Infer Feeding Strategy from Morphology

[12] 3.0 Materials and Methods

[20] 4.0 Results

[20] 4.1 Procrustes Superimposition

[21] 4.2 Ecological Classification

[28] 4.3 Taxonomic Classification

[34] 4.4 Shape Classification

[58] 5.0 Discussion

[63] 6.0 Conclusions

[66] 7.0 Acknowledgements

[67] 8.0 References

[83] 9.0 Appendices

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Figures and Tables

[10] Figure 1 - Mean shape and range envelopes of browsing, grazing, and intermediate

ruminants (modified from Solounias et al., 1988)

[13] Figure 2 - Exemplar ruminant profile shapes

[14] Figure 3 - Grid plot of Corythosaurus casuarius specimens in Procrustes-scaled space

[20] Figure 4 - Procrustes-scaled mean shape and overlay plot for all ruminant specimens

[20] Figure 5 - Procrustes-scaled mean shape and overlay plot for all ornithopod specimens

[22] Figure 6 - Two-dimensional PCA score plot for ruminants classified according to their

feeding type

[23] Figure 7 - Three-dimensional PCA score plot for ruminants classified according to their

feeding type

[24] Figure 8 - Two-dimensional CVA score plot for ruminants classified according to their

feeding type

[24] Figure 9 - Three-dimensional CVA score plot for ruminants classified according to their

feeding type

[25] Figure 10 - Modelled CVA axes in two-dimensional CVA space for ruminants classified

according to their feeding type

[26] Figure 11 - Back-projection of modelled CVA axes into two-dimensional PCA space

[27] Figure 12 - Χ2 probability density function plot for ruminants classified according to

feeding type in CVA space

[27] Figure 13 - Strobe plot of modelled CVA axes in PCA space for ruminants classified

according to feeding type


family


family


sub-family


sub-family


family


family

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sub-family


sub-family

[34] Figure 22 - Two-dimensional PCA score plot for ruminants classified according to the

primary shape descriptor (‘blunt’ or ‘pointed’)

[35] Figure 23 - Three-dimensional PCA score plot for ruminants classified according to the

primary shape descriptor

[36] Figure 24 - Two-dimensional CVA score plot for ruminants classified according to the


[37] Figure 25 - Two-dimensional PCA score plot for ruminants classified according to the

secondary shape descriptor (‘pointed’ and ‘blunt’ appended with either ‘concave’, ‘convex’

or ‘linear’)

[37] Figure 26 - Three-dimensional PCA score plot for ruminants classified according to the

secondary shape descriptor



[39] Figure 28 - Strobe plot of modelled CVA axis in PCA space for ruminants classified

according to the primary shape descriptor

[39] Figure 29 - Strobe plot of modelled CVA axes in PCA space for ruminants classified

according to the secondary shape descriptor

[42] Figure 30 -Projection of the ornithopod PCA scores into the PCA space defined by PC-1

and PC-2 for the ruminants when classified according to feeding type

[43] Figure 31 - Projection of the ornithopod PCA scores when classified according to their

family into the PCA space defined by PC-1 and PC-2 for the ruminants when classified

according to feeding type

[44] Figure 32 - Two-dimensional PCA score plot for ornithopods when classified according

to their family

[45] Figure 33 - Two-dimensional CVA score plot for ornithopods classified according to

their family

[46] Figure 34 - Two-dimensional CVA score plot for ornithopods classified according to

their chronostratigraphic age

[47] Figure 35 - Back-projection of modelled CVA axes into two-dimensional PCA space for

ornithopods classified according to their chronostratigraphic age

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[48] Figure 36 - Strobe plot of modelled CVA axes in PCA space for ornithopods classified

according to their chronostratigraphic age

[50] Figure 37 - Two-dimensional PCA score plot for ornithopods classified according to the


[50] Figure 38 - Three-dimensional PCA score plot for ornithopods classified according to

the primary shape descriptor



[52] Figure 40 - Two-dimensional PCA score plot for ornithopods classified according to the


[53] Figure 41 - Two-dimensional CVA score plot for ornithopods when classified according

to the secondary shape descriptor

[54] Figure 42 - Back-projection of modelled CVA axis into two-dimensional PCA space for

ornithopods classified according to the primary shape descriptor

[54] Figure 43 - Strobe plot of modelled CVA axis in PCA space for ornithopods classified

according to the primary shape descriptor

[55] Figure 44 - Strobe plot of modelled CVA axes in PCA space for ornithopods classified

according to the secondary shape descriptor

[21] Table 1 – Calculated principal component eigenvalues for both the ruminant and

ornithopod Procrustes-transformed data sets

[40] Table 2 - Results of the chi-squared likelihood ratio test for all ruminant groups

[47] Table 3 - Results of the chi-squared likelihood ratio test for all ornithopod groups

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Abstract

Snout shape is a prominent aspect of herbivore ecology with respect to feeding strategy,

affecting both forage selectivity and intake rate. Within ruminants, feeding classes are

delimited based on snout shape, with grazing species attributed ‘blunt’ snouts and

browsing species ‘pointed’ snouts. These functional varieties have yet to be tested in a

robust and quantifiable structure. In this study, using a variety of geometric morphometric

techniques, this aspect of functional ecology is analysed in a statistically rigorous geometry-

based framework, principally testing to see if feeding strategy is consistent with snout

morphology and using a two-dimensional profile of the premaxilla in ventral aspect as a

proxy. The secondary objective is to assess this approach using ornithopod dinosaurs, the

putative extinct analogues of modern ruminants, to see whether similar patterns in shape

variation can reveal their feeding strategies. The results here reveal that when ruminants

are classified ecologically based on a priori assigned feeding strategies, they cannot be

discriminated on the basis of their premaxilla shape profile, instead forming a shape

variation continuum. Moreover, previously used terminology such as ‘pointed’ and ‘blunt’

are deemed inadequate for delimiting snout shape varieties, also lacking the descriptive

power to define the morphological disparity demonstrated. These results are statistically

significant, and found not to be an artefact of phylogenetic similarity. Conversely,

ornithopods are found to exhibit a strong shape variation pattern between ‘blunt’ and

‘pointed’ snout shapes. These patterns exist in both a phylogenetic and temporal context,

and may relate to both browsing height and forage selectivity as has been previously

proposed for diplodocoid sauropods. The pattern shows a trend from a plesiomorphic

selective ‘browsing’ condition in the Jurassic and Lower Cretaceous for many clades,

through a transitional experimental phase with iguanodontids in the Lower Cretaceous,

culminating in the large-bodied hadrosaurs in the Upper Cretaceous, which have

distinctively flat and laterally-widened snouts for non-selective, ground-level ‘grazing’. This

transformation is proposed to be related to increased nutritional requirements relating to a

systematic increase in body size, and possibly associated with increased angiosperm

diversity during the Upper Cretaceous.

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2.0 Introduction

The idea that ungulates and ornithopods may be comparable in terms of ecological and

macroevolutionary significance has long been of interest (Dodson, 1975; Molnar, 1977;

Weishampel, 1985; Norman and Weishampel, 1985; Carrano et al., 1999; Rybczynski et al.,

2008). Parallels have been drawn in the context of their sexual dimorphism, masticatory

apparatus and cranial kinetics, herding, and parental care (Carrano et al., 1999), as well as

with their digestive systems (Farlow, 1987). Within ungulates, it is often claimed that snout

morphology performs an integral role in both defining various ecological guilds, as well as

playing a significant interactive role during ingestion. However, the claim that there is a

close association between snout morphology and feeding strategy has not been subjected

to a rigorous, geometry-based quantitative analysis to date. The proximate target of the

present investigation is a determination of whether the shape of the premaxilla can be used

to delimit feeding strategies successfully in ruminants, and then whether the same patterns

can be used to make inferences about the feeding habits of their apparent extant

analogues, the ornithopod dinosaurs. This question is examined within a geometric

morphometric framework, due to its inherent analytical strength when studying the shape

of morphological structures.

Members of the Suborder Ruminantia (Order Artiodactyla) are a clade of even-toed

ungulate mammals defined uniquely by possession of a two-step digestion system involving

the fermentation chamber in the foregut of the stomach, and by the presence of a

reticulorumen, the structure from which the clade takes its name. This Suborder includes

many well-known ungulate taxa including antelope, deer, giraffe, and cattle, together

occupying and regulating many modern terrestrial ecosystems. Currently some 200 extant

species are recognised (Fernández and Vrba, 2005). Ornithopods (Order: Ornithischia)

exhibit a temporal phylogenetic hierarchy, with camptosaurs and dryosaurs occupying the

Late Jurassic, iguanodontid forms and hypsilophodont-grade taxa dominating the Lower

Cretaceous, and hadrosaurids radiating in the Upper Cretaceous. This correlates to a

systematic increase in body mass, as well as masticatory complexity through time. Along

with then contemporaneous sauropods, they formed a major constituent of Mesozoic

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terrestrial communities, dominating herbivorous niches until their extinction during the

end-Cretaceous mass extinction.

Ruminant feeding strategies are reflected in their craniodental and gastrointestinal

morphophysiological diversity, and have been conventionally categorised into ‘browsers’

and ‘grazers’, with an ‘intermediate’ sub-group, where browsers are considered to be

obligate non-grazers, but not vice-versa (Clauss et al., 2003). For example, Bodmer (1990),

Mendoza et al. (2002) and Gordon (2003) include variants of frugivores, high-level

browsers, and fresh grass grazers in this group in an attempt to encapsulate the full

theoretical range of feeding strategies. Variations in feeding strategy also explicitly occur in

a spatiotemporal context. These relate to the ‘environmental stresses’ of Bourtière and

Hadley (1970) and plausibly a hierarchical grazing succession related to species’ migration

patterns, geomorphology, resource partitioning or forage quality (Gwynne and Bell, 1968;

Fryxell, 1991; Voeten and Prins, 1999). No attempt to classify their putative ornithopodan

analogues in such a manner has been undertaken to date.

2.1 Previous Attempts to Infer Feeding Strategy from Morphology

Van Zyl (1965) was the first to define a classification for ungulates explicitly based on

feeding strategy. Following this, Hofmann and Stewart (1972) and Hofmann (1973, 1988,

1989, 1991, and 1999) extended Van Zyl’s definitions to contain a morphophysiological

underpinning, specifically in ruminants pertaining to their particular ecological roles. This

modified feeding classification scheme has maintained its value ever since based on its

heuristic value. Its popularity is nevertheless somewhat counter-intuitive insofar as, until

recently, few studies attempted to empirically or theoretically validate these initial putative

classifications (Clauss et al., 2008b).

The typical dichotomy of ‘browsers’ and ‘grazers’ relies on a botanical foundation. Browsers

typically consume berries and dicotyledonous leaves (e.g., Hofmann and Stewart, 1972;

Jarman, 1974; Janis, 1995). Grazers consume monocotyledonous grasses, and intermediate

feeders vary depending on season and geography (e.g., Shipley, 1999; Sanson, 2006). The

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significance of this variation is that the physio-mechanical and biochemical properties of

the different plant types are adequate to potentially drive this functional dichotomy in

ruminants. Clauss et al. (2003) argued convincingly that the properties of respective forages

exert strong control on the evolution of the masticatory apparatus and gastrointestinal

tract; specifically the reticulorumen physiology within ruminants (see also Clauss et al.,

2010).

The botanical definitions of browsers and grazers have a complicated history, with various

authors unable to settle on a consistent threshold of forage consumption for either class.

Janis and Ehrhardt (1988), Janis (1990), Janis et al. (2000) and Pérez-Barbería et al. (2001a)

regarded browsers as ruminants that consume <10% grass, and grazers as those consuming

>90% grass per annum, with all other species being ranked as intermediate. These authors

provide no justification for these seemingly arbitrary thresholds. Conversely, Gordon and

Illius (1996), Pérez-Barbería and Gordon (1999), Pérez-Barbería et al. (2001b) and Mendoza

et al. (2002) selected >75% grass per annum as the threshold criterion for their grazer class,

and >75% browse for browsers. There is further confusion, as Clauss et al. (2009a) defined

grazers as those consuming >80% monocot material, and strict browsers as those with a

“very low intake of monocot forage” (p. 399), whilst others use natural diet as a continuous

variable (e.g., Sponheimer et al., 2003). This variation is partially summarised in Clauss et al.

(2008b). In many other studies, feeding strategy delimitation is purely qualitative (e.g.,

Owen-Smith, 1997), where grazers are classified as those “consuming primarily grasses,

sedges and other graminoids”, (p. 178). Gordon and Illius (1994) find that different

thresholds of classification give different results in ecological analyses. Defining these

thresholds in congruence with functional or ecological significance remains a problematic

issue.

There are numerous morphophysiological parameters affecting digestive rate and

efficiency, as well as masticatory efficiency. However, the first part of an organism to

interact with forage (excluding perhaps the tongue and prehensile lips) is the snout. Snout

shape is a highly prominent aspect of herbivore ecology, defining initial intake rate,

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chewing efficiency and forage selection ability (Gordon and Illius, 1988; Murray and Brown,

1993; Shipley et al., 1994; Pérez-Barbería and Gordon, 1998; Clauss et al., 2007).

The anterior section of the snout is predominantly formed by the premaxillae, the shape of

which is an important ecomorphological feature, or trait. It is commonly noted that

browser mammal species have pointed premaxillae and grazers a more squared or blunt

shape representing the derived cropping condition (e.g., Janis and Ehrhardt, 1998; Pérez-

Barbería and Gordon, 2001). Intermediate feeding strategies have an intermediate form,

often mediolaterally compressed into a club-like shape (Solounias and Moelleken, 1993).

The functional significance of snout shape lies in selectivity; i.e. a more pointed rostrum

allows for increased selection sensitivity, whereas a wider or blunter form confers a more

random cropping process, with greater oral intake (Gordon and Illius, 1988; Janis and

Ehrhardt, 1998). Following this, Janis et al. (2010) inferred that, theoretically, a higher

intake rate should drive covariation within the mandible, forcing the evolution of stronger

anatomical structures (strengthening or fusion of sutures, increased muscle attachment

area, and decreasing pleurokinesis and resistance to strain). This should not be taken to

suggest that, as snout shape varies, it forces covariation of other morphophysiological

parameters. Rather, it simply controls the initial parameter with which all other domains

interact. Janis et al. (2010)’s suggestion was corroborated by Fletcher et al. (2010), who

determined that evolution of the masticatory apparatus has a functional or adaptational

origin, challenging other studies where it is deemed to be a phylogenetic artefact (e.g.

Pérez-Barbería and Gordon, 1999, 2001; Figuerido et al., 2010; Raia et al., 2010).

Irrespective of these process-level speculations and investigations, the functional varieties

of snout shape in ruminants have yet to be tested in a robust quantifiable framework

beyond simple exemplar outlines. Solounias et al. (1988) and Solounias and Moelleken

(1993), following the methodology of Walker (1984), used snout shape primarily to aid

reconstruction of palaeodiets in ruminants. Their assessment is based on a quantitative

interpretation of exemplar taxa, with the method requiring construction of the anterior

snout curve using a cubic spline-fit function framed to assess intraspecific variation. The

construction method uses a somewhat arbitrary system of vectors to encapsulate the

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majority of premaxillary shape variation. These authors use photographs in dorsal aspect

stating that there is “no homologous point” on the premaxillary outline (Solounias and

Moelleken, 1993; p. 1063). This is why the ventral aspect should be preferred, due to the

easily traceable premaxillary-maxillary suture, and the fact that this is the interactive

surface of the oral aperture. The main drawback with their method is that the a priori

classification of specimens into functional feeding guilds - with no statistical testing or

evidence-based support for assignment - will clearly exert a degree of subjectivity in the

mean shape and shape variation envelopes. Classification should ideally be determined a

posteriori, once distinct variations between sub-groups has been discovered, if it all. For

example, in Figure 3 of Solounias et al. (1988), the intermediate shape looks considerably

closer to the grazer class (not ‘half-way’, as stated; Fig. 1). This highlights the problem of

independent author bias whenever a rudimentary qualitative method of discrimination is

applied. The images depicted only serve to emphasize the imprecision of already arbitrarily

bound categories, and the mean shapes are not a useful guide due to the overlapping

shape range envelopes. The statistics provided in Table 1 of Solounias et al. (1988)

confounds matters further, as their ‘intermediate’ forms are clearly more similar to grazers.

Janis and Ehrhardt (1988) and Gordon and Illius (1988) posit snout width as a proxy for

distal snout shape, with measurements taken at the ventral maxilla-premaxilla intersection

on the lateral margin. When describing the geometry of complex shapes, it is usually

inadequate to attempt to describe shape with a single linear metric, as equal

measurements can often describe completely disparate geometries of varying complexity.

These authors used this measurement, and the palatal width to define a ‘relative muzzle

width ratio’, which they used to represent the ratio between body size and the oral

aperture, as well as possibly representing oral intake and processing rate (note, that

‘muzzle’ describes the flesh covering the snout, not the cranial bones, as misconstrued

here). A ratio is a poor measure of shape when used singularly, since all the simplest shape

a ratio can represent is an ellipse, if the two measurements represent orthogonal axes, as in

the method used. This may be adequate for partially representing extremes of the

‘browser’ end of the continuum, but can just as easily describe a blunt form, as grazers are

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postulated to have. In fact, the shape a ratio can represent can be infinitely complex. For

example, imagine trying to model a sine-wave with a two-dimensional ratio! Hence ratios

are completely inappropriate proxies for snout shape (contra Janis and Ehrhardt, 1988).

Furthermore, ratios will also almost always fail to account for the ubiquity of allometric

growth patterns in organisms. Their results however, did find a general relationship

between muzzle width and the defined dietary categories. Nevertheless, these authors

failed to account for phylogeny, despite acknowledging that phylogenetic affinity may

constrain morphological design in terms of cranial plasticity, based on the general

presumption that organisms with closer shared ancestry are more likely to have increased

morphological similarity.

It is apparent that many underlying hypotheses regarding the browser-grazer dichotomy

have been rejected based on insufficient data, a lack of statistical support, or simply

correction based on more recent analysis (see Gordon and Illius, 1994, and Robbins et al.,

1995). However, Codron et al. (2007) reject the results of both of these studies, due to the

over-simplification of the biomechanical properties of associated plants. Alternatively,

Codron et al. (2007) suggested that dietary variation occurs on a spatiotemporal scale for

all browsers and grazers, and retains an intraspecific signal, conforming to Owen-Smith

(1997) and du Toit (2003).

In phylogenetic analysis, estimated cladograms are typically rejected without consideration

if no methods of statistical support are applied, in the context of sensitivity to data

Figure 1 – The mean shape (dark lines) and range envelopes (stippled area) of the anterior snout in

browsing, intermediate and grazing ruminants, modified from Solounias et al. (1988). The numbers

indicate the number of species used for the reconstructions.

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perturbation or decay tests. Ecological hypotheses clearly require similar scrutiny, given the

availability and ease of application of numerous relevant statistical procedures. In spite of

this, several distinctions are becoming apparent between browsing and grazing ruminants,

and are supported within a statistical framework (e.g., Clauss et al., 2008b). Note that, in

this context, support is not synonymous with accuracy. In the respect of the underlying

signals being recovered, support describes results that can be maintained and replicated

with high explanatory power, as revealed by statistical analysis, given the precision of the

underlying data.

The history of ecological classification in ruminants is convoluted, with only marginal

progress in the way of clarity or consensus. Based initially on a simple botanical

underpinning, the problem became increasingly multifaceted as new functional traits were

exposed with new methods of analysing them, and new theoretical revisions. This problem

can be framed as, what, if any, is the best method of classifying ruminants in a functional

ecological context, and what will be the traits that define these discrete categories. The

principle aim of this study, then, is to determine whether snout shape varieties can be

supported in a formally statistical framework using geometric morphometrics, with defined

morphotypes covarying between feeding strategies. If it can be demonstrated that snout

shape does not affect feeding strategy in ruminants, a secondary objective will be to further

test this approach on ornithopod dinosaurs to determine whether similar patterns of shape

variation – that might reflect feeding strategy – are evident.

The null hypothesis for this investigation relates to the conclusions of Pérez-Barbería and

Gordon (1999), among others, that feeding strategy is incongruent with premaxilla

morphology. The alternative hypothesis is that the shape of specimen snouts will form a

continuum, with ‘browser-type’ and ‘grazer-type’ morphologies forming the end-members.

This hypothesis is based on the inference that classifying what are intrinsically

morphologically diverse organisms into discrete clusters is problematic and somewhat

counter-intuitive, if purely for the purposes of having an antecedent framework on to

which new hypotheses of functional morphology can be built.

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3.0 Materials and Methods

Geometric morphometrics is a procedure involving the multivariate statistical analysis of

two- or three-dimensional Cartesian co-ordinate data, typically involving discrete spatially-

defined landmarks (i.e. topographically homologous loci on a structure; see Mitteroecker

and Gunz (2009) for a review of techniques). Recognition that morphology is essentially the

physical manifestation of geometry is vital as a theoretical basis for biological

morphometrics. Zoological and palaeontological studies are using these techniques

increasingly due to their ability to analyse form in many different systematic contexts (e.g.,

functional morphology, sexual dimorphism, ontogenic development, allometry, and

phylogenetics) within a statistically coherent framework (see Adams et al., 2004). For more

specific examples of the recent application of geometric morphometrics in the field of

vertebrate palaeontology, see Hadley et al. (2009), Goswami et al. (2010), Jones and

Goswami (2010) and Barden and Maidment (2011).

The ruminant data set used in this investigation consisted of 121 extant species

representing 6 families and 13 sub-families. The majority of specimens are bovids and

cervids (115 out of 121), as these are the most taxonomically diverse groups. The

ornithopod data set consisted of 66 specimens comprising 34 species, ranging in age from

the Lower Jurassic to the latest Cretaceous. These were sub-divided into families; however,

the status of Heterodontosauridae and Hypsilophodontidae is equivocally unresolved

presently (see Butler et al., 2008). Taxa in these clades probably represent grades (i.e.,

basal ornithischians, and basal ornithopods respectively, both with a small, gracile body

form). The groupings into which these data are sub-divided are based on a range of

sources. For the taxonomic groupings, Butler et al. (2008), Boyd et al. (2009), and Prieto-

Márquez (2010) were used for the ornithopod data set, and Wilson and Cole (2000) for the

ruminants. Ruminant ecology was also based on a number of sources, the individual criteria

and references for which are provided in Appendix 1.

The shape groupings for both data sets were delineated arbitrarily. Initially, pointed or

blunt profiles were decided upon, simply based on whether a specimen was more blunt, or

more pointed. Exemplars are presented in Fig. 2, showing the typical pointed and blunt

14

forms, as well as what constituted the arbitrary threshold between the two. Specimens

with profiles similar to the threshold shape were delimited based on how broad the

premaxillae were before culminating in the distal end (i.e., broader ones were more

generally flatter and wider at the end opposed to those with medially-sloping lateral

edges).

No intermediate feeding group character state was used due to difficulty in assigning

group-limit thresholds (see above). A second grouping was also created in an attempt to

represent the nature of lateral shape variation in the premaxillae; pointed and blunt seem

to refer purely to the distal rostrum, without incorporating variation in the curvature of the

adjoining lateral margins. A simple qualitative addition to the shape descriptors was made

where these edges are described as concave, convex, or the intermediate shape, linear, the

three of which are largely independent of the distal geometry. Breaking down the shape in

this manner is theoretically a more precise method of describing the snout, and also breaks

down the initial groupings, which may alleviate weighting issues when using large groups.

The shape of the ruminant ‘horny premaxillary pad’ is reflected in the shape of the

underlying premaxilla (Solounias et al., 1988). It is expected that intraspecific shape

differences will differentiate less than interspecific shape differences; this is only a problem

when numerous specimens of one species are used. Therefore, only a single specimen per

Figure 2 – Exemplar species representing what constitutes a typical pointed profile (A. Litocranius

walleri), blunt profile (B. Alcelaphus buselaphus), and the transitional threshold between the two

(C. Hippotragus equinus; note that this specimen was classified as blunt).

A B C

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species is utilised here for the ruminants. In this study, this is adequate, as the intention is

to account for the between-species variation.

For the ornithopod data set, choices of which specimens to include were more complex.

Where multiple specimens of the same species are used, there did not appear to be any

consistent geometric configurations in intraspecific premaxillary shape in several of the

samples (e.g., Lambeosaurus lambei). To address these issues, putative morphotypes

groups were identified, and then analysed using canonical variates analysis (see below).

Where discrete clusters of specimens were identified and successfully discriminated, the

mean shapes of each cluster were calculated and used to replace the associated specimens

in the Procrustes transformed data set. For example, for Corythosaurus casuarius,

specimens were reduced into four discrete sub-groups based on unique morphs (specimens

1, 6 and 2, 3 and 5, and 4, 7 and 8; Fig. 3). This halves the number of specimens for this

species, thereby reducing the effective weighting of the analysis towards larger groups,

while retaining the maximum possible intraspecific shape variation and unique morph

shapes. Specimens for species such as Heterodontosaurus tucki, Hypsilophodon foxii, and

Hypacrosaurus altispinus were deemed similar enough in shape to be regarded as single

morphotypes, with their mean shapes used for all subsequent analyses.

Figure 3 – Specimens 1 to 8 of Corythosaurus casuarius in Procrustes-scaled shape space. Note the

profile similarity between the specimens outlined in the text, hence the grouping as individual

morphotypes.

16

According to Pérez-Barbería and Gordon (2000), muzzle width is strongly significantly

correlated between sexes in ruminants. However, when body mass is controlled for, this

trait scales isometrically between sexes (see also Gordon and Illius, 1994). Thus, sexual

dimorphism is not a particular problem for this analysis, at least for ruminants. Also note

that this simple metric is an over-simplification of the premaxillary morphology and so

(again) cannot be used as an accurate proxy for overall snout shape. Adult specimens were

all chosen for the ruminants (i.e., a fully erupted 3rd molar), to account for any possible

ontogenetically-coupled allometric variation (e.g., Herring, 1985).

Ontogenetic stages are unknown for the ornithopod data set (with the exception of the

sub-adult Tenontosaurus specimen; Tennant, 2010), and it is unknown if the premaxilla

exhibits allometric variation in shape through development. It is also currently unknown

whether ornithopods were sexually dimorphic with respect to premaxillary shape, although

this is an unlikely feature. Speculations on identifying sexual morphs typically revolve

around the sacral count (e.g., in Hypsilophodon foxii; Galton, 1974) cranial crest

morphology, as well as in the strength and configuration of the pelvic girdle (e.g., the length

of the post-pubic rod may be dimorphic; Chapman et al., 1997). No details regarding

taphonomic deformation are known, and it is common for fossilised skulls to be variably

compressed or distorted in the mediolateral plane. This could create the illusion of a

narrower skull, a problem suspected for at least several of the specimens here (e.g.,

Agilisaurus louderbacki; R. Butler, pers. comm.).

Regarding specimen completion, crania in which at least one half of the anterior premaxilla

was complete were selected. As crania are symmetrical about the sagittal plane, if only a

single half was preserved, the landmark co-ordinates were simply be reflected about the

sagittal plane to reconstruct the entire premaxilla (in dorsal and ventral aspects).

Body mass was not considered in this investigation as the evolution of this trait probably

reflects numerous extrinsic factors such as geography and climate (Cooper and Purvis,

2010). However, previously a relationship known as the Jarman-Bell Principle (Bell, 1974;

Geist, 1974; Jarman, 1974) found that intake rate scales to body-mass0.75, with the

17

implication that larger animals feed on a lower-quality (i.e., high-fibre, folivorous) diet

(Clauss et al., 2009). Nevertheless, Shipley et al. (1994) found that this ratio varies between

‘grazing’ and ‘browsing’ classes in extant herbivores and in both cases was lower than that

predicted by the Jarman-Bell Principle, as well as in all analysed herbivores (rate scales to

body-mass0.72). Body mass is likely to influence the intake rate as a function of oral aperture

size, and general size of an organism. As the only aspect of form of interest in this study is

pure shape, size is removed via a method known as Procrustes superimposition (see below),

and is not considered further here. Furthermore, Solounias et al. (1988) cite several

examples of organisms with an order of magnitude separating their body masses, but

similar-shaped premaxillae (e.g., wildebeest (275kg) and oribi (21kg); p. 294).

Snout profile outlines were redrawn based on the initial photographs using Adobe

Illustrator CS4. The starting point for the ruminant outline was defined as where the suture

between the maxilla and premaxilla intersects the lateral margin, from a ventral aspect.

Images provided by Norman MacLeod for the majority of the ornithopod section of this

study however were not constructed in such a manner. Nonetheless, these included the

general geometry of the distal snout, so may still provide data for analysis.

Outlines were digitized using a chain of semi-landmarks collected from the images using

Media Cybernetics’ Image-Pro Plus 7.0 software, a graphical image analysis package. The

starting landmark in the chain was always on the sinistral maxilla-premaxilla junction,

ensuring that all subsequent semi-landmarks were interpolated to be topographically

homologous with respect to a significant morphological feature.

One hundred equally spaced semi-landmarks were collected along the outlines for both

data sets, as this provided a geometrically faithful representation of the profiles. Each semi-

landmark has a defined x-y position with respect to the co-ordinate system origin. As the

purpose of this investigation is to analyse pure shape variation in the peripheral margins of

the sample premaxillae, no inferences can be made about the internal geometry of the

structures since they are not covered by the semi-landmarks. Size was not intended as a

target for analysis, so scale information was not recorded. A three-dimensional approach

18

where snout depth would be analysed was also not deemed necessary, as this is not

considered to interact in any way with gape and hence oral intake.

All programs for the geometric morphometric analysis were created in Wolfram’s

Mathematica (vers. 8.0). The initial landmark data for both ornithopods and ruminants

were subjected to a two-dimensional Procrustes (GLS) transformation (vers. 3.8; Rohlf and

Slice, 1990). Procrustes superimposition forms the core of analysis of pure shape, by

removing the extraneous variation in scale, orientation and position for all specimens’ semi-

landmark constructions (see Box 2 of Klingenberg, 2010). Optimising the fit of all specimens

to each other was achieved by the rigid rotation iterating until the distance between

successive mean landmark configurations fell below 0.0001. This provided the ability for

progression of analysis in shape space as opposed to form space. The output was a series of

Procrustes-scaled shape co-ordinates for each specimen, as well as the mean shape co-

ordinates and centroid size values. The specimens at this stage were sub-divided into their

various sub-groupings for each subsequent analysis (see the Results section).

These superposed data were subject to a covariance-based principal components analysis

(PCA vers. 3.7; MacLeod, 2005), a method of eigenanalysis that preserves the Procrustes

distances among specimens (Mitteroecker and Gunz, 2009). Principal component analysis is

a rigid rotation of the initial ordination to new orthogonal principal component (PC) axes,

with scores for each axis that totally represent 100% of the maximum initial variance. For

geometric simplicity, the arbitrary threshold of 95% variance is used (i.e. using the

minimum number of PC axes that describe 95% of the total variation), as it characteristically

provides adequate explanatory power with substantially lower dimensionality (the total

dimensionality for the data set is 200). Here, four principal component axes (eigenvalues)

explained greater than 95% of the variance for both data sets, so were selected on this

basis (Table 1).

The principal component scores for both data sets were then subjected to a canonical

variates analysis (CVA, vers. 1.8; MacLeod, 2007). This multivariate technique transforms

the data to re-ordinate it against the axes which can discriminate best between group

19

centroids by finding new shape variables that maximise the inter-group variation with

respect to the intra-group variation (Campbell and Atchley, 1981; MacLeod, 2007;

Klingenberg, 2010). The purpose of this procedure is to firstly, using PCA, reduce the shape

variation into a smaller, manageable number of variables, and then use these as a basis for

discriminating between groups. A chi-squared likelihood ratio test was performed to test

group distinctiveness (i.e. group dispersion structure) of the data, with respect to the

sample that defines the discriminant space (MacLeod, 2007a). The resulting Χ2 probability is

a validation test of the between-groups covariance structure; i.e. a low probability (<0.05,

traditionally) reflects statistically significant difference in the covariance, or dispersion,

structure with respect to the defined groups. This implies that the groupings are the

products of some extrinsic factor, such as biogeography, phylogeny, functional constraints,

or ecology, as opposed having a stochastic distribution. A group distance table is also

provided, showing the distance of all objects (specimens) from the group centroids. This is a

representation of the consistency of the pre-defined groups and the accuracy in which they

are constructed (i.e. the reliability of being able to reconstruct and discriminate the groups;

MacLeod, 2007a). These distances are also summarised in the form of a ‘confusion matrix’,

a tabulation that summarises the accuracy that specimens will be correctly assigned to their

a priori allocated groups through a Mahalanobis distance analysis (MacLeod, 2007b).

The number of orthogonal canonical variates axes corresponding to the number of pre-

defined groups minus one (i.e. the minimum number of axes required to demarcate

groups), with five modelled points per axis, were retrograded through the canonical

transformations (i.e., scalings and rotations) and back-projected into the space of the raw

principal components (MacLeod, 2007b). These points represent that two extreme points,

the central point, and two medially-interpolated points between these on the CV axes. The

result is a set of non-orthogonal canonical variates (i.e. discriminant axes) oriented with

respect to the data within Procrustes-scaled PCA space. Each model axis was plotted using

the program Axis Models (Co-ordinate point and strobe plots, vers. 1.1; MacLeod, 2009) in

a representation of deformation along the CV axes in the PCA shape space. These ‘strobe

20

plots’ show a transformation sequence through the data based on hypothetical successive

models of the snout profiles in a space defined by maximum shape variation.

21

4.0 Results

4.1 Procrustes Superimposition

Procrustes transformation provides a user with a data set of superimposed co-ordinates for

analysis of pure shape. Three ordinations were produced for each data set – the mean

shape, an overlay plot for all specimens, and a grid of all Procrustes-scaled semi-landmark

constrained representations of the specimens snout profiles. The mean shape and

complete datasets are illustrated for the ruminants (figs 4a and b) and ornithopods (figs 5a

and b).

Figure 4 – The Procrustes-scaled mean premaxilla shape (A) and overlay plot (B) for all 121

ruminant specimens. Note the almost continuous variation between a ‘blunt’ and ‘pointed’ shape

in the distal tip in B.

A

A B

A B

Figure 5 – The Procrustes-scaled mean premaxilla shape (A) and overlay plot (B) for all 66

ornithopod specimens. Note the similar variations in shape to the ruminant specimens, and also

the mediolateral compression of the mean shape. The slight lateral distortion of the mean shape

may be a taphonomic artefact (i.e., post-burial deformation).

A

22

4.2 Ecological Classification

Covariance trends within these data were summarised using PCA with the resulting scores

being plotted in both two dimensional and three dimensional spaces. All two dimensional

ordinations plot PC-1 against PC-2. The three-dimensional plots additionally show PC-3. For

the ruminants, five different primary groupings were defined, resulting in five analyses

being performed. This was to see the degree to which premaxilla shape covaries with

different taxonomic and ecological groupings, as assessed by a CVA.

When ruminants are grouped according

to feeding strategy, there is no clear

pattern or structure distinguishing the

shapes between either of the feeding

categories in the space formed on the

first two PCA axes, although grazers do appear relatively confined in this PC space,

compared to the completely indistinguishable browsers, frugivores, and intermediate

feeders (Fig. 6). Inclusion of PC-3 shows that frugivores clearly occupy a subspace apart

from grazers, but are indistinguishable from adjacent browsers and intermediate-grade

species (Fig. 7).

Grazers appear to form a well-defined wedge, with substantial overlap between the

remaining categories. Intermediate forms exceed the browser shape envelope in three

directions (all but the negative PC-1 direction). Several intermediate species not only

increase the range of shape variation, but also occupy more extreme shapes than browsers.

Species classed as having ‘intermediate’ feeding strategies clearly do not occupy

‘intermediate’ positions with respect to the premaxilla shape space as represented by PC-1

and PC-2 (and PC-3). The overlap is also not distributed evenly between the two end-

member groups; both appear to be more similar to browsers. Even if intermediates are

removed, ruminants classed as either ‘browsers’ or ‘grazers’ maintain about 40% overlap in

their shape domains. However, this result may reflect the wide range of methods or

characteristics that were used to create the a priori classifications. Only five browsers (Alces

pulmatus, Rhynchotragus domorensis, R. guentheri, R. kirkii, and Madoqua phillipsi), five

PC-1 PC-2 PC-3 PC-4 Total

96.662

68.735 20.184 3.831 2.691 95.441

73.430 16.031

Data Set

4.039 3.161

% Variance Explained

Ruminants

Ornithopods

Table 1 – Calculated principal component

eigenvalues for both the ruminant and ornithopod

Procrustes-transformed data sets.

23

intermediates (Hydropodus inermis, Rangifer tarandus, Gazella gazella, Antidorcas

marsupialis, and Dorcotragus megalotis) and six grazers (Oryx leucoryx, Connochaetes

taurinus, C. gnou, Damaliscus albifrons, Kobus leche, and Beatragus hunter) can be

unequivocally resolved in Figure 6 as belonging to their assigned groups, a 14% success

rate. The fact that all 3 major groupings exhibit significant overlap in the centre of the

ordinations indicates that within each group, there are numerous individuals with their

premaxilla shape essentially identical to that of the mean shape for the combined data set.

The range and continuous nature of the overlapping region is indicative of continuous

within-group variation about this region of the grand mean. Both of these factors suggest

that group separation based on premaxillary profile is problematic. This is not to say that

group separation is not present, it simply is not being conveyed with respect to the first two

principal components (theoretically they can be separated in any combined plot of PC-a

against PC-b).

Figure 6 – Two-dimensional PCA score plot for ruminants classified according to feeding type.

The information for this plot is based on numerous sources (see Appendix 1). The amount of

variance each PC axis describes is given adjacent to the respective axis labels.

24

Figures 8 and 9 show the results of a canonical variates analysis (CVA) of the PC scores in

two and three dimensions, respectively. In Figure 8, browsers and intermediates occupy

similar canonical variate (CV) space regions with respect to the first two axes. Grazers

occupy a distinct region, apart from the other two major groups, occupying higher values

along the CV-1 axis. The overlapping nature of the groups in figures 8 and 9 implies that the

within-groups shape variation is distributed in such a manner that there is little or no

evidence for between-group shape discontinuities existing for these data. The introduction

of CV-3 into the ordinations appears to make the groupings increasingly convoluted, with

no apparent between-group discrimination (Fig. 9). The ordinations resulting from these

analyses demonstrate that for premaxilla shape there is a lack of consistency between the

groupings in terms of group-specific shape differences, when grouped according to a

secondary criterion that defines their feeding strategy (Appendix 1). Figure 9 shows that

discontinuities cannot be found within the groups in CVA space, as the variation shown

between groups is distributed in too broad a manner. This leads to rejection of the

hypothesis that ruminants develop different snout shapes according to their feeding

strategies, and acceptance of the null hypothesis that there is no significant difference

Figure 7 – Three-dimensional PCA score plot for ruminants classified according to feeding type.

Note that PCA is not designed to pull apart groups, but to re-orientate data along axes that

describe the highest shape variation. Legend as Figure 6.

25

between feeding strategy groups in terms of premaxilla shape, when the profile is used as a

proxy for gross snout morphology.

Figure 8 – Two-dimensional canonical variates score plot for ruminants classified corresponding to

feeding type. The quantity of variance each canonical variate describes is shown adjacent to the

respective axes.

Figure 9 – Three-dimensional CVA score plot. There is little in the way of group discrimination, based

on a priori classification according to feeding strategy. Considering CVA is specifically designed to re-

orientate the data along axes of maximum group discrimination, the intricate relationships here

indicate that the classification system used here is inadequate. Legend as Figure 8.

26

The slight structure grazers exhibit in Figure 8 is lost as they are pulled into the

amalgamation of intermediates and browsers. Moving on, the next phase was plotting the

CVA results for this grouping set. In Figure 10, the CV axes are marked by black points

representing the locations of along axis shape models in the CVA ordination space. Three

axes were modelled for the ecology-based analysis (the third not shown in Figure 10). But

when all discriminant axes are back-projected into their corresponding PC-space

orientations, the relative orientations of the CVA axes becomes apparent (Fig. 11). Figure

12 shows the results of a likelihood ratio test of the separation of group means relative to

their within-group dispersions (see Satorra and Saris, 1985). The resulting ratio here is 0.0,

indicating that the likelihood of these groups occupying their positions in the overall CVA

space as a result of the effect of random sampling of a single, underlying population is 0.0.

Accordingly, the alternative hypothesis - that these data were drawn from different shape

populations with different characteristics - is accepted.

Figure 10 – Orientation of CV-model axis 1 (horizontal) and CV-model axis 2 (vertical) in two-

dimensional CV-shape space. Each individual modelled point (in black) represents a specific

point on its CV axis. Legend as Figure 8.

27

One of the more appealing aspects of geometric morphometrics is its ability to support

visualisation of the changes that are occurring within the ordinations; in this context, a

‘strobe plot’ (Lohmann and Schweitzer, 1990; MacLeod, 2009) of the CV-models in PC space

shows the progressive deformation from one end of the shape spectrum within the

maximum shape envelope described by the ruminant specimens’ premaxillae (Fig. 13). The

shape variation described by these three axes can evidently not be described as simply as a

continuum from ‘blunt’ to ‘pointed’. The first CVA axis shows progressive deformation of

the premaxilla, with a distal compression into a slight bowing, concurrent with

anterolaterally-directed expansion into a laterally-deflecting curvature. The second CVA

axis describes similar variation, but on a smaller scale, and with a slight lateral deflection of

the proximal region adjacent to the maxilla-premaxilla suture. The third axis describes the

least variance, but describes an alteration from a fairly broad-tipped shape, with

posterolaterally directed margins to a distally expanded and increasingly laterally

compressed shape. The result is that snout shape, with a two-dimensional profile in ventral

aspect as a proxy, is not sufficient to differentiate between and classify ruminants into

grazers, browsers and intermediates. The implication, is that snout shape is unrelated to

other putative functional traits that distinguish between the feeding types (e.g., the

Figure 11 – Back-projection of the CV-model axes into the respective PC shape space. Note that

the length of the model axes is inconsistent here, due to their respective orientations and

restriction to two-dimensional PCA space. Legend and axes as Figure 6.

28

hypsodonty index, percent of grass consumed; see Appendix 1; note that where conflict

arose, priority was given to the most recent classification), or that there is some subsidiary

function that it serves. It could equally be that ruminants are so uniquely diverse, and have

adapted to maximise resource exploitation in their respective ecosystems, that they exhibit

widespread morphological convergence on the various snout shapes, forming a continuum

of shape variation with each particular species occupying a defined point relating to a

specific suite of ecomorphological characteristics.

Figure 13 – Strobe plot of the CV-model axes in PCA space. The rows correspond to the respective

axes (e.g. row 1 represents model axis 1), and the columns are each point on that axis. The right-

hand column is an overlay plot, showing the progressive shape deformation between end-points

on the axis. The more external models are increasingly further from any specific specimens (Fig.

11), and represent a hypothetical point in shape space encapsulated by the shape envelope for all

specimens.

Figure 12 – Χ2 probability density function plot. The result describes a statistically significant

likelihood of non-random data (i.e., that some alternative signal is controlling the distribution

of the data).

29

4.3 Taxonomic Classification

Figures 14 and 15 are ordinations of the ruminant specimens at the taxonomic level of

Family (see Appendix 1). One would typically expect, that based on common ancestry,

organisms within the same family would exhibit more similarity than those between

different families (see Figure 12.3 in Jones and Goswami, 2010). In both plots, it is apparent

that both major families (Bovidae and Cervidae) show significant overlap between their

premaxillary shapes. Shape variation in both groups is spread continuously along the major

axis of shape variation, PC-1. Unfortunately, three of the studied families are only

represented by a single specimen (Giraffidae, Antilocapridae, and Moschidae), so it is

impossible to assess intra-family shape variations for them. Tragulids occupy a small niche

of shape space, nested within the amalgamation of cervids and bovids, with PC-2 and PC-3

somewhat distinguishing them from the other specimens (Fig. 15).

When studying functional morphology, a portion of the covariance between organisms may

be the result of phylogeny, were the patterns being produced are governed by the fact that

closely related organisms tend to be more similar than further related ones. Ideally, shape

variation is structured in a manner that is adaptational and reflects functional groupings

(e.g., based on feeding strategy). If the former was prevalent, one would expect to see

patterns in shape variation reflected at various levels in higher taxonomic groupings. In this

case, this type of patterning would that would be reflected as a well-structured

differentiation between Cervidae, Bovidae, and the other families, a pattern that is not

observed in the principal component ordinations at either the family level (Figs. 14 and 15)

or sub-family level (figs. 16 and 17). Instead of there being evidence for a confounding

phylogenetic signal, what is apparent is that there is widespread convergence, and possibly

parallelism, between all ruminants into a continuum of shape variation, with neither

forming discrete clusters based on premaxillary shape. This implies that an adaptational or

functional signal is prevalent with regards to this trait.

30

Figure 14 - Two-dimensional PCA score plot for ruminants classified corresponding to their

family. Note that the PC eigenvalues are identical to the other PCA plots. Even individual genera

cannot be constrained into morphospace groupings (e.g., Gazella).

Figure 15 - Three-dimensional PCA score plot for ruminants classified corresponding to their

family. Legend as Figure 14.

31

Figure 16 – Two-dimensional PCA score plot for ruminants grouped according to their sub-

family (or family for Tragulidae, Moschidae, and Giraffidae, as they only contain one specimen).

Figure 17 – Three-dimensional PCA score plot for ruminants grouped according to sub-family.

Legend as in Figure 16. With little or no discernible clustering of similarly classed organisms in

shape space, it can be inferred that phylogenetic relationships are acting only in a minor way, if

at all, to occlude true adaptational patterns. Members of Antilopinae however are clustering

towards the higher end of PC-1, which may be due to the high specimen to genus ratio (i.e., few

genera, many species).

32

Figure 19 – Three-dimensional CVA score plot for ruminants classified according to their family.

Bovids and cervids maintain significant overlap with respect to all three axes, indicating that the

shape variations exhibited are more homoplastic in nature than phylogenetic (i.e., related to

ecology or functional constraints). Legend as in Figure 18.

Figure 18 – Two-dimensional CVA score plot for ruminants grouped classified according to their family.

33

The absence of any controlling phylogenetic signal is observed when the above data are

subject to a CVA. If premaxilla shape was being controlled by phylogeny, then the

specimens would be drawn into their taxonomic clusters reflecting similarity based on

common ancestry. Figure 17 shows the overlap between Bovidae and Cervidae more clearly

– they are indistinguishable at this level based on premaxilla shape, indicating that there is

an extrinsic factor excluding phylogeny that is controlling their distibution. This is also seen

in the three-dimensional ordination (Fig. 18). Tragulids occupy a small domain in the overall

canonical variate space, suggesting that the three species of the genus Tragulus have

adapted to occupy a similar ecological role. These three browsers also occupy similar space

when grouped according to feeding strategy. This pattern of subspace occupation may be

associated with the fact that these species are georaphically constrained to southern and

south-east Asia, are an ancient lineage forming the sister group to all other extant

ruminants, and are the smallest extant ruminants known (Meijaard and Groves, 2004).

Their ecological role is significant for this study, as similarly to key basal ornithischians, they

have premaxillary ‘tusks’, analogous to species such as Heterodontosaurus tucki. This does

however indicate that, with respect to tragulids, a minor aspect of phylogenetic patterning

exists within the ordinations.

Figure 20 – Two-dimensional CVA score plot for ruminants classified according to their sub-family.

Whilst there does appear to be a degree of clustering for several groups (e.g., Reduncinae), the

amount of overlap between groups suggests that the phylogenetic signal is being over-ruled by a

subsidiary factor.

34

When classified according to sub-family (figs. 19 and 20), ruminants exhibit similar patterns

to when they are classified according to family, but with slightly tighter clustering for

several groups (e.g., Hippotraginae). This is to be expected, as when taxonomic resolution

increases at lower levels, the organisms by default will be more closely related than at

higher taxonomic levels. There is, however, the problem that comparatively, the

hierarchical taxonomic levels used here may not be comparable in terms of definition (i.e.,

currently there is no strict definition describing what constitutes the family or sub-family

boundaries). It follows that the various clades represented within Ruminantia may not be

directly comparable, due to their differences in phylogenetic history, which is not reflected

in their taxonomy.

Figure 21 – Three-dimensional CVA score plot for ruminants classified according to their sub-

family. Legend as Figure 20.

35

4.4 Shape Classification

This aspect of the analysis required a priori classification of all specimens based on the

general shape of their premaxillae. The aim was to see initially if the simple classification

scheme of ‘pointed’ and ‘blunt’ was, firstly, adequate to encapsulate the entire geometry of

the ruminant snout (excluding size), and secondly to see if visual assignment of species to

these groups could be supported in a statistical framework.

When classified according to whether the snouts were blunt or pointed, little resolution

was acquired through PCA (Fig. 22). The third PC axis appears to increase the complexity of

relationships between the two groups (Fig. 23). The implication is that this terminology is

largely inadequate to describe the total range of shape variation that ruminant snouts

exhibit. Many ruminants classed as either pointed or blunt occupy the PCA morphospace of

the opposite group. This may be due to either incorrect a priori classification, or that the

shape the PC axes are describing goes beyond the curvature of the distal snout tip. When

the data are subject to a CVA, there is little in the way of additional resolution. This is

somewhat surprising, as CVA is designed to pull pre-defined groups apart by maximising the

distance between the group centroids relative to the group dispersions. The reorientation

of the data into the CV space maintains a similar level of inter-group distinction to the

Figure 22 – Two-dimensional PCA score plot for ruminants based on the a priori classification of

their general snout shape (the primary shape descriptor).

36

ordination in PC space (Fig. 24). A possible reason for this is that, again, the level of

classification is insufficient to encapsulate the complex morphological diversity of ruminant

premaxillae. As mentioned before, ‘pointed’ and ‘blunt’ profiles only form the end-member

classifications, supposedly representing the extremes of ‘browsing-’ and ‘grazing-type’

ruminants respectively, with intermediates between forming a shape continuum between

the two. This intermediate phase has been neglected here, to reduce the impact of an

additional arbitrary threshold – without a secondary criterion directly linked to snout shape

that can also discriminate between feeding strategies, any arbitrary threshold created here

cannot be empirically validated. The lack of group-resolution in the CVA space defined by

the first two CV axes indicates that the level of intra-group variation is overpowering the

inter-group variation to an extent that their distribution clouds are unable to be recovered

as completely discrete.

Figure 23 - Three-dimensional PCA score plot for ruminants based on the a priori classification of

their general snout shape. Legend as Figure 22.

37

The above ordinations demonstrate the deficiency in descriptive power that the terms

‘pointed’ and ‘blunt’ contain when the snout profiles are delimited in this fashion, albeit in

a qualitative and somewhat subjective manner. Increasing the quality of the descriptive

terms in the secondary shape descriptor increases their explanatory power as well as

increasing their precision. Due to the relative ease in identifying whether a curve is straight,

convex, or concave is straightforward, this should not increase the uncertainty for the

qualitative delimitations. These additional terms were combined with the primary profile

shape descriptors to increase the number of groupings to six; this should in theory reduce

the intra-group variation and lead to increased clarity in the discrimination analysis by

increasing the inter-group variation. A 2D ordination in PCA space is shown for this new

grouping in Figure 25. The first two PC axes here describe almost 90% of the variance. The

plot shows the relative positions of the six groups in the space defined by the first two

principal components, and the complexity of the overlaps is rather apparent. Inclusion of

the third principal component further increases the convoluted distributions, although it

does seem to restrict the pointed-class specimens to the positive end of PC-2 (Fig. 26). No

single group is entirely captured within the space envelope of another, providing slight

resolution.

Figure 24 - Two-dimensional CVA score plot for ruminants based on the a priori classification of their

general snout shape. The shape envelopes in this space maintain a similar degree of overlap to the

associated PCA ordination.

38

Figure 25 – Two-dimensional PCA score plot for ruminants classified according to the secondary

shape description.

Figure 26 – Three-dimensional PCA score plot for ruminants classified according to the secondary

shape description. Note the broad distribution of all groups with respect to PC-1, except for the

‘blunt-convex’ group, which appears to be restricted to negative values.

39

When subjected to a CVA, the new groupings are ordinated in space with high explanatory

power (97% covariance in the first two CV axes). As in the PCA ordination, ruminants with a

‘blunt-concave’ (in the format ‘distal tip-lateral margin) profile occupy a large space

domain, with most of the specimens well discriminated from the other groups (although

still with a high degree of overlap for many others). The ‘blunt-linear’ and ‘blunt-convex’

groups occupy a highly similar position in the space, and are clearly more similar to each

other than to the third ‘blunt’ grouping. All three are fairly well constrained with respect to

CV-1, mostly with scores greater than 0.05 on this axis. With the exception of several

specimens grouped as ‘pointed-convex’, the ‘pointed’ domain appears confined to scores

less than 0.05 on CV-1. The ‘pointed-linear’ and ‘pointed-concave’ groups occupy similar CV

space, and are both largely confined within the ‘pointed-convex’ space. All ‘blunt’ and

‘pointed’ groups maintain a degree of overlap with their opposites. This ordination provides

further evidence that, despite an increase in resolution and descriptive power, snout shape

cannot be easily discriminated into discrete groups, and instead forms a continuum, likely

with ‘pointed-convex’ and ‘blunt-concave’ profiles occupying end-members of the shape

spectrum. All other specimens can be placed within this continuum, but restricting them to

discrete groups is not only unsupported, but acts to reduce the distinct morphological

complexity exhibited in the ruminant premaxillae.

Figure 27 – Two-dimensional CVA score plot for ruminants classified according to the secondary

shape description.

40

Following the method outlined above, strobe plots were constructed for both profile shape

categories. For the first category, only a single discriminant axis was possible to model due

to the presence of only two sub-groups (Fig. 28).

The resemblance of Figure 28 to the first modelled axis when the ruminants are classified

according to their feeding strategy is intriguing (Fig. 13). The axis is reversed, a

phenomenon that can be ascribed to the arbitrary direction of the principal component

axes (MacLeod, 2005). The differences between the two plots are subtle: in Figure 13, the

anterolateral expansion tapers more gradually towards the maxilla-premaxilla suture,

whereas in Figure 28, the expansion rapidly pinches posteriorly, developing into a

secondary proximal lateral expansion. The expansion of the distal tip is also slightly less

Figure 28 – Single strobe plot of the CV model axis in its respective PCA space.

Figure 29 – Strobe plot for the 5 modelled CV axes in PCA space when the shape descriptor

complexity is increased.

41

pronounced in Figure 28. One implication of this similarity is that the transformation

sequence seen here may be enough to describe variations in feeding strategy. One end of

the spectrum would be occupied by specimens with a proximally compressed, distally

expanded, and relatively blunt snout, the other by a proximally expanded, distally rounded

and compressed snout. This is slightly more complex than simply ‘blunt’ and ‘pointed’, and

describes the shape variation along the length of the premaxillary profile. However, this

does not mean that either of these shapes adequately describes or defines the archetypal

snout profile for either browsing or grazing ruminants; this dichotomy remains unresolved

in terms of snout shape. The modelled strobe plot for the second shape category exhibits

much the same sequence of deformation for the first axis as the initial category, although

the variation is less pronounced (Fig. 29).

The second modelled axis exhibits strong deformation between an initially

anteroposteriorly compressed and laterally broad profile, into a progressively lengthened

and mediolaterally compressed profile (Fig. 29). The third axis retains uniformity around the

distal half, with deformation occurring proximally with increasing lateral expansion towards

the maxilla-premaxilla suture. The fourth axis is unique among all modelled axes, in that it

clearly lacks the deformational symmetry of the others, and is distinctly skewed both in the

mediolateral and anteroposterior dimensions. The causes for this are possibly due to error

in the profile reconstructions, but perhaps attributable to the fact that these represent

hypothetical models, not genuine specimens, and perhaps represent an unrealistic and

extreme deformity of the profile

shape. The fifth axis displayed no

visible deformation patterns.

Table 2 shows the results of a

likelihood ratio test performed on the

data subsequent to their respective

canonical variates analyses. The

statistical significance of the ecology-based analysis has been mentioned previously.

Statistically significant results were also recovered when data were grouped based on their

Table 2 – Results of the chi-squared likelihood test for

all ruminant groups. Note how all analyses are

statistically significant in CVA space, except for when

the specimens are grouped by Family.

GroupingObserved

Φ- value

Degrees of

FreedomProbability (%)

Family 30.77 15 0.942

Subfamily 134.8 45 6.764E-09

Shape I 43.29 3 2.132E-07

Shape II 91.15 20 4.054E-10

Ecology 55.84 12 0

42

sub-family and both shape categories. Somewhat perturbingly, almost the exact opposite

was found for the data when grouped by family. This likelihood value may be the product of

the way the data was grouped, as the classifications were dominated by the Families

Bovidae and Cervidae. If so, then it is somewhat paradoxical why a similar result was not

recovered for the first shape category (i.e., ‘blunt’ or ‘pointed’ profiles).

When ruminants are classified ecologically as browsers, grazers, intermediates, or

frugivores based on a range of secondary criteria, they cannot be discriminated based on

the shape of their premaxillary profile. Instead, snout shape appears to be homoplastic in

nature, with a broad range of geometries present in each of the feeding style groups.

Furthermore, previously used descriptive terms such as ‘pointed’ and ‘blunt’ are not only

inadequate to partake in defining these groups, they also like the descriptive power to

define the shape variation that ruminant snouts so visibly demonstrate. Refinement of

these terms to describe a more complex geometry leads to increased resolution of more

precisely-defined groups, but still a lack of demarcation into spatially discrete clusters.

These results are confirmed as statistically significant using a chi-squared likelihood

assessment, and are also found not to be an artefact of phylogenetic affinity, although this

inference is somewhat dubious (i.e., statistically non-significant data when grouped by

Family, and qualitative assessment of phylogenetic relationships in shape space).

Given the above inconsistencies with previous assumptions, to what extent can the

patterns found here be extrapolated back to ornithopods, given that little can be explicitly

defined in terms of classifying feeding strategy in terms of snout morphology? It is evident

that individual ruminants occupy specific positions in a continuum of shape variation,

irrespective of phylogenetic affinity and putative pre-defined feeding strategy. Although

demarcating specific thresholds for groups such as ‘browsers’ and ‘grazers’ is problematic,

given their overlapping nature with respect to a premaxilla-based profile shape analysis, it

is apparent that specific shapes represent the end-members of the continuum.

43

To see exactly how ornithopods are related to ruminants in terms of premaxillary shape,

the PCA scores for the reduced ornithopod data set were projected into the PC space

created by the first two principal components for when ruminants are classified according

to feeding strategy (Fig. 30). There is both significant overlap with for many specimens, and

definition of a particular ornithopodan morphospace.

Closer inspection shows that this pattern has a strong structure relating to the phylogenetic

positioning of the ornithopods (Fig. 31). Although every morphospace defined by each

particular class of ruminants exhibits strong overlap with the others, it is noteworthy that

the only ornithopods that similarly occupy this space are the more primitive species (e.g.,

heterodontosaurs, hypsilophodonts, iguanodonts). Hadrosaurs occupy their own defined

space away from ruminants, along with several iguanodonts and, surprisingly,

Heterodontosaurus tucki. This strongly challenges the viewpoint that ungulates and

hadrosaurs are ecologically analogous (e.g., Carrano et al., 1999), in spite of the fact that

snout shape is a poor reflection of feeding strategy. Regarding the species that do fall into

ruminant space, there is a slight structure evident in their distribution. Only two can be

unequivocally assigned putative feeding strategies; Zalmoxes robustus is placed within

Figure 30 – Projection of the ornithopod PCA scores into the space defined by the first two PC

axes for the ruminants, with ruminants shown classified according to their feeding strategy (see

Figure 6).

44

‘grazer’-defined space, and Zephyrosaurus schaffi in ‘intermediate’-defined space.

Specimens placed within space where all three groups overlap are all of hypsilophodont-

grade (e.g., Oryctodromeus cubicularis, Changchunsaurus parvus), and those placed within

either ‘browser’ or ‘intermediate’ groups include most of the iguanodont-grade specimens

(including also Camptosaurus dispar and Dryosaurus lettowvorbecki), the remaining

hypsilophodonts, and the heterodontosaur-grade Agilisaurus louderbacki. Tenontosaurus

dossi, Heterodontosaurus tucki, and Telmatosaurus transsylvanicus (the most basally-placed

hadrosaur analysed here) are all placed close to the ‘grazer’-defined space, but within the

predominantly hadrosaur-defined ornithopod domain. This may open up pathways for

further investigations into what can be inferred about the digestive or ingestive physiology

of these organisms, but given the ambiguity surrounding the browser-grazer dichotomy,

any extrapolations made will only be tentative at best.

BrowserCamptosauridaeDryosauridaeFrugivoreGrazerHadrosauridaeHeterodontosauridaeHypsilophodontidaeIguanodontidaeIntermediateRhabdodontidae

Figure 31 - Projection of the ornithopod PCA scores into the space defined by the first two PC

axes for the ruminants, with ruminants shown classified according to their feeding strategy.

Ornithopods are shown categorised according to their Family. PC axes as Figure 6.

45

When the ornithopod data set is exclusively ordinated, the hierarchical pattern between

taxonomic groupings becomes apparent (Fig. 32).

The structure in Figure 32 shows a transition along PC-2 from heterodontosaur-grade

species, sequentially through hypsilophodont-grade and iguanodont-grade species, and

finally hadrosaurs which occupy the broadest region of shape space. If iguanodontids are

removed, the spatial structure each group occupies is very distinct. The iguanodontians

located in the hypsilophodont domain are Fukuisaurus tetoriensis, Theiophytalia kerri, and

the second morph of Tenontosaurus tillettorum. The former is considered a relatively small

species, which may be cause for its position here. Theiophytalia, in a recent analysis by

McDonald (2011) was found to be a basal member of the clade Styracosterna, placing it as a

close relative to Camptosaurus; indeed, this species was long considered a camptosaur until

reassignment by Brill and Carpenter (2007). The current taxonomic status of Tenontosaurus

tillettorum is equivocal, with authors unable to decide if it should be placed within

Iguanodontia, outside the group with the other basal ornithopods in a hypsilophodont-

grade melange, or even assigned its own Family with the congeneric T. dossi. Given this

information, it is possible to infer that snout shape here forms a continuum, analogous to

ruminants, and strongly reflects a phylogenetic signal. Dryosaurs and camptosaurs appear

Figure 32 – Two-dimensional PC score plot for ornithopods when classified according to their

family level.

46

to occupy the middle ground between hypsilophodonts and iguanodonts, as expected.

However, their spaces are poorly constrained due to lack of specimens. The substantial

overlap between iguanodontids and hadrosaurs is postulated here to be the result of a

moderate component of ontogenetic shape variation, with physically younger hadrosaurs

morphologically representing the phylogenetically more basal iguanodontians. This pattern

of phylogenetically-related shape change is also evident when these data are subject to a

canonical variates analysis. The groupings are discriminated marginally more, with the

exception of Zephyrosaurus schaffi, which again occupies a place between hadrosaurs and

iguanodonts (Fig. 33).

This apparent transitional structure between progressively more advanced groups may be

an artefact of the ages of the species. Although ornithopods exhibit a defined temporal

phylogenetic hierarchy, this may enhance or distort the signals reflected in snout shape

observed here. Accordingly, the specimens were categorised in broad groups according to

their chronostratigraphic geological age. If similar patterns are observed between

phylogenetic and temporal trends, then this would provide strong support for previous

Figure 33 – Two-dimensional canonical variates score plot for ornithopods when classified

according to their family. The transition between groups is constrained to CV-1.

47

assertions that, not only did masticatory complexity in ornithopods increase through time,

but also that it occurred in a step-wise manner with a strong phylogenetic structuring.

Figure 34 shows a discriminant plot for the ornithopods when they are coarsely classified

into chronostratigraphic groups. What is immediately apparent is the under-representation

of species from the Lower and Middle Jurassic. Upper Jurassic species (i.e., Camptosaurus,

Dryosaurus) are moderately constrained to the space defined by Lower Cretaceous

specimens (dominantly iguanodonts and hypsilophodonts). Despite the poor temporal

sampling, there is an apparent pattern of increasing morphospace occupation from the

Upper Jurassic to the Upper Cretaceous, although this may purely be an artefact of sample

size. If this is a genuine pattern however, it implies that at some point between the Lower

and Upper Cretaceous, there was a remarkable increase in snout shape variation. The

distal-most species creating this broad space include the lambeosaurine hadrosaurs,

Oryctodromeus cubicularis, and Zalmoxes robustus, indicating that this morphological

radiation is not purely confined phylogenetically. The possibility that an external factor is

driving, or being driven by, the increased snout shape variation can, therefore, not be

excluded.

Figure 34 – Two-dimensional canonical variates score plot for ornithopods broadly classified

according to their chronostratigraphic ages. Unfortunately, Jurassic species are poorly represented

in this aspect.

48

To observe the shape change occurring along the CV axes, the procedure applied to the

ruminant data set was followed, with five modelled points per CV axis (for four axes) being

back-projected into the PC space defined by the first two principal components, which

together explained 88% of the total variance (Fig. 35).

The pattern of morphological

variation is even more apparent in

Figure 35. Each subsequently older

group is entirely constrained within

the space occupied by the younger

group (from the Upper Jurassic to

Upper Cretaceous). This is almost

certainly representative of an

increase in morphological diversity as opposed to a sampling artefact, especially regarding

the Lower to Upper Cretaceous transition. Both PC-1 and PC-2 explain between-group

variation. One problem with this data is that it is not deemed statistically significant using

Figure 35 – Two-dimensional PCA score plot for ornithopods classified according to their

chronostratigraphic age. Note the progressive increase in morphospace occupation as seen in

Figure 34. Back-projected CV axis models are represented by the black points.

GroupingObserved

Φ- value

Degrees of

FreedomProbability (%)

Family 61.82 24 0.004

Age 35.05 16 0.391

Shape I 21.95 4 0.02

Shape II 49.6 20 0.025

Table 3 – Results of the Χ2 likelihood test for the four

groups in the context of the sub-groups in CVA space.

The results imply that all distributions are statistically

significant, except for when ornithopods are grouped

according to their family.

49

the traditional threshold of significance when the chi-squared likelihood test is applied.

These results are summarised in Table 3, along with the results for when this test is applied

to the other three canonical variates analyses conducted on the ornithopod data set. The

reason for this low probability in the age-defined groups is possibly attributed to that fact

that two out of the five groups only contain one member. Nonetheless, the temporal

pattern observed in Figure 35 is still clear, even if not recovered as statistically significant.

The strobe plots along the modelled CV axes show some rather peculiar results (Fig. 36).

The first modelled axis shows an almost direct vertical reflection of a distorted variation of

the mean shape, with the two end points clearly skewed distally in the lateral aspect. This

lack of symmetry seems to imply that the axis of greatest discrimination describes

taphonomic deformation in PC-defined space.

Figure 36 – Strobe plot representing the four modelled CV axes in PC-defined space. Note the lack

of symmetry in the transformations along CV-1 (and marginally CV-4), but the strong symmetry

exhibited by CV-2 and CV-3.

50

The second and third canonical variates axes describe a general lateral broadening of the

snout, proximally and distally respectively, with the respective distal and proximal regions

remaining relatively unchanged. This is also observed for CV-4, with the whole snout

broadening but with accompanying distal compression. What this illustrates is that through

time, there was a transition between a markedly ‘pointed’ snout shape to a broader, more

‘blunt’ shape, the style of transition previously posited for ruminants, but not supported in

this study. However, for CV-2, this transformation sequence actually is the reverse to both

CV-3 and CV-4, with the proximally broadened forms belonging to the Lower Jurassic

Heterodontosaurus tucki mean shape, and those with a distal mediolateral compression

being typical of hadrosaurs. The third CV axis models the transition between the Lower

Cretaceous iguanodontians and Upper Cretaceous hadrosaurs with distally-flattened

snouts, such as Gryposaurus latidens. The fourth CV axis models a transect along hadrosaur-

dominated shape space, with a variety of conspecific morphs being represented.

To observe this shape variation without the interaction of Family level groupings, the same

shape classifications used for ruminants were applied to the ornithopod data set. When

initially classified as either ‘blunt’ or ‘pointed’, a remarkably stronger pattern of variation is

found than that for the ruminant data set. A slight overlap is observed when subject to a

principal components analysis in the space defined by PC-1 and PC-2 (Fig. 37), but with the

inclusion of PC-3 in the ordination, the distinction between the two groups becomes

strikingly clear (Fig. 38). Ornithopods with a ‘blunt’ snout profile are confined to higher

values on the PC-2 axis, and occupy a broad range with respect to PC-1. Those with a

‘pointed’ profile are tightly confined in both axes to a smaller morphospace, with PC-2

differentiating moderately well between the two groups. The ornithopods occupying the

overlapping zone, classified as ‘pointed’ are not constrained to any particular taxonomic

group, whereas those classified as ‘blunt’ and occupy the overlapping zone are

iguanodontians, Dryosaurus lettowvorbecki, and the basal hadrosaur Telmatosaurus

transsylvanicus. The only hadrosaurs classified as ‘pointed’ include the mean shape for

Hypacrosaurus altispinus and the second morphotype of Prosaurolophus maximus,

51

suggesting that that this shape is uncommon for hadrosaurs, supporting the assertions

made above regarding taxonomic distinctions between hadrosaurs and the other groups.

Figure 37 – Two-dimensional PCA score plot for ornithopods classified according to the shape of

their snout.

Figure 38 – Three-dimensional PCA score plot for ornithopods classified according to their primary

snout shape. Note the almost complete distinction between the groups, contrary to the results

obtained for ruminants.

52

Somewhat counter-intuitively, this distinction is confounded when these data are subject

are subject to a CVA (Fig. 39). This is plausibly due to the fact there is a single discriminant

axis trying to differentiate between two morphologically complex groups, and the within-

groups variation is exceeding the between-groups variation to a such degree that the group

centroids are unable to be pulled apart further in CVA space. The majority of this overlap is

in fact created by the placement of the mean shape of Hypacrosaurus altispinus, which is

placed within a strong cluster of ‘blunt’-profiled hadrosaurs. Both of the specimens used to

generate the mean shape clearly exhibit a ‘pointed’ profile, which suggests that, as with the

ruminants, this classification system, despite achieving significantly higher resolution, is

partially inadequate to capture the full geometry of morphological variation in the

ornithopod snout profile.

For ruminants, the profile shape classification was moderately enhanced when the lateral

geometry was incorporated into the shape descriptors. Accordingly, the ornithopods were

subject to categorisation according to these more complex descriptions. In a plot of PC-1

against PC-2, what is instantly apparent is an increased complexity in the relationships

between the groups.

Figure 39 – Two-dimensional CVA score plot for ornithopods classified according to their primary

snout shape. Note the increased number of specimens classified as ‘blunt’ in the overlapping zone

between the two groups.

53

Those classed as either ‘pointed-linear’ or ‘pointed-concave’ are well constrained, occurring

towards the lower end of PC-2. However, those classified as ‘pointed-convex’ extend

beyond this range into a space dominated by the ‘blunt’ sub-groupings. This is possibly

attributable to the observation that, if the lateral geometry is convex-outwards, it will

generally lead to a broadening of the snout, which will give it the illusion of seeming more

blunt. This could imply that, more so than the distal shape, it is the geometry of the lateral

margins of the snout that controls the distribution of the specimens here in shape space, by

secondarily inflicting control upon the distal snout geometry. It also suggests that PC-2 is

describing shape variation acting upon the lateral margins of ornithopod snouts. When

subject to a CVA, there is little in the way of increased between-group discrimination (Fig.

41). This is possibly accountable again to high within-group variation inhibiting the ability of

the canonical variates axes to successfully discriminate completely between the group

centroids.

Figure 40 – Two-dimensional PCA score plot for ornithopods when classified according to a

secondary shape descriptor incorporating the lateral snout geometry.

Figure 40 – Two-dimensional PCA score plot for ornithopods when classified according to a

secondary shape descriptor. Note how all the specimens that create the overlap in Figure 37 are

classed here as ‘pointed-convex’.

54

The group dispersion pattern shown in Figure 41 is interesting, as it shows a tendency for

ornithopods with a ‘blunt’ prefix to group closer together, and those with a ‘pointed’ prefix

to group closer, still with moderate overlap between these two supra-groupings, and also

within the secondary groups. This suggests that it is the geometry of the distal portion of

the snout acting primarily to distinguish groups, and that the lateral geometry acts

secondarily to pull these groups apart, but still retains marginal overlap between all groups.

When the CV model axes for both of the shape groupings are back-projected into PCA

space, they both display similar patterns of shape variation along the first axis. For the first

shape-defined groups, the modelled CV axis defines a transect cutting through both the

major groupings, with the mean shape nestled firmly in the zone where the two overlap

(Fig. 42). The two extreme points of this axis are both outside the shape envelopes defined

by the data set, with respect to the first two principal components, and as such represent

only hypothetical extremes of either group. This axis represents the transformation in

shape that acts to maximise discrimination between these two groups. What is instantly

evident when these models are visualised in a strobe plot, is the insufficiency of the terms

‘blunt’ and ‘pointed’ in describing their geometry.

Figure 41 – Two-dimensional CVA plot for ornithopods when classified according to a secondary

shape descriptor. Note the size of the space occupied by those classified as ‘blunt-concave’, a

group dominated by hadrosaurs.

55

The two extreme plots represent a warping of specimens such as the fourth morphotype of

Lambeosaurus lambei along PC-1, and at the other extreme a warping of Zalmoxes robustus

the opposite direction along PC-1 (Fig. 43). Overall, the plot describes deformation from a

broad-tipped and laterally compressed shape, through the mean shape, typically

representing iguanodontians, towards a shape that is broad at the maxilla-premaxilla

junction, and tapers distally into a rounded tip, representative of specimens such as

Hypsilophodon foxii. The overlay plot here is similar to that produced for the equivalent

analysis for the ruminant data set (Fig. 28), except the deformations are more pronounced

in terms of the lateral expansion, and there is considerably less compression or extension of

the distal tip.

Figure 42 – Single modelled CV axis (black points) back-projected into the PC space defined by the

first two principal components when ornithopods are classed as either ‘blunt’ or ‘pointed’.

Legend and axes as Figure 37.

Figure 43 – Strobe plot representing the single modelled CV discriminant axis in a space defined by

PC-1 and PC-2.

56

The specimens defined by broadening of the distal tip are confined to the hadrosaurs

occupying the higher end of PC-2, and the proximally broad snout is confined to

hypsilophodonts and heterodontosaurs, with the iguanodonts and occasional members of

the other families tending to congregate around the central shape. This is a strong pattern

of variation, exhibited in conjunction with phylogenetic affinity, and also mimics the pattern

that both CV-2 and CV-3 show in Figure 36 (exclusive of the anteroposterior expansion or

compression of the distal tip of the snout), when ornithopods are classified according to

their chronostratigraphic age.

This pattern is similarly recovered when the model CV axes representing the secondary

shape categorisation are back-projected and visualised in PC space. Although given the

number of axes, it is somewhat difficult to assign them to particular species or spaces (a

problem which is also exacerbated by the overlapping nature of many of the groups), a

near-identical transformational sequence is described by CV-1 (Fig. 44).

Figure 44 – Strobe plot representing the first 4 modelled CV axes in PC space when ornithopods are

classed in a manner that more completely describes their snout profile geometry. Note that the

fifth modelled axis has been excluded here, as it showed no deformation between model points.

57

The first CV axis in Figure 44, although reversed in direction, is nearly identical to the

modelled axis shown in Figure 43, with the exception that the transformations are more

gently curving, and slightly less pronounced in the distal region. The same pattern of

deformation is evident however, with a hypsilophodont- or heterodontosaur-grade profile

occupying one end, and an advanced hadrosaur-grade profile occupying the other, relating

to ‘pointed-convex’ and ‘blunt-concave’ geometries, respectively.

The second and third CV axes represent transects through all of the group spaces, with the

exception of the ‘pointed-linear’ group. The patterns of transformation they reveal are

fairly similar, given their near-corresponding orientations in PC space. Broadly comparable

to CV-1, they represent a gradation from a laterally compressed shape into a distinct distal

laterally expanded and flattened profile, with this expansion propagating down the length

of the snout. There is also substantial distal compression accompanying this, a

transformation not picked out by CV-1. The fourth CV axis is spatially constrained in 2D PC

space, describing a near-vertical transect, with lambeosaurine hadrosaurs occupying one

end of the axis, and the second morph of Iguanodon bernissartensis occupying the other.

The variation this axis describes is deformation from a bulbous-tipped profile to one that

retains a similar distal width, but becomes moderately compressed in the mid-premaxilla

and laterally expanded proximally adjacent to the maxilla-premaxilla suture into a club-like

geometry.

The patterns indicate that initially, early ornithopods predominantly had distally-pointed

premaxilla, plausibly the plesiomorphic condition, the geometry of which was retained in

lineages such as Zalmoxes, possibly relating to its extensive isolation in the European island

archipelago (Weishampel et al., 2003). Following this, as ornithopods grew in body size and

became more morphologically complex adopting the typical iguanodont-grade bauplan, it

appears that they experimented with various snout shapes, possibly reflecting adaptation

to different diets and nutritional pathways reflecting the need for increased forage

consumption required for increasing body size. Contemporary hypsilophodonts retained

more gracile bauplans, and a more pointed snout; this may relate to increased selectivity, in

58

the manner proposed for ruminants, as they attempted to compete against the more

diverse iguanodonts.

Hadrosaurs exhibit a substantially wider and flattened distal snout compared to the other

ornithopod groups. There is currently a lack of consensus as to whether hadrosaurs were

more analogous to ground-level grazers or higher level browsers. What is apparent here is

that hadrosaurs exhibit the ‘blunt’ distal snout shape that has previously been considered

indicative of a grazing feeding strategy in ruminants, but rejected as a defining trait in the

current study. However, if the role of snout shape indeed lies in selectivity, in spite of the

fact that browsing and grazing ruminants cannot be distinguished based on snout profile

shape, it can still be proposed that hadrosaurs were non-selective feeders, with a relatively

higher intake rate.

59

5.0 Discussion

The results obtained by this study suggest a preferential method of analysis for future

investigation of functional ecology. For individual, but not necessarily independent,

morphophysiological traits, multivariate discriminant analyses with all known parameters,

while independently correcting for allometry in body mass and phylogeny, are required to

identify the traits that exhibit a deterministic influence overall on feeding strategy.

Following this, traits that operate in conjunction with each other the most strongly, once

elucidated, should be assigned functional guilds representing the ecology of distinct groups

of organisms. Pérez-Barbería et al. (2004) reached a similar conclusion in that the current

boundaries are somewhat arbitrary between feeding strategies in ruminants. A viable

approach to resolve the problem should employ a covariate or group of covariates as

continuous variables, with thresholds being based on the identification of functionally

significant and discrete clusters. However, using this methodology, the authors who have

investigated this issue so far have found no morphological discrepancies that can explain

variation in ruminant digestive efficiency based on digestive, not ingestive, morphology (see

also Janis, 1995; Clauss et al., 2003; Sponheimer et al., 2003; Clauss et al., 2008a). This

perplexing result may be, in part, due to treating species as static entities, when realistically

thresholds should be constructed on a sliding scale accounting for spatiotemporal

variations where appropriate (Owen-Smith, 1997). It also seems that general laws must be

flexible enough to account for singular exceptions (e.g., frugivores) and are insufficient to

encapsulate the full diversity of ruminant feeding habits. The real problem, however, may

stem from the fact that previous work has attempted to arbitrarily sub-divide and

categorise species that, in reality, form a continuum, with ‘browsers’ and ‘grazers’

occupying terminal points on the continuum, representing the most stationary or inflexible

feeding types. This scenario is most likely the one explained by the results of the current

investigation.

Whitlock (2011) in an analysis of diplodocoid feeding habits uses snout (i.e., premaxilla)

shape as a proxy for selectivity, and combines it with dental microwear as a proxy for

relative browse height. He followed the same methods as Solounias et al. (1988) and

60

Solounias and Moelleken (1993) to discriminate snout varieties, adding two additional

comparative metrics based on the quality of the specimens. This study is intriguing, as

obviously most dinosaurs cannot be fitted into the regular classes of browsers and grazers

due to the general lack of contemporary grasslands. Nevertheless, the additional dimension

of browsing height allows comparisons to be drawn with extant organisms (i.e., ungulates),

but applied to different ecological hypotheses. Whitlock (2011) draws comparisons with

Carrano et al. (1999), in that different groups of sauropods and hadrosaurs are analogous in

their feeding styles, despite their phylogenetic and ecological distance. Carrano et al. (1999)

in an analysis of muzzle shape (using width as a proxy) recovered a functional dichotomy

between typically dimorphic lambeosaurine and monomorphic hadrosaurine hadrosaurs, in

that the former have narrower snouts (premaxillae) indicative of selective browsing, and

the latter having broader snouts for non-selective browsing. This hypothesized shape-based

dichotomy was not recovered in this study, despite the use of a similar range of hadrosaurs.

The results obtained in Whitlock (2011) are more applicable to the patterns detected by

this study. Within sauropods, specifically the clade Diplodocoidea, a functional dichotomy

was resolved with respect to snout shape, relating to both selectivity and browsing height,

with the simple use of ‘square’ and ‘round’ shapes defining these feeding strategies.

Diplodocoids with a ‘round’ snout shape are considered by Whitlock (2011) as mid-height

canopy browsers with a selective diet. Those with ‘square’ snouts were interpreted as

ground-level non-selective browsers. Application of these inferences to ornithopods is

somewhat problematic, given the disparity in body size between the two groups

(ornithopods were typically considerably smaller). However, selectivity and browsing height

are largely independent factors – just because an organism browses at a mid-level height, it

does not necessarily mean that they were selective. The significant aspect of this analysis is

that functional groups, relating to two independent dimensions of feeding style, are

strongly associated with snout shape. Applying these inferences to the current

investigation, it is plausible that ornithopods with more pointed snouts (i.e., the

heterodontosaur- and hypsilophodont-grade species) had selective diets, but at a browsing

height closer to ground level befitting their typically small stature. Furthermore, hadrosaurs

can be considered to be ground-level non-selective browsers, a somewhat counter-intuitive

61

deduction given their increased height. This could further support the notion that

hadrosaurs were facultatively bipedal, adopting a quadrupedal stance for ground-level

foraging (see Sellers et al. 2009).

The relation of dinosaurian feeding mechanisms to contemporary floral diversity has been a

focus of study for many years (see Butler et al. 2009). Butler et al. (2009), using a large

occurrence database of all known Cretaceous plants and herbivorous dinosaurs, found that

there is no correlation between the relative diversity of one particular dinosaurian clade

(e.g., Ornithopoda, Sauropoda) to that of contemporary floras, specifically focussing on

angiosperms. This is consistent with the underlying co-radiation hypothesis between

dinosaurs and angiosperms (the proposition that a ‘faunal changeover’ from high-browsers

to low-browsers at the Jurassic-Cretaceous boundary drove the radiation of early

angiosperms) within a phylogenetic framework; i.e., can the relative phylogenetic diversity

of any herbivorous dinosaur clade be associated with a concurrent variation in the diversity

of early flowering plants. Nevertheless, this interesting result does not constitute a test of

“co-evolution” (see Sander et al. (2010), p. 352); it is a test of co-radiation, based on

analysis of relative diversity, of which co-evolution is a more intricate detail within,

consisting of the synchronized evolution of adaptive traits in, for example, competitive

organisms or those with predator-prey interactions (i.e., a strong ecological coupling).

Results by Butler et al. (2009) were non-significant for all dinosaurian clades. However,

Leckey (2004) found a strong correlation between end-Cretaceous North American

ornithischians (including ornithopods) and angiosperms. Butler and Barrett (2008) found

that both hadrosaurids and non-hadrosaurid ornithopods are significantly correlated with

Cretaceous marine sediments (albeit within coarse sedimentological and taxonomic

groupings), representing environments such as coastal plain. However, ornithopods also

occur within terrestrial sediments (e.g., Tenontosaurus is associated with Early Cretaceous

lacustrine and fluvial sediments). This supports the view advocated by Sander et al. (2010)

that ornithopods deliberately segregated themselves spatially from direct competition with

contemporary sauropodomorphs. But there is no evidence to indicate this is a secondary

consequence of an ornithopod association with angiosperms, as the authors speculate.

62

The earliest angiosperm macrofossils are rare, and occur in Lower Aptian to Lower

Cenomanian (125-96Ma) sequences from the United States mid-Atlantic coast (Hochuli et

al., 2006). Within this sequence, the angiosperms become increasingly abundant through

time, in facies representing highly-disturbed riparian environments (Royer et al., 2010).

These earliest angiosperms are interpreted as rapidly growing weedy shrubs and herbs

(Royer et al., 2010). Contiguous ornithopods, as revealed by this investigation, typically

possessed distally rounded or pointed snouts, belonging to iguanodontid- or

hypsilophodont-grade species respectively. These forms were succeeded in most cases by

hadrosaurs during the Upper Cretaceous, representing a turnover in body size and feeding

strategies. In agreement with Williams et al., (2009), it is suggested here that hadrosaurs

may have been ground-level feeders. If this is indeed the case, then what this observation

represents is an ecological shift from smaller, ‘browsing’ ornithopods, with a transitional

and experimental phase in iguanodontid feeding strategies, the timing of which coincides

with initial angiosperm diversification, followed by hadrosaurs with a high consumption

rate of ground-level forage.

According to Butler et al. (2009), angiosperm diversification increased significantly during

the Santonian-Maastrichtian to a similar degree as the initial Albian-Cenomanian radiation.

It is possible that this second radiation, which coincides with increasing hadrosaur diversity,

is related to this changeover in feeding strategy. During the latter half of the Upper

Cretaceous hadrosaurs were dominant terrestrial herbivores, with a fairly cosmopolitan

distribution. As angiosperm diversity has often been linked theoretically with increased

environmental disturbance (see Butler et al. 2009), which plausibly could result from

increased ‘grazing’ by hadrosaurs, it is possible that increasing angiosperm diversity during

the Upper Cretaceous may be closely coupled with increasing hadrosaur diversity

(conforming to Leckey, 2004), and concurrent changes in feeding strategy accompanying

this. However, there is a distinct paucity of macrofossils for both hadrosaurs and

angiosperms during the Turonian-Santonian periods (Butler et al., 2009). As a result, the

exact timing of this turnover and diversification of both hadrosaurs and angiosperms is

poorly understood on a spatiotemporal scale. What would be worthwhile is the mapping of

63

snout shapes on to all known ornithopod occurrences, following the methods of Butler et

al. (2009), and observing not just the changes in relative diversification patterns, but seeing

if angiosperm diversity patterns can be spatiotemporally linked with variations in

ornithopodan feeding strategies, as revealed from snout profile shape.

Ornithopods are unique among all other Ornithischians in that it is likely they favoured a

grinding mechanism using complex ‘dental batteries’ as opposed to slicing with pointed

‘beaks’, except for perhaps some plesiomorphic species and ceratopsians (Bell et al., 2009).

This complexity of the masticatory system is conceivably a mechanical adaptation relating

to increased consumption of low-quality forage, which at ground level will have included

minor volumes of grit, and possible silicophytoliths if early grasses were consumed too

(Williams et al., 2009). Future analysis of all ornithischian clades should further shed light

on the feeding strategies of contemporary and ecologically significant organisms, and how

they interacted in a more subtle manner with their surrounding ecosystems.

64

6.0 Conclusions

Using a two-dimensional representation of the ruminant snout in ventral aspect, it is found

in this study there was no relation between snout shape and feeding strategy within a

highly diverse sample of the major ruminant clades (i.e., rejection of the primary hypothesis

and acceptance of both the null and alternative hypotheses, conforming largely to Pérez-

Barbería and Gordon, 1999). The lack of between-group discrimination was statistically

significant in most cases as assessed by a likelihood ratio test. These results are not

believed to be a phylogenetic artefact, contra Raia et al. (2010) among others. It is also

found that previously used categorisations relating snout shape to feeding strategy are

inadequate to in their descriptions of the full range of exhibited morphological variation

(i.e., ‘browsers’ do not specifically have ‘pointed’ snouts, and ‘browsers’ do not have ‘blunt’

snouts as previously postulated). The geometric complexity is more extensive than this, and

forms a continuum of shape variation (figs 13, 28 and 29). These results suggest that

attempts to place arbitrary thresholds on other related factors involved in feeding are

problematic and should be discontinued (following the recommendations of Gordon and

Illius, 1994). For example, attempting to classify ruminants based on various subjective

thresholds for their percentage of grass consumption seems highly suspect (see

Introduction). In light of this analysis, results obtained by Janis et al. (2010) - that intake

rate forces covariation in the anatomical strength of the mandible - should be reanalysed to

determine whether grazing ruminants have a more robust masticatory apparatus than

browsing ruminants. It is proposed here, in an manner analogous to that of Codron et al.

(2007), that ruminant diets represent a continuum with variation explicitly occurring on a

spatiotemporal scale for all feeding strategies, with individual strategies varying in a

homoplastic manner that is inconsistent with phylogenetic relation.

The fact that feeding strategies were not demonstrated to be associated with snout shape

in this investigation should be a point of concern for future ecological studies involving

ruminants. Accordingly, it is recommended snout shape should be subjected to further

study to determine whether it constitutes a morphological feature capable of delimiting

browsing and grazing ruminants (e.g., Janis and Ehrhardt, 1998). Reconstruction of

65

palaeodiets based on snout shape should similarly be questioned (Solounias et al., 1988;

Solounias and Moelleken, 1993), given that this appears to be an inadequate proxy for

extant ruminants. It is conceivable that the results here a product of the lack of consistency

in defining functional feeding groups for ruminants with respect to other

morphophysiological traits. The functional significance of snout shape in both intake rate

and selectivity is not questioned. However, the results of this study imply that closer

inspection of this relation is required, with intake rate and selectivity being related to snout

shape within an analytically robust statistical framework.

Following the ecological classifications proposed in Whitlock (2011) regarding diplodocoid

sauropods, the results for the ornithopod data set reveal stronger patterns relating snout

morphology to feeding style than those found in ruminants. Hypsilophodont- and

heterodontosaur-grade species are largely consistent with a ‘pointed’ snout geometry,

reflecting a selective diet, close to ground-level given their typical size. Patterns in several

ornithopod clades (e.g., Dryosauridae, Camptosauridae) are difficult to discern due to low

sampling frequency. Iguanodonts appear to have gone through a transitional and

experimental phase, with a variety of snout morphologies reflecting adaptation to

numerous feeding roles. Hadrosaurs took on the role of non-selective ground-level

‘grazers’, reflected in their widened and distally flattened snout morphologies, an assertion

corroborated by analysis of tooth microwear in hadrosaurs (Williams et al., 2009). Previous

assertions that hadrosaurs and ruminants are ecological parallels are challenged based on

the disparate snout shapes exhibited by the two groups (Fig. 30). However, there are two

issues with these results. It is likely that taphonomic deformation anisotropically modified

the shape of several of the specimens (Fig. 36), creating lateral distortions in the snout

profile shape. It may be feasible to remove these potentially confounding artefacts to

reconstruct the true specimen profile for future analyses. Also, little is known about the

ontogenetic stage of majority of the specimens. If premaxilla shape varies in an allometric

manner, this could account for some aspects of the patterns observed here. Resolution of

this issue will require careful consideration in future analyses of morphological shape

variation. Nevertheless, it appears in the dataset investigated here that genera were

66

taxonomically well constrained. This suggests ontogeny is not affecting the results to a

significant degree (except perhaps in the overlapping hadrosaur-iguanodont shape

domain).

Furthermore, the phylogenetic and ecological turnover between iguanodontians and

hadrosaurians may be associated with a secondary burst of angiosperm diversification

during the Upper Cretaceous (approximately Santonian age). The theoretical backing for

this putative linkage is that it is believed angiosperms flourished initially in a highly

disturbed environment, with which the transition in feeding strategy for hadrosaurs may be

associated (i.e., hadrosaurs were megaherbivores with a low-selectivity and high intake rate

to maintain their increasing body size). This secondary hypothesis requires an empirical

synthesis between previous studies (e.g., Butler and Barrett, 2008; Butler et al., 2009) to

determine whether this trait in hadrosaurs can be correlated within both environmental

and spatiotemporal parameters.

Following this study, future investigations could follow many routes to answer a number of

important ecological questions regarding the evolutionary histories of both ruminants and

ornithopods. Snout shape was found to be a poor basis for discriminating between feeding

strategies in ruminants. Subsequently, study is needed regarding the extent to which snout

shape can be associated with other digestive and ingestive parameters, and to other

morphophysiological factors. If other parameters are found to be related to feeding

strategy, the issue then becomes whether these factors covary equally, or force

modification upon each other?

The phylogenetic comparisons drawn in this study were predominantly qualitative. What is

undoubtedly required is the dissection of recovered signals to determine what proportion

of trait covariation can be explained by phylogenetic relationships (i.e., morphological

similarity based on common ancestry; e.g., Figuerido et al., 2010; Raia et al., 2010).

Applicable methods include the phylogenetic GLS (general least squares) model, which has

gained increasing interest in the fields of macroecology and macroevolution (e.g., Cardillo

et al., 2010). Furthermore, if singular or multiple functional traits are found to be

67

phylogenetic artefacts, it could be possible to track the sequence of acquisition, and

therefore trace the functional and ecological histories of ruminants. In addition to

phylogenetic correlation, other factors such as ontogeny and sexual dimorphism should be

scrutinised within a statistical framework to detect potential allometric variation, and

possible synchronisation of trait acquisition and evolution patterns between sexes.

68

7.0 Acknowledgements

First and foremost, I would like to extend my gratitude to Norman MacLeod (Natural

History Museum, London), for helping me develop and improve this project from day one,

constantly providing technical assistance on many of the more difficult aspects of geometric

morphometrics, and also providing the initial ornithopod profile outlines, self-made

analytical software, and a laboratory with which to work in. I am also indebted to Roberto

Portela Miguez (Natural History Museum, London), for allowing me access to specimens on

numerous occasions, in spite of my terrible organisational skills. For additional ornithopod

material, I would also like to extend my appreciations to Clint Boyd (University of Texas),

Andrew McDonald (University of Pennsylvania), and Richard Butler (Bayerische

Staatssammlung für Paläontologie und Geologie). Finally, I would like to thank Marcus

Clauss (University of Zurich) for providing several difficult to obtain documents used in this

study.

69

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9.0 Appendices

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Po

inte

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Inte

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Var

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Men

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nd P

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st (

20

06

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mo

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ni

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an (

19

89

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lunt

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Bo

vid

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pin

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tra

gus

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min

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% b

row

seG

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on

and

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us (

19

96

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lunt

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nt-c

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Bo

vid

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cho

tra

gus

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enth

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ni

Bro

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ario

usM

end

oza

and

Pal

mq

vist

(2

006

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lunt

Blu

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vid

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phu

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ag

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mel

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term

edia

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s et

al.

(2

010

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Ta

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Inte

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Var

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Men

do

za a

nd P

alm

qvi

st (

20

06

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lunt

Blu

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r

Bo

vid

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nae

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race

rus

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ad

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dont

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s et

al.

(2

010

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Bo

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hu

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Inte

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Var

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Men

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alm

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st (

20

06

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lunt

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ni

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Men

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nd P

alm

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st (

20

06

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lunt

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Bo

vid

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gel

ap

hu

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rus

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(2

010

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Bo

vid

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nae

Tra

gel

ap

hu

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row

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ont

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(2

010

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Men

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alm

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st (

20

06

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hu

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term

edia

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s et

al.

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010

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ap

hu

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rep

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s-

Bro

wse

rV

ario

usM

end

oza

and

Pal

mq

vist

(2

006

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lunt

Blu

nt-c

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vid

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Inte

rmed

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Var

ious

Men

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za a

nd P

alm

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st (

20

06

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lunt

Blu

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vid

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lop

hina

eC

eph

alo

phu

sd

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alis

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row

ser

Bra

chyd

ont

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s et

al.

(2

010

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ifer

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% g

rass

esC

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s et

al.

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009

c)P

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ted

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inte

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ex

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vid

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elli

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eric

affin

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ferr

edP

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ted

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Unk

now

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laus

et

al.

(2

002

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ted

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inte

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Bo

vid

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lop

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alo

phu

sn

ate

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sis

na

tele

nsi

sB

row

ser

1%

gra

sses

Cla

uss

et a

l. (

20

09

c)B

lunt

Blu

nt-c

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ave

Bo

vid

aeC

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lop

hina

eC

eph

alo

phu

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iger

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row

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Bra

chyd

ont

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s et

al.

(2

010

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ted

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vid

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eric

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ityIn

ferr

edP

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vid

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fila

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ncen

trat

e se

lect

or

Ho

ffm

an (

19

89

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oin

ted

Po

inte

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onv

ex

87

Fam

ily

Subfa

mily

Genus

Speci

es

Sub-s

peci

es

Eco

logy

Cri

teri

on

Refe

rence

Shape I

Shape I

I

Bovi

dae

Cep

halo

phi

nae

Cep

halo

phus

silv

icult

or

rufi

cris

tus

Bro

wse

rG

ener

ic a

ffin

ityIn

ferr

edP

oin

ted

Poin

ted-c

onv

ex

Bovi

dae

Cep

halo

phi

nae

Cep

halo

phus

zebra

-B

row

ser

Gen

eric

affin

ityIn

ferr

edP

oin

ted

Poin

ted-c

onc

ave

Bovi

dae

Cep

halo

phi

nae

Syl

vic

apra

gri

mm

ia-

Fru

givo

reV

ario

usM

endoza

and

Pal

mqvi

st (

2006)

Poin

ted

Poin

ted-l

inea

r

Bovi

dae

Hip

potr

agin

aeA

ddax

naso

macu

latu

s-

Gra

zer

80%

gra

ssC

laus

s et

al.

(2009c)

Poin

ted

Poin

ted-c

onv

ex

Bovi

dae

Hip

potr

agin

aeH

ippotr

agus

equin

us

-G

raze

rH

ypso

dont

yS

olo

unia

s et

al.

(2010)

Blu

ntB

lunt

-conc

ave

Bovi

dae

Hip

potr

agin

aeH

ippotr

agus

nig

er-

Gra

zer

Var

ious

Men

doza

and

Pal

mqvi

st (

2006)

Blu

ntB

lunt

-conc

ave

Bovi

dae

Hip

potr

agin

aeO

ryx

bei

sabei

saG

raze

r>

75%

gra

sses

Gord

on

and I

llius

(1996)

Blu

ntB

lunt

-conc

ave

Bovi

dae

Hip

potr

agin

aeO

ryx

gaze

lla

-G

raze

r82%

gra

sses

Cla

uss

et a

l. (

2009c)

Blu

ntB

lunt

-conc

ave

Bovi

dae

Hip

potr

agin

aeO

ryx

leuco

ryx

-G

raze

rG

rass

/roug

hage

eat

ers

Hoffm

an (

1989)

Blu

ntB

lunt

-conv

ex

Bovi

dae

Red

unci

nae

Kobus

def

ass

a-

Gra

zer

Hyp

sodont

yS

olo

unia

s et

al.

(2010)

Poin

ted

Poin

ted-c

onc

ave

Bovi

dae

Red

unci

nae

Kobus

ellipsi

pry

mnus

-G

raze

rH

ypso

dont

yS

olo

unia

s et

al.

(2010)

Blu

ntB

lunt

-conv

ex

Bovi

dae

Red

unci

nae

Kobus

kob

leuco

tis

Gra

zer

Var

ious

Men

doza

and

Pal

mqvi

st (

2006)

Blu

ntB

lunt

-conc

ave

Bovi

dae

Red

unci

nae

Kobus

lech

e-

Gra

zer

Hyp

sodont

yS

olo

unia

s et

al.

(2010)

Blu

ntB

lunt

-conc

ave

Bovi

dae

Red

unci

nae

Kobus

meg

ace

ros

-G

raze

rG

ener

ic a

ffin

ityIn

ferr

edB

lunt

Blu

nt-c

onc

ave

Bovi

dae

Red

unci

nae

Kobus

vard

onii

-G

raze

rV

ario

usM

endoza

and

Pal

mqvi

st (

2006)

Poin

ted

Poin

ted-c

onc

ave

Bovi

dae

Red

unci

nae

Pel

eaca

pre

olu

s-

Bro

wse

r7%

gra

sses

Cla

uss

et a

l. (

2009c)

Poin

ted

Poin

ted-c

onc

ave

Bovi

dae

Red

unci

nae

Red

unca

aru

ndin

um

-F

rugi

vore

Var

ious

Men

doza

and

Pal

mqvi

st (

2006)

Blu

ntB

lunt

-conc

ave

Bovi

dae

Red

unci

nae

Red

unca

fulv

uro

fula

-In

term

edia

teV

ario

usM

endoza

and

Pal

mqvi

st (

2006)

Blu

ntB

lunt

-conc

ave

Bovi

dae

Red

unci

nae

Red

unca

redunca

-G

raze

rH

ypso

dont

yS

olo

unia

s et

al.

(2010)

Blu

ntB

lunt

-conc

ave

Cer

vidae

Cap

reolin

aeA

lces

alc

es-

Bro

wse

r<

20%

gra

sses

Codro

n an

d C

laus

s (2

010)

Blu

ntB

lunt

-conc

ave

Cer

vidae

Cap

reolin

aeA

lces

pulm

atu

s-

Bro

wse

rC

onc

entr

ate

sele

ctor

Hoffm

an (

1989)

Bun

tB

lunt

-conc

ave

Cer

vidae

Cap

reolin

aeB

last

oce

ras

bez

oart

icus

-In

term

edia

teG

ener

ic a

ffin

ityIn

ferr

edB

lunt

Blu

nt-c

onc

ave

Cer

vidae

Cap

reolin

aeB

last

oce

ras

dic

hoto

mus

-In

term

edia

te24%

gra

sses

Cla

uss

et a

l. (

2009c)

Blu

ntB

lunt

-lin

ear

Cer

vidae

Cap

reolin

aeC

apre

olu

sca

pre

olu

s-

Bro

wse

r<

20%

gra

sses

Codro

n an

d C

laus

s (2

010)

Poin

ted

Poin

ted-l

inea

r

Cer

vidae

Cap

reolin

aeH

ippoca

mel

us

anti

sensi

s-

Inte

rmed

iate

Gen

eric

affin

ityIn

ferr

edB

lunt

Blu

nt-c

onv

ex

Cer

vidae

Cap

reolin

aeM

aza

ma

am

eric

ana

-B

row

ser

1%

gra

sses

Cla

uss

et a

l. (

2009c)

Blu

ntB

lunt

-lin

ear

Cer

vidae

Cap

reolin

aeM

aza

ma

gouazo

ubia

-B

row

ser

Gen

eric

affin

ityIn

ferr

edP

oin

ted

Poin

ted-l

inea

r

Cer

vidae

Cap

reolin

aeO

doco

ileu

shem

ionus

-B

row

ser

Unk

now

nC

laus

s et

al.

(2002)

Blu

ntB

lunt

-lin

ear

Cer

vidae

Cap

reolin

aeO

doco

ileu

svir

gin

ianus

-B

row

ser

9%

gra

sses

Cla

uss

et a

l. (

2009c)

Blu

ntB

lunt

-conv

ex

Cer

vidae

Cap

reolin

aeO

zoto

cera

sbez

oart

icus

-In

term

edia

teU

nkno

wn

Cla

uss

et a

l. (

2002)

Blu

ntB

lunt

-conc

ave

Cer

vidae

Cap

reolin

aeP

udu

puda

-B

row

ser

3%

gra

sses

Cla

uss

et a

l. (

2009c)

Poin

ted

Poin

ted-c

onv

ex

Cer

vidae

Cap

reolin

aeR

angif

erta

randus

-In

term

edia

te36%

gra

sses

Cla

uss

et a

l. (

2009c)

Poin

ted

Poin

ted-c

onc

ave

Cer

vidae

Cer

vina

eA

xis

axis

-In

term

edia

te70%

gra

sses

Cla

uss

et a

l. (

2009c)

Poin

ted

Poin

ted-c

onc

ave

88

Fam

ily

Subfa

mily

Genus

Speci

es

Sub-s

peci

es

Eco

logy

Cri

teri

on

Refe

rence

Shape I

Shape I

I

Cer

vidae

Cer

vina

eC

ervus

axis

ceyl

onen

sis

Inte

rmed

iate

Gen

eric

affin

ityIn

ferr

edB

lunt

Blu

nt-c

onc

ave

Cer

vidae

Cer

vina

eC

ervus

duvauce

li-

Inte

rmed

iate

Mes

odont

yS

olo

unia

s et

al.

(2010)

Poin

ted

Poin

ted-c

onc

ave

Cer

vidae

Cer

vina

eC

ervus

elaphus

-In

term

edia

te20-8

0%

gra

sses

Codro

n an

d C

laus

s (2

010)

Blu

ntB

lunt

-conc

ave

Cer

vidae

Cer

vina

eC

ervus

eldii

eldii

Inte

rmed

iate

Unk

now

nC

laus

s et

al.

(2002)

Poin

ted

Poin

ted-l

inea

r

Cer

vidae

Cer

vina

eC

ervus

kuhli

-In

term

edia

teG

ener

ic a

ffin

ityIn

ferr

edB

lunt

Blu

nt-c

onc

ave

Cer

vidae

Cer

vina

eC

ervus

nip

pon

-In

term

edia

te50%

gra

sses

Cla

uss

et a

l. (

2009c)

Blu

ntB

lunt

-conc

ave

Cer

vidae

Cer

vina

eC

ervus

schom

burg

ki

-In

term

edia

teG

ener

ic a

ffin

ityIn

ferr

edB

lunt

Blu

nt-c

onc

ave

Cer

vidae

Cer

vina

eC

ervus

tim

ore

nsi

s-

Inte

rmed

iate

Unk

now

nC

laus

s e

t al.

(2002)

Poin

ted

Poin

ted-c

onv

ex

Cer

vidae

Cer

vina

eC

ervus

unic

olo

rbro

okei

Inte

rmed

iate

Mes

odont

yS

olo

unia

s et

al.

(2010)

Blu

ntB

lunt

-conc

ave

Cer

vidae

Cer

vina

eD

am

adam

a-

Inte

rmed

iate

Unk

now

nF

letc

her

et a

l. (

2010)

Blu

ntB

lunt

-conc

ave

Cer

vidae

Cer

vina

eE

laphuru

sdavid

ianus

-G

raze

r75%

gra

sses

Cla

uss

et a

l. (

2009c)

Blu

ntB

lunt

-conc

ave

Cer

vidae

Hyd

ropotin

aeH

ydro

podus

iner

mis

-In

term

edia

te50%

gra

sses

Cla

uss

et a

l. (

2009c)

Poin

ted

Poin

ted-c

onv

ex

Cer

vidae

Mun

tiaci

nae

Ela

phodus

cephalo

phus

-B

row

ser

Unk

now

nC

laus

s et

al.

(2002)

Poin

ted

Poin

ted-c

onv

ex

Cer

vidae

Mun

tiaci

nae

Munti

acu

scr

inif

rons

-B

row

ser

Gen

eric

affin

ityIn

ferr

edP

oin

ted

Poin

ted-l

inea

r

Cer

vidae

Mun

tiaci

nae

Munti

acu

sm

untj

ak

vagin

alis

Bro

wse

r10%

gra

sses

Cla

uss

et a

l. (

2009c)

Poin

ted

Poin

ted-c

onv

ex

Cer

vidae

Mun

tiaci

nae

Munti

acu

sre

eves

ire

eves

iB

row

ser

Gen

eric

affin

ityIn

ferr

edB

lunt

Blu

nt-l

inea

r

Giraf

fidae

-G

iraff

aca

mel

opard

alis

-B

row

ser

>75%

bro

wse

Gord

on

and I

llius

(1996)

Poin

ted

Poin

ted-c

onc

ave

Mosc

hidae

-M

osc

hus

mosc

hif

erous

-In

term

edia

teG

ener

ic a

ffin

ityIn

ferr

edB

lunt

Blu

nt-l

inea

r

Tra

gulid

ae-

Tra

gulu

sja

vanic

us

insu

lari

sB

row

ser

Unk

now

nF

letc

her

et a

l. (

2010)

Poin

ted

Poin

ted-c

onv

ex

Tra

gulid

ae-

Tra

gulu

skanch

ilum

bri

nus

Bro

wse

rG

ener

ic a

ffin

ityIn

ferr

edP

oin

ted

Poin

ted-c

onv

ex

Tra

gulid

ae-

Tra

gulu

snapu

-B

row

ser

Gen

eric

affin

ityIn

ferr

edP

oin

ted

Poin

ted-l

inea

r

Ap

pen

dix

1 –

Ru

min

ant

sam

ple

lis

t fo

r th

is s

tud

y. T

axo

no

mic

det

ails

wer

e ex

trac

ted

fro

m W

ilso

n a

nd

Co

le (

20

00

). T

he

eco

logi

cal

det

ails

we

re e

xtra

cted

fro

m a

ran

ge o

f so

urc

es;

gen

eric

aff

init

y as

a c

rite

rio

n s

ign

ifie

s as

sign

men

t to

a p

arti

cula

r ec

olo

gy b

ased

up

on

det

ails

re

gard

ing

spec

ies

wit

hin

th

e sa

me

gen

us.

Ass

ign

ed

shap

e gr

ou

pin

gs a

re d

iscu

sse

d in

th

e te

xt.

89

Speci

men I

DT

axonom

ic G

roup

Genus

Speci

es

Refe

rence

Age

Shape I

Shape I

I

YP

M 1

880

Cam

pto

saur

idae

Cam

pto

sauru

sdis

par

A. M

cDona

ldU

pper

Jur

assi

cB

lunt

Blu

nt-l

inea

r

CM

3392

Dry

osa

urid

aeD

ryosa

uru

s alt

us

A. M

cDona

ldU

pper

Jur

assi

cB

lunt

Blu

nt-c

onc

ave

N/A

Dry

osa

urid

aeD

ryosa

uru

s le

ttow

vorb

ecki

Gal

ton

(1983)

Upper

Jur

assi

cB

lunt

Blu

nt-c

onc

ave

AM

NH

5730

Had

rosa

urid

aeA

nato

tita

nco

pei

N. M

acle

od; A

. M

cDona

ldU

pper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

NM

C 8

893

Had

rosa

urid

aeB

rach

ylophosa

uru

sca

naden

sis

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

AM

NH

5338

Had

rosa

urid

aeC

ory

thosa

uru

sca

suari

us

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

AM

NH

5382

Had

rosa

urid

aeC

ory

thosa

uru

sca

suari

us

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

CM

11375

Had

rosa

urid

aeC

ory

thosa

uru

sca

suari

us

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

NM

C 8

433

Had

rosa

urid

aeC

ory

thosa

uru

sca

suari

us

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

RO

M 1

933

Had

rosa

urid

aeC

ory

thosa

uru

sca

suari

us

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

RO

M 1

947

Had

rosa

urid

aeC

ory

thosa

uru

sca

suari

us

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

RO

M 7

59

Had

rosa

urid

aeC

ory

thosa

uru

sca

suari

us

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

AM

NH

5359

Had

rosa

urid

aeC

ory

thosa

uru

sca

suari

us

N. M

acle

od; A

. M

cDona

ldU

pper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

AM

NH

5060

Had

rosa

urid

aeE

dm

onto

sauru

sre

galis

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

Chi

cago

I15

Had

rosa

urid

aeE

dm

onto

sauru

sre

galis

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

NM

C 2

288

Had

rosa

urid

aeE

dm

onto

sauru

s re

galis

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

NS

R4036

Had

rosa

urid

aeE

dm

onto

sauru

s re

galis

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

AM

NH

5465

Had

rosa

urid

aeG

ryposa

uru

s la

tiden

sN

. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

NM

C 2

278

Had

rosa

urid

aeP

rosa

uro

lophus

nota

bilis

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

NM

C 2

246

Had

rosa

urid

aeH

ypacr

osa

uru

salt

ispin

us

N. M

acle

od

Upper

Cre

tace

ous

Poin

ted

Poin

ted-c

onc

ave

NM

C 2

247

Had

rosa

urid

aeH

ypacr

osa

uru

salt

ispin

us

N. M

acle

od

Upper

Cre

tace

ous

Poin

ted

Blu

nt-c

onc

ave

RO

M 7

82

Had

rosa

urid

aeL

am

beo

sauri

ne

indet

.N

. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

US

NM

16600

Had

rosa

urid

aeL

am

beo

sauri

ne

indet

.N

. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

AM

NH

5340

Had

rosa

urid

aeL

am

beo

sauru

sla

mbei

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

NM

C 8

703

Had

rosa

urid

aeL

am

beo

sauru

sla

mbei

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

P67 9

166

Had

rosa

urid

aeL

am

beo

sauru

sla

mbei

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-lin

ear

RO

M 1

218

Had

rosa

urid

aeL

am

beo

sauru

sla

mbei

N. M

acle

od

Upper

Cre

tace

ous

Poin

ted

Poin

ted-c

onc

ave

RO

M 7

58

Had

rosa

urid

aeL

am

beo

sauru

sla

mbei

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

RO

M 7

94

Had

rosa

urid

aeL

am

beo

sauru

sla

mbei

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

TM

P P

78.1

6.1

Had

rosa

urid

aeL

am

beo

sauru

sla

mbei

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

US

NM

IV

Had

rosa

urid

aeL

am

beo

sauru

sla

mbei

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

YP

M 3

222

Had

rosa

urid

aeL

am

beo

sauru

sla

mbei

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

90

Appendix 2 – Ornithopod sample list for this study (including ‘Heterodontosauridae’). Names refer

to people who personally provided images for analysis. Taxonomic groups are discussed in the

text. Shape categories were assigned in the same manner as for the ruminants.

Speci

men I

DT

axonom

ic G

roup

Genus

Speci

es

Refe

rence

Age

Shape I

Shape I

I

PU

22405

Had

rosa

urid

aeM

aia

saura

pee

ble

soru

mN

. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

MN

HM

GD

F 3

00

Had

rosa

urid

aeO

ura

nosa

uru

snig

erie

nsi

sN

. M

acle

od

Low

er C

reta

ceous

Blu

ntB

lunt

-conc

ave

IVM

C 2

277

Had

rosa

urid

aeP

rosa

uro

lophus

maxim

us

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

NM

C 2

970

Had

rosa

urid

aeP

rosa

uro

lophus

maxim

us

N. M

acle

od

Upper

Cre

tace

ous

Poin

ted

Poin

ted-c

onv

ex

PU

14970

Had

rosa

urid

aeP

rosa

uro

lophus

maxim

us

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conv

ex

R3386/7

Had

rosa

urid

aeT

elm

ato

sauru

s tr

anss

ylvanic

us

Wei

sham

pel

et

al.

(1993)

Upper

Cre

tace

ous

Blu

ntB

lunt

-conc

ave

-H

eter

odont

osa

urid

aeA

gilis

auru

slo

uder

back

iR

. B

utle

rM

iddle

Jur

assi

cP

oin

ted

Poin

ted-c

onc

ave

SA

M K

337

Het

erodont

osa

urid

aeH

eter

odonto

sauru

stu

cki

N. M

acle

od

Low

er J

uras

sic

Poin

ted

Poin

ted-c

onc

ave

SA

M K

1332

Het

erodont

osa

urid

aeH

eter

odonto

sauru

s tu

cki

N. M

acle

od

Low

er J

uras

sic

Poin

ted

Poin

ted-c

onc

ave

JLU

M L

0204-Y

-23

Hyp

silo

pho

dont

idae

Changch

unsa

uru

sparv

us

Liy

ong

et

al.

(2010)

Low

er C

reta

ceous

Poin

ted

Poin

ted-c

onv

ex

IGM

100/2

017

Hyp

silo

pho

dont

idae

Haya

gri

va

Mak

ovi

cky

et a

l. (

2011)

Upper

Cre

tace

ous

Poin

ted

Poin

ted-l

inea

r

R2477

Hyp

silo

pho

dont

idae

Hyp

silo

phodon

foxii

Gal

ton

(1974)

Low

er C

reta

ceous

Poin

ted

Poin

ted-c

onv

ex

R196

Hyp

silo

pho

dont

idae

Hyp

silo

phodon

foxii

N. M

acle

od

Low

er C

reta

ceous

Poin

ted

Poin

ted-c

onv

ex

R197

Hyp

silo

pho

dont

idae

Hyp

silo

phodon

foxii

N. M

acle

od

Low

er C

reta

ceous

Poin

ted

Poin

ted-c

onv

ex

IVP

P V

12529

Hyp

silo

pho

dont

idae

Jeholo

sauru

ssh

angyu

anen

sis

Bar

rett a

nd H

an (

2009)

Low

er C

reta

ceous

Poin

ted

Poin

ted-c

onv

ex

MO

R 1

636a

Hyp

silo

pho

dont

idae

Ory

ctodro

meu

scu

bic

ula

ris

C. B

oyd

Upper

Cre

tace

ous

Poin

ted

Poin

ted-l

inea

r

4 H

AI

7A

Hyp

silo

pho

dont

idae

Thes

celo

sauru

sneg

lect

us

N. M

acle

od

Upper

Cre

tace

ous

Blu

ntB

lunt

-conv

ex

NC

SM

15728

Hyp

silo

pho

dont

idae

Thes

celo

sauru

ssp

.C

. B

oyd

Upper

Cre

tace

ous

Poin

ted

Poin

ted-c

onv

ex

MC

Z 4

392

Hyp

silo

pho

dont

idae

Zep

hyr

osa

uru

ssc

haff

iC

. B

oyd

Low

er C

reta

ceous

Poin

ted

Poin

ted-c

onv

ex

SD

SM

8691

Igua

nodont

iaD

akata

don

lakota

ensi

sN

. M

acle

od; A

. M

cDona

ldL

ow

er C

reta

ceous

Blu

ntB

lunt

-conv

ex

FP

DM

-V-4

0-3

Igua

nodont

iaF

ukuis

auru

ste

tori

ensi

sK

obay

ashi

and

Azu

ma

(2003)

Low

er C

reta

ceous

Blu

ntB

lunt

-conv

ex

BM

NH

9764

Igua

nodont

iaM

ante

llis

auru

sath

erfi

elden

sis

N. M

acle

od

Low

er C

reta

ceous

Blu

ntB

lunt

-conv

ex

IRS

N B

II

30A

Igua

nodont

iaIg

uanodon

ber

nis

sart

ensi

sN

. M

acle

od

Low

er C

reta

ceous

Blu

ntB

lunt

-lin

ear

IRS

NB

1457

Igua

nodont

iaIg

uanodon

ber

nis

sart

ensi

sN

. M

acle

od

Low

er C

reta

ceous

Blu

ntB

lunt

-conc

ave

IRS

NB

1536

Igua

nodont

iaIg

uanodon

ber

nis

sart

ensi

sN

. M

acle

od

Low

er C

reta

ceous

Blu

ntB

lunt

-conc

ave

IRS

NB

II

35A

Igua

nodont

iaIg

uanodon

ber

nis

sart

ensi

sN

. M

acle

od

Low

er C

reta

ceous

Blu

ntB

lunt

-conc

ave

FW

MS

H 9

3B

1Ig

uano

dont

iaT

enonto

sauru

sdoss

iW

inkle

r e

t al.

(1997)

Low

er C

reta

ceous

Poin

ted

Poin

ted-c

onc

ave

YP

M 5

456

Igua

nodont

iaT

enonto

sauru

sti

llet

oru

mO

stro

m (

1970);

A. M

cDona

ldL

ow

er C

reta

ceous

Blu

ntB

lunt

-conc

ave

AM

NH

3031

Igua

nodont

iaT

enonto

sauru

sti

llet

oru

mN

. M

acle

od

Low

er C

reta

ceous

Blu

ntB

lunt

-conc

ave

MC

Z 4

205

Igua

nodont

iaT

enonto

sauru

sti

llet

oru

mN

. M

acle

od

Low

er C

reta

ceous

Blu

ntB

lunt

-conv

ex

TM

MC

A C

UB

0.5

3Ig

uano

dont

iaT

enonto

sauru

sti

llet

oru

mN

. M

acle

od

Low

er C

reta

ceous

Poin

ted

Poin

ted-c

onv

ex

LL

.12275

Igua

nodont

iaT

enonto

sauru

sti

llet

oru

mT

enna

nt (

2010)

Low

er C

reta

ceous

Poin

ted

Poin

ted-c

onc

ave

YP

M 1

887

Igua

nodont

iaT

hei

ophyt

alia

ker

riA

. M

cDona

ldL

ow

er C

reta

ceous

Poin

ted

Poin

ted-c

onv

ex

R3398

Rha

bdodont

idae

Zalm

oxes

robust

us

Wei

sham

pel

et

al.

(2003)

Upper

Cre

tace

ous

Poin

ted

Poin

ted-c

onc

ave

A Geometric Morphometric Analysis of Ruminant (Ungulata: … · 2015-12-04 · 2 Figures and Tables [10] Figure 1 - Mean shape and range envelopes of browsing, grazing, and intermediate

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