Biostratigraphic and palaeoclimatic meaning of the Middle Pleistocene South American rodent Ctenomys kraglievichi (Caviomorpha, Octodontidae)

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Palaeogeography, Palaeoclimatology, Pa

Biostratigraphic and palaeoclimatic meaning of the Middle

Pleistocene South American rodent Ctenomys kraglievichi

(Caviomorpha, Octodontidae)

Diego H. Verzia,*, Cecilia M. Deschampsb, Eduardo P. Tonnib

aDepartamento Cientifico Zoologıa Vertebrados, Museo de La Plata, Paseo del Bosque s/n 1900 La Plata, ArgentinabDepartamento Paleontologıa Vertebrados, Museo de La Plata, 1900 La Plata, Argentina

Received 14 January 2004; received in revised form 8 June 2004; accepted 8 June 2004

Abstract

The systematics and the geographic and stratigraphic distribution of a large and peculiar Pleistocene Ctenomys (Rodentia,

Octodontidae) of Argentina are revisited. Based on the geological range of this species, and paleomagnetic and

biochronological data of the bearing units, the stratigraphy and chronology of the Bonaerian Stage (Middle Pleistocene) is

refined and a new biozone is proposed for the Argentine pampean region. Morphological features of this species and its

association with other caviomorph taxa of Brazilian origin suggest that this rodent fauna represents an immigration event

triggered by an important warm climatic pulse. We suggest that this warm pulse, the most important so far recorded for southern

South America, may be correlated to the Middle Pleistocene OIS 11 recorded worldwide.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Rodentia; Octodontidae; Middle Pleistocene; Argentina; Stratigraphy; Palaeoclimate

1. Introduction

Several recent papers reflect efforts in learning

about the biostratigraphy and palaeoenvironments of

the pampean region in Argentina (e.g. Tonni and

Cione, 1999 and literature therein; Cione and Tonni,

0031-0182/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.palaeo.2004.06.010

* Corresponding author. Fax: +54 221 4257527.

E-mail addresses: [email protected]

(D.H. Verzi)8 [email protected] (C.M. Deschamps)8

[email protected] (E.P. Tonni).

2001). However, at least in the case of caviomorph

rodents, it is still necessary to intensify systematic

studies, prior to evaluating their significance as

potential tools in biostratigraphic and palaeoenviron-

mental studies based on micromammals. In many

cases the systematics of these rodents is clearly known

only to supraspecific levels. The main goal of this

paper is to contribute to the knowledge of these

subjects for the pampean region of Argentina through

the study of a caviomorph species of the Family

Octodontidae.

laeoecology 212 (2004) 315–329

D.H. Verzi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 212 (2004) 315–329316

Octodontidae of the Subfamily Ctenomyinae is

represented in the South American modern fauna by a

single genus, Ctenomys. It is the most polytypic genus

of subterranean rodents worldwide, including nearly

60 extant species commonly known as tuco-tucos

(Reig et al., 1990; Cook et al., 2000). Tuco-tucos are

currently distributed over a great area of South

America between 158S and 558S latitude (Reig et

al., 1965). They inhabit mostly loose and well-drained

soils, within a wide variety of habitats with diverse

vegetational characteristics (Reig et al., 1990). The

most ancient members of the genus have been

recorded in Pliocene sediments of central-eastern

(San Andres Formation, Upper Marplatan Stage;

Vucetich and Verzi, 1995) and northwestern Argen-

tina (Uquıa Formation; Walther et al., 1996, 1998).

For the Pleistocene, nearly 12 nominal species of

Ctenomys have been described for Argentina, Uru-

guay and Bolivia, but most of them have not been

revisited since their original description (Rusconi,

1931; Reig et al., 1990).

A large and peculiar Ctenomys has been found in

several Pleistocene localities along the Atlantic coast

of central Argentina and in Uruguay (Rusconi, 1930,

1931; Mones and Castiglioni, 1979). In Argentina, it

is associated with other caviomorph rodents that

represent an immigration event triggered by an

important warm climatic pulse previously reported

(Vucetich et al., 1997; Vucetich and Verzi, 2002). In

this paper we revisit the systematics, and the geo-

graphic and stratigraphic distribution of this Ctenomys

species. On this basis, a new biozone that allows

refinement of the Middle Pleistocene biostratigaphy of

the pampean region is proposed. A reassessment of

the biochronological and paleomagnetic data permits

the relative dating of this unit. The significance of the

climatic change represented in the new biozone is

discussed in light of other worldwide Pleistocene

climatic evidence.

2. Materials and methods

The material (including casts) of extinct and

living species of Ctenomys analyzed belong to the

collections of: Museo de La Plata, Argentina (MLP);

Museo Argentino de Ciencias Naturales bBernardinoRivadaviaQ, Buenos Aires, Argentina (MACN);

Paleontologıa Vertebrados Instituto Miguel Lillo,

Tucuman, Argentina (PVL); Museo de Ciencias

Naturales de Mar del Plata bL. ScagliaQ, Argentina(MMP); Catedra de Geologıa Historica, Universidad

Nacional del Sur, Argentina (UNSGH); Museo

Nacional de Historia Natural de La Paz, Bolivia;

Museo Nacional de Historia Natural de Montevideo,

Uruguay (MNHN-DP); Museum National d’Histoire

naturelle, Paris, France (MNHN PAM). Available

holotypes and referred materials of the extinct

species of Ctenomys (including Megactenomys and

Paractenomys; Rusconi, 1931; Mones, 1986; Verzi

and Lezcano, 1996) were revised. The holotypes of

Ctenomys latidens and C. bonariensis were studied

through casts. The holotypes of C. lujanensis, C.

subquadratus, C. brachyrhinus and C. subassen-

tiens, and a material referred to the latter were

studied through illustrations (Ameghino, 1889 pl. VI,

figs. 20–22; Ameghino, 1902 pl. IV, figs. 19–21;

Frailey et al., 1980, figs. 2 and 3). Skulls of the

following living species were used as comparative

material: C. australis, C. azarae, C. bonettoi, C.

bchasiquensisQ, C. dorbignyi, C. flamarioni, C.

frater, C. fulvus, C. haigi, C. leucodon, C. lewisi,

C. magellanicus, C. maulinus, C. mendocinus, C.

opimus, C. pearsoni, C. perrensi, C. porteousi, C.

robustus, C. roigi, C. sociabilis, C. steinbachi, C.

talarum and C. tuconax and illustrations of other

four species (C. boliviensis, C. conoveri, C. minutus,

and C. paraguayensis; Cook et al., 1990; Contreras,

2000). The following cranial, mandibular and dental

measurements were taken: BB, bulla breath; BIN,

breath of the incisive foramina; BLI, breath of lower

incisor; BR, breath of rostrum; BUI, breath of upper

incisor; DLI, depth of lower incisor; DM, mandib-

ular height below DP/4; DM/3, maximum diameter

of M/3; DUI, depth of upper incisor; IB, interorbital

breath; LAL, alveolar length of lower tooth row; LB,

length of bulla; LDP4, length of DP4; LDP/4, length

of DP/4; LIN, length from incisive foramen to the

alveolus of DP4; LLD, length of lower diastema;

LM1, anteroposterior length of M1; LM/1, anterola-

bial–posterolingual length of M/1; LM2, anteropos-

terior length of M2; LM/2, anterolabial–

posterolingual length of M/2; LM3, anteroposterior

length of M3; LP, length of palate; LUD, length of

upper diastema; PROC, procumbency of upper

incisor (Thomas’ angle; see Reig et al., 1965);

Fig. 1. Ventral (A–E), dorsal (F–G) and lateral (H–I) views of skulls of Ctenomys kraglievichi. (A) MACN 6457, holotype of bMegactenomysQkraglievichi; (B) MMP 429-M; (C) MACN 10846, holotype of Ctenomys dasseni longirostris; (D, G and I) MLP 92-VII-5-1; (E, F and H)

UNSGH 330. Scale=10 mm.

D.H. Verzi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 212 (2004) 315–329 317

D.H. Verzi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 212 (2004) 315–329318

UAL, alveolar length of upper tooth row; ZP, length

between the alveolus of the DP4 and the anterior

margin of the ventral zygomatic root; ZP/LDP4,

index between ZP and LDP4.

Measurements of Ctenomys kraglievichi and of the

extinct species considered as potential synonyms

(Appendix A) were log10 transformed and examined

through factor analysis (principal component extrac-

tion method, PCA) of the correlation matrix (Legen-

dre and Legendre, 1998).

3. Systematics

Order RODENTIA Bowdich, 1821

Infraorder CAVIOMORPHA Wood and Patterson in

Wood, 1955

Family OCTODONTIDAE Waterhouse, 1839

Subfamily CTENOMYINAE Tate, 1935

Genus Ctenomys de Blainville, 1826

Ctenomys kraglievichi (Rusconi, 1930) (Figs. 1 and 2;

Table 1)

Megactenomys kraglievichi Rusconi, 1930

Ctenomys dasseni longirostris Rusconi, 1931

Ctenomys praderii Mones and Castiglioni, 1979

Ctenomys kraglievichi Verzi and Lezcano, 1996

Holotype: MACN 6457 (holotype of Megactenomys

kraglievichi), damaged rostrum with both I1 and left

DP4.

Fig. 2. Lateral (A, C) and occlusal (B) views of mandibles of Ctenomys

Ctenomys dasseni longirostris. Scale=10 mm.

Hypodigm (see Appendix A for material details): the

holotype and MACN 10846 (holotype of Ctenomys

dasseni longirostris); MNHN-DP 533 (holotype of

Ctenomys praderii); MLP 52-X-1-6; MLP 91-IV-25-

97; MLP 91-IV-25-160; MLP 92-VII-5-1; MLP 92-

XI-12-1; MLP 03-II-15-1; MMP 366-S; MMP 429-

M; MMP 512-S; MMP 513-S; MMP 517-S; MMP

527-S; MMP 626-S; MMP 628-S; MMP 632-S;

MMP 684-S; MMP 689-S; MMP 1330-M; MMP

2350-M; MMP 2351-M; MMP 2353-M; UNSGH

330; UNSGH 321.

Emended diagnosis: large size, similar to that of the

largest living species C. conoveri. Descending dorsum

of the skull, especially the braincase. Wide rostrum.

Large interpremaxillary foramen and narrow incisor

foramina, with almost parallel margins. Ventral

zygomatic root wide, and strongly ahead relative to

the DP4. Cranial diastema strongly ascending ante-

riad. Zygomatic arches strongly bowed. Jugal with

dorsal suborbitary fossa. Small and narrow auditive

bullae. Mandible with dorsal portion of the masseteric

fossa deep; symphysal region procumbent and robust.

Masseteric crest subhorizontal. Incisors deeply

implanted and with the extra-alveolar portion very

long. I1 procumbent and subquadrangular in section;

its bottom lying on a lateral extension of the

maxillary, level with DP4-M1; enamelled side usually

with one or more longitudinal furrows, and with the

external margin forming a rounded and protruding

edge accompanied by a shallow depression of the

dentine. The bottom of the i1 forming a bulge on the

kraglievichi. (A, B) MMP 429-M; (C) MACN 10846, holotype of

Table 1

Cranial, mandibular and dental measurements (mm and degrees) of the holotypes and hypodigms of Ctenomys kraglievichi, Ctenomys dasseni, Ctenomys dasseni longirostris,

Ctenomys intermedius, Ctenomys latidens, Ctenomys magnus, Ctenomys praderii and Ctenomys sp.

Ctenomys kraglievichi Ctenomys

dasseni

longirostris

Ctenomys

praderii

Ctenomys

intermedius

Ctenomys

dasseni

Ctenomys

latidens

Ctenomys

magnus

Clenomys sp.

MACN 6457

holotype

n XFS.D. MACN 10846

holotype

MNHN-DP

533 holotype

MACN 1849

holotype

n XFS.D. PVL 739

holotype

MNHN PAM

279 holotype

MACN 5559

holotype

n XFS.D.

LUD 16.61 14 15.92F1.65 19.02 14.96 15.86 5 14.75F0.97 15.66 2 14.36F0.09

BIN 2.45 12 2.30F0.52 2.68 2.70 2.03 5 1.89F0.16 2 2.50F0.19

LIN 10.46 14 9.90F1.20 8.66 10.66 10.13 5 9.11F0.75 9.72 2 7.96F0.06

BR 12 14.13F1.47 14.08 14.64 11.99 5 11.88F0.34 1 12.55

ZP 2.49 11 2.46F0.35 2.74 3.30 1.51 5 1.43F0.21 2 1.89F0.54

ZP/LDP4 0.67 9 0.73F0.07 0.90 0.83 0.59 5 0.53F0.08 2 0.61F0.15

LP 8 27.78F2.94 24.05 5 23.52F1.48 24.46 2 24.97F0.16

IB 6 11.50F1.57 1 9.21

LB 1 17.08 15.65 16.12

BB 1 7.08 7.30 8.97

UAL 8 11.52F1.08 9.98 4 10.27F0.44 10.16 1 10.66

BUI 4.21 13 4.05F0.52 4.00 3.80 5 3.31F0.09 3.80 2 3.64F0.04

DUI 3.86 13 3.70F0.63 4.68 2.70 5 3.20F0.21 3.67 2 3.30F0.11

LDP4 3.71 12 3.33F0.29 3.04 4.00 2.58 5 2.71F0.08 2.76 2 3.08F0.11

LM1 13 2.96F0.31 3.04 2.90 2.31 5 2.54F0.14 2.58 2 2.80F0.06

LM2 11 2.65F0.23 2.56 2.14 5 2.21F0.11 2.22 2 2.57F0.06

LM3 7 1.54F0.21 1.42 3 1.36F0.05 1.42

DM 12 11.29F1.32 12.64 10.76 10.98 12.29

LLD 13 9.70F0.94 9.38 10.49 8.47 9.97

LAL 6 11.96F1.40

BLI 11 3.72F0.48 3.46 3.93 3.63 4.12

DLI 9 3.53F0.48 3.26 3.73 3.10 3.74

LDP/4 12 3.94F0.38 3.36 3.29 3.11 4.18

LM/1 12 3.80F0.35 3.67 3.29 3.11 4.18

LM/2 12 3.33F0.44 3.36 3.11 2.76 3.56

DM/3 7 1.43F0.11 1.53 1.33

PROC (8) 118 4 119F5.35 5 114.8F5.17 1 108

See abbreviations in Materials and methods.

D.H.Verzi

etal./Palaeogeography,Palaeoclim

atology,Palaeoeco

logy212(2004)315–329

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D.H. Verzi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 212 (2004) 315–329320

posterior wall of the retromolar pit. Cheek teeth

surrounded by cementum. M3 is proportionally large.

Comparative analysis: Ctenomys kraglievichi is pecu-

liar especially because of its large size and the

morphology of the skull and incisors. Rusconi (1930)

first included this species in a single genus Mega-

ctenomys on the basis of the characters preserved in a

damaged rostrum (MACN 6457) found at the south-

eastern coast of Buenos Aires Province, north of the

city of Mar del Plata (Fig. 3). Verzi and Lezcano (1996)

placed the species in the genusCtenomys and expanded

the description on the basis of a better-preserved

material (MLP 92-VII-5-1) found in the coastal cliffs

of Necochea area, near Costa Bonita (Fig. 3).

The comparative analysis of unpublished and new

materials with extinct and living species shows that

Ctenomys kraglievichi has strong similarities with

other Pleistocene species of the southeastern Buenos

Aires Province, Argentina, and of Uruguay (Verzi and

Lezcano, 1996): Ctenomys dasseni Rusconi, Cten-

omys dasseni longirostris Rusconi, Ctenomys inter-

Fig. 3. Map showing the localit

medius Rusconi, Ctenomys latidens Gervais and

Ameghino, Ctenomys magnus Rusconi, Ctenomys

praderii Mones and Castiglioni, and Ctenomys sp.

from Miramar (for material data and geographic

distribution see Appendix A and Fig. 3).

All these materials share a medium to large size,

and procumbent incisors with a long extra-alveolar

portion. However, a PCA performed with the varia-

bles preserved in the type of Ctenomys kraglievichi

showed that the materials assigned to this species

from Northern Mar del Plata, Necochea area, and Bajo

San Jose separate from those of Ctenomys intermedius

(Rusconi, 1931) in the first component because of the

greater LUD, BUI, LDP4, ZP and ZP/LDP4 (Fig. 4,

Tables 1 and 2). Materials from Miramar occupy an

intermediate position. Since the factor loadings of the

mentioned variables are equal in sign (Table 2), it may

be assumed that the PC-1 represents size. Moreover, a

recent analysis (Mora et al., 2003) shows that the

mentioned characters of the diastema and incisors

display positive allometry in the genus. On the

ies mentioned in the text.

Fig. 4. Scatter plot of scores on PC1 and PC2 axes from a PCA of skull and dental variables of Ctenomys kraglievichi, Ctenomys intermedius,

and Ctenomys sp. from Miramar. Included specimens are shown in Appendix A.

D.H. Verzi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 212 (2004) 315–329 321

contrary, a revision of the morphology of living and

extinct Ctenomyinae suggests that the position of the

ventral zygomatic root with respect to DP4 (ZP and

ZP/LDP4) would not rely on size; the zygomatic root

is level with the DP4 in the large Pliocene ctenomyine

Actenomys (Verzi, 2002, Table 3).

No clear separation of samples was shown by the

second component of the PCA (Fig. 4, Table 2).

The type specimens of Ctenomys intermedius

(MACN 1849) and Ctenomys dasseni (PVL 739)

from the bEnsenadan stageQ of Olivos (Appendix A;

Rusconi, 1931) were not included in the PCA because

Table 2

Skull and dental variables loading pattern on the two first axes of

the PCA; eigenvalue and percent of total variance explained

Variable PC 1 PC 2

LUD 0.766* 0.200

BIN 0.532 �0.742*

LIN 0.400 0.819*

BUI 0.909* 0.094

DUI 0.691 �0.270

LDP4 0.869* 0.030

ZP 0.934* 0.003

ZP/LDP4 0.834* �0.015

Eigenvalue 4.656 1.344

Total variance (%) 58 17

Loads higher than 0.7 are indicated by an asterisk. See abbreviations

in Materials and methods.

they lack some of the characters comparable to those

of the type of Ctenomys kraglievichi. However, both

materials show an important character that supports

the results provided by the PCA: the dorsum of the

skull (only preserved in these types and MACN 5410)

is straight in lateral view, while it is strongly curved in

the specimens MLP 92-VII-5-1 from Costa Bonita

(Necochea area) and UNSGH 330 from Bajo San

Jose, assigned to C. kraglievichi, especially the

braincase preserved in the latter (Fig. 1H).

The species Ctenomys latidens from the bToscasdel Rıo de la PlataQ (but see Appendix A) and

Ctenomys magnus from the bBonaerian stageQ of

Tandil (Rusconi, 1931: 226), each one known by a

single mandibular fragment (Appendix A), also show

similarities with the materials assigned to Ctenomys

kraglievichi. A PCA performed with mandibular

measurements provided no clear discrimination

between the examined nominal species (Appendix

A). The mandibles of the Ctenomys species have few

diagnostic features. One of them is the morphology of

the masseteric crest, a character that shows some

interspecific variation in living and extinct represen-

tatives. In this sample, the crest of C. kraglievichi

rises more anteriorly and sub-horizontally, while in

Ctenomys latidens and Ctenomys dasseni this crest is

somewhat more posterior and descending. These

characters are not preserved in C. magnus.

D.H. Verzi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 212 (2004) 315–329322

We consider that the materials found in an area of

approximately 20 km between the northern border of

the city of Mar del Plata and Santa Clara del Mar

(named here Northern Mar del Plata), Necochea and

Bajo San Jose can be assigned to Ctenomys kraglie-

vichi (Fig. 3), including as junior synonyms Ctenomys

dasseni longirostris and Ctenomys praderii. On the

other hand, despite their similarities, according to our

results we suggest that the names Ctenomys dasseni,

Ctenomys intermedius, Ctenomys latidens and Cten-

omys magnus, be maintained.

4. Geological setting

The type specimens of Ctenomys kraglievichi and

Ctenomys dasseni longirostris were found in the cliffs

of Northern Mar del Plata (Fig. 3), but both lack of

Fig. 5. Stratigraphic profiles of the localities bearing Cten

precise stratigraphic data (Rusconi, 1930, 1931). The

type and single specimen of Ctenomys praderii was

found in the Libertad Formation, outcropping at

Conchillas (Colonia Department, Uruguay; Fig. 3).

The fossil bearing unit was originally attributed to the

Pleistocene (Mones and Castiglioni, 1979). Later,

Marshall et al. (1984) cited this formation as

Ensenadan in age, older than the Lujanian Sopas

Formation. Recently Ubilla and Perea (1999) reas-

serted that b. . .many fossils assigned to the Libertad

Formation have usually unclear or wrong stratigraphic

provenance. . .QMost specimens of ancient collections have no

detailed stratigraphic data. However, new collections

made by the authors during the last decade in the

pampean region of Argentina yielded several remains

of Ctenomys kraglievichi with good stratigraphic

control (Appendix A, Fig. 5).

omys kraglievichi showing the C. kraglievichi zone.

D.H. Verzi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 212 (2004) 315–329 323

4.1. Northern Mar del Plata

Outcropping sequences of this area have been

described by Bidegain et al. (1998), Verzi et al.

(2002) and Cione et al. (2002). These sequences, 6

to 10 m thick, are composed of silty sands with

several interbedded calcrete crusts, paleosoils, and

conglomerate lenses. Ctenomys kraglievichi was

found in sandy to silty–sandy levels (Fig. 5) that

may be correlated to the middle levels of Bidegain et

al. (1998: 238, fig. 2, bU2Q–bU3Q), and the top of

bUnit 2Q and base of bUnit 3Q from Verzi et al.

(2002, fig. 6).

4.2. Necochea area

A description of the sequences cropping out at this

locality may be found in Tonni et al. (1996, fig. 2) and

Vucetich et al. (1997, fig. 2). The sequence, 4–6 m

thick, is composed predominantly of yellowish-brown

sandy silts with calcium carbonate bdollsQ and veins,

and channelled deposits which form diamictites with

large calcium carbonate clasts and blocks in a matrix

of sandy silts. At Las Grutas–Punta Negra the

specimens of Ctenomys kraglievichi were found in

lower part of level C (Vucetich et al., 1997). At Costa

Bonita, this species was found in brownish levels of

silty sands and clays belonging to the top of B, and C

(Fig. 5).

4.3. Bajo San Jose

The Bajo San Jose sequence was described in

detail by Borromei (1990) and Deschamps and

Borromei (1992). The whole profile, approximately

7 m thick, is composed of conglomerates, sands and

silts deposited by a gravel-braided river. Ctenomys

kraglievichi was found in a medium sand lens of the

Lower Section of the San Jose Sequence (Fig. 5).

5. Biostratigraphy and biochronology

The populational dynamic of Ctenomys includes

patchy distribution, together with frequent migration

and extinction events often dependent on climatic

cycles (Reig et al., 1990; Lessa, 2000). There are no

studies linking this dynamic with the characteristics

of the fossil record of the genus. But, the available

fossil data suggest that the species of Ctenomys

would have biochrons of short duration. Most of the

species recorded in the Quaternary are extinct

(Rusconi, 1931; Cione et al., 1999); and the biochrons

of the living species with known fossil record do not

extend below the Pleistocene–Holocene boundary

(e.g 10375F90 for C. talarum, Quintana, 2001;

8990F55 14 C years BP for Ctenomys cf. talarum

and Ctenomys cf. australis, Pardinas, 2001). In this

context, the levels bearing Ctenomys kraglievichi

would be confidently synchronous from a biostrati-

graphic point of view.

The Ctenomys kraglievichi Range Zone is defined

by the total range of the rodent C. kraglievichi,

associated with Hippidion principale (Perissodactyla,

Equidae), Megatherium americanum (Xenarthra,

Megatheriidae), Glyptodon clavipes, Panochthus

tuberculatus (Xenarthra, Glyptodontidae), and a

species still undescribed of Tolypeutes (Scillato-

Yane, pers. com.; Xenarthra, Dasypodidae). The

type area is Bajo San Jose, and the stratotype is a

sandy lens up to 1 m thick of the Lower Section of

the San Jose Sequence, 2 m from the base of the

profile (Fig. 5).

This biozone is also recognized at Costa Bonita

(top of Unit B and Unit C, 2 m thick) and Las Grutas–

Punta Negra (lower part of Unit C, up to 1.4 m thick)

in Necochea area, and at Camet (middle levels;

indeterminate thickness), and Constitucion (a level

at 3 m from the base of the profile, approximately 1 m

thick) in Northern Mar del Plata (Fig. 5).

The Ctenomys kraglievichi Range Zone correlates

chronostratigraphically with part of the Bonaerian

Stage, which Cione and Tonni (1999) based on the

Megatherium americanum Zone. The C. kraglievichi

Zone is temporally more restricted than that proposed

by these authors, and may be referred to the base of

the Bonaerian Stage (Fig. 6).

No absolute dating is known so far for the bearing

levels of Ctenomys kraglievichi. At Bajo San Jose the

bearing levels are referable to the Bonaerian. This

assignment was based on the finding of the exclusive

Bonaerian species Tolypeutes n. sp. (Scillato Yane,

pers. com.) and Hippidion principale, associated with

Megatherium americanum, Glyptodon clavipes and

Panochthus tuberculatus whose biochron encompass

the Bonaerian–Lujanian.

Fig. 6. Stratigraphic chart with a correlation to global climatic change. Stratigraphy modified from Cione and Tonni (1999); isotopic curve after

Shackleton (1995); the Plio-Pleistocene boundary follows Berggren et al. (1995).

D.H. Verzi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 212 (2004) 315–329324

Vucetich et al. (1997) discussed the biochronology

of Northern Mar del Plata and Punta Negra in

Necochea (see also Tonni et al., 1996). These authors

assigned tentatively the basal levels of Northern Mar

del Plata and level C of Punta Negra to the Ensenadan

(Mesotherium cristatum Zone, Soibelzon et al., in

press=Tolypeutes pampaeus Zone, Cione and Tonni,

1999).

Bidegain et al. (1998) studied the magnetostratig-

raphy of Northern Mar del Plata. They described two

zones of different magnetic polarity: the lower one

with reverse polarity, correlated to Matuyama Chron

(N0.78 Ma; Chron C1r1r after Berggren et al., 1995),

and the middle–upper one with normal polarity,

correlated to Brunhes Chron (b0.78 Ma; C1n after

Berggren et al., 1995) (Fig. 5). The boundary between

both paleomagnetic zones was detected between

bUnits 4 and 5Q (bU4Q–bU5Q after Bidegain et al.,

1998; Fig. 5). Ctenomys kraglievichi is recorded at

least 2.2 m above the magnetostratigraphic boundary,

hence, it will be younger than 0.78 Ma, reinforcing the

hypothesis of a Bonaerian age for the sediments

bearing this species.

6. Palaeoclimatic significance

The only exposures that have a known rich fossil

record of micromammals in levels bearing Ctenomys

kraglievichi and older ones are those of Necochea

area. This fact permits the analysis of the significance

of the presence of C. kraglievichi in a single

sequence. The basal levels of Las Grutas–Punta Negra

and Costa Bonita yielded numerous remains of the

older ctenomyines Eucelophorus chapalmalensis

(Reig and Quintana, 1992) and Ctenomys aff.

chapalmalensis (Tonni et al., 1996). The sudden

appearance of C. kraglievichi in both sequences is

accompanied by the extinction of these ctenomyines.

Two peculiar species of caviomorph rodents are

also suddenly recorded together with Ctenomys

kraglievichi: an Echimyidae closely related to the

living Clyomys (reported as Clyomys in Vucetich et

al., 1997) and the Dasyproctidae Plesiaguti totoi

(Vucetich and Verzi, 2002). The former was found

together with C. kraglievichi in unit C of Punta Negra,

Necochea, and in Santa Clara del Mar (Fig. 5;

Vucetich et al., 1997). This is the single record of a

D.H. Verzi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 212 (2004) 315–329 325

post-Pliocene echimyid at this latitude, whereas

Plesiaguti is the single dasyproctid recorded in the

Pleistocene of Argentina. Both species and C.

kraglievichi are clearly immigrants to the southern–

southeastern Buenos Aires province. The Brazilian

affinities (sensu Hershkovitz, 1958) of aff. Clyomys

and Plesiaguti, and the morphology of their rooted

molars suggest that they are associated with an

important warm pulse occurred within the lapse

represented in the C. kraglievichi Zone (Vucetich et

al., 1997; Vucetich and Verzi, 1999, 2002).

Ctenomys kraglievichi shows strong similarities

with chacoan species of Ctenomys from Bolivia and

Paraguay, characterized by a wide rostrum, strong

incisors, bowed zygomatic arches and narrow bullae

as in the recent C. conoveri and C. boliviensis (see

Anderson et al., 1987, fig. 7), and the extinct C.

subassentiens from the Pleistocene of Tarija, Bolivia

(see Frailey et al., 1980, fig. 2). The record of C.

kraglievichi represents the irruption of a Ctenomys

species with such affinities into the pampean region,

where at present predominate the species of the

mendocinus group (Massarini et al., 1991), a lineage

closely related to the Monte semiarid biome (see

Mares et al., 1985) from western Argentina.

The caviomorph species recorded in the Ctenomys

kraglievichi Zone suggest warmer environments,

although not clearly more humid than those present

ones at this latitude. The morphology of the base of

the I1 of aff. Clyomys, forming a conspicuous

prominence antero-external to the DP4 (Vucetich et

al., 1997), indicates a deep implantation of the I1

characteristic of octodontoids with fossorial to sub-

terranean habits. This morphology is shared with

Clyomys, which today inhabits savannahs and mar-

gins of dry forests, strongly seasonal environments, of

the Brazilian Cerrado and east of Paraguay (Eisenberg

and Redford, 1999; Mares et al., 1989).

Geological evidences of the biozone type area

suggest for the San Jose Sequence a stage of initial

filling of the valley in the transport zone, coeval with

a maximum sea level rise within an interglacial event

(Zavala and Quattrocchio, 2001). As well, in Santa

Clara del Mar (Northern Mar del Plata), Cione et al.

(2002, fig. 1) described a marine level that represents

the Belgranan ingression, which is recognized in the

Buenos Aires province from north to southeast as the

strongest sea level rise during the Pleistocene. This

marine unit overlies the Ensenadan, at the base of the

Bonaerian, and is paleomagnetically normal

(Brunhes); consequently it is younger than 0.78

Ma. The remains of aff. Clyomys from Santa Clara

del Mar described by Vucetich et al. (1997) were

found in levels immediately overlying the Belgranan

ingression.

Thus, the set of faunistic and geological evidences

suggest for the Ctenomys kraglievichi Zone an

important warm and probably dry (although seasonal)

episode, with rise of the sea level, corresponding to an

interglacial period.

As stated above, the caviomorph record in the

Ctenomys kraglievichi Zone is episodic because of the

previous extinction of taxa and the sudden appearance

of others. Clearly, these latter are members of an

immigration event into the southeastern Buenos Aires

Province related to the strongest warm pulse so far

recognized for the Pleistocene of southern South

America. Evidence in other continents suggests as

well an important warm pulse for the Middle

Pleistocene between 0.7 and 0.3 Ma (Vrba, 1985).

According to the biochronological and paleomagnetic

evidence, the climatic change identified in the C.

kraglievichi Zone may correspond to the OIS 11 or

13–15 after Shackleton (1995), recorded about 0.4

and the interval 0.5–0.6 Ma, respectively (Fig. 6).

Since the OIS 11 is remarkable worldwide as the

longest and warmest interglacial documented for the

past 0.5 Ma according to the sea level rise and

changes of faunal and vegetation composition (Kin-

dler and Hearty, 1995; Droxler et al., 1996; Tzedakis

et al., 1997), we suggest the warm pulse recorded may

be correlated with this Stage 0.4 Ma old.

Acknowledgements

We thank A.I. Olivares for assistance with data and

tables. J.F. Bonaparte, A.G. Kramarz, J. Powell, D.

Romero, A. Mones, R. Pascual, and M. Reguero, for

the access to materials under their care. We are

specially indebted with O.A. Scaglia, A. Dondas and

M. Castillo for their help with the materials and field

works. L. Ginsburg for providing the cast of the

holotype of Ctenomys latidens. The authors gratefully

acknowledge the thorough reviews by J.-L. Harten-

berger and M. Woodburne. This paper was partially

D.H. Verzi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 212 (2004) 315–329326

founded by CONICET PIP 2099, Universidad Nacio-

nal de La Plata Grants 11/N351 and 11/N335,

ANPCyT, and CIC-PBA.

Appendix A

Material of Ctenomys kraglievichi and similar

species analyzed. Specimens marked by an asterisk

were included in the PCA analysis.

A.1. Ctenomys kraglievichi

*MACN 6457 (holotype of Megactenomys kra-

glievichi), damaged rostrum with both I1 and left

DP4; North of Mar del Plata cliffs, Atlantic coast,

dubious horizon (see Verzi and Lezcano, 1996).

*MACN 10846 (holotype of Ctenomys dasseni

longirostris), damaged skull with right DP4-M2,

and left I1 and DP4-M2; both damaged mandibles

with DP/4-M/3; Mar del Plata, north of Arroyo

Camet (in schedis; Northern Mar del Plata).

*MNHN-DP 533 (holotype of Ctenomys praderii),

anterior portion of the skull with damaged right I1,

and both damaged DP4-M1; Libertad Formation,

Conchillas, Colonia Department, Uruguay. MLP 52-

X-1-6, left mandible with damaged I/1 and DP/4-M/

2; bPrebelgranenseQ of Frenguelli (in schedis, bio-

stratigraphically corresponding to the Bonaerian

Stage). *MLP 91-IV-25-97, anterior portion of the

skull with fragmented right I1, and both DP4-M2;

Costa Bonita top of level B (Necochea). MLP 91-IV-

25-160, left mandible with DP/4-M/3; Las Grutas

lower part of level C (Necochea). *MLP 92-VII-5-1,

anterior portion of the skull with both I1, right DP4-

M2 and left DP4-M3; near Costa Bonita level C

(Necochea). *MLP 92-XI-12-1, anterior portion of

the skull with complete dentition; Camet (Northern

Mar del Plata) middle levels. MLP 03-II-15-1,

anterior portion of the skull with left I1 and right

M1; Constitucion (Northern Mar del Plata), 3 m

from the base. MMP 366-S, both damaged man-

dibles, with both I/1, right DP/4-M/3 and left DP/4-

M/2; Playa Santa Elena (near Santa Clara del Mar,

Northern Mar del Plata). *MMP 429-M, anterior

portion of the skull with both I1, right DP4-M2 and

left DP4-M1; both mandibles with both I/1, right

DP/4-M/3 and left DP/4-M/2; Arroyo Santa Elena

(near Santa Clara del Mar, Northern Mar del Plata).

MMP 512-S, anterior portion of the skull with right

I1 and DP4-M2, and left DP4-M3; both damaged

mandibles with both I/1, right DP/4-M/2 and left DP/

4-M/3; Santa Elena (near Santa Clara del Mar,

Northern Mar del Plata). MMP 513-S, left mandible

with fragment of I/1 and DP/4-M/2; Santa Elena.

MMP 517-S, right mandible with fragment of I/1

and without molars; Santa Elena. MMP 527-S,

anterior portion of the skull with both I1 and left

DP4-M3; Santa Elena. MMP 626-S, anterior portion

of the skull with both I1, right DP4-M3 and left

DP4-M2; left mandible with I/1 and DP/4-M/3;

Santa Elena. MMP 628-S, anterior portion of the

skull with both I1, right DP4-M2 and left DP4-M1;

anterior part of the mandible with both I/1, right DP/

4-M/2 and left DP/4-M/1; Santa Elena. MMP 632-S,

anterior portion of the skull with both I1, right DP4-

M2 and left M1-2; Constitucion (Northern Mar del

Plata). MMP 684-S, both damaged mandibles with

both I/1 and DP/4-M/2; Santa Elena. MMP 689-S,

left mandible with I/1 and DP/4-M/2; between Camet

and Santa Clara del Mar (Northern Mar del Plata).

*MMP 1330-M, anterior portion of the skull with

both I1 and DP4-M3 (right I1 broken); Santa Elena.

MMP 2350-M, right mandible with I/1 and DP/4-M/

3; Constitucion, middle level. MMP 2351-M, ante-

rior portion of the skull with both I1, right DP4-M2

and left DP4-M1; Constitucion, middle level. MMP

2353-M, right mandible with I/1 and DP/4-M/3;

Constitucion, middle level. *UNSGH 330, skull with

right I1, fragmented left I1, left DP4-M1 and right

DP4-M2; Bajo San Jose, lower section of San Jose

Sequence. UNSGH 321, anterior portion of the skull

without dentition; Bajo San Jose, lower Section of

San Jose Sequence.

A.2. Ctenomys dasseni

PVL 739 (holotype, formerly Rusconi collection

161), damaged skull with right I1 and both DP4-M3;

right mandible with M/1-3 and left mandible with I/1

and DP/4-M/3; Olivos.

A.3. Ctenomys intermedius

MACN 1849 (holotype), skull with both DP4-M3;

Olivos. *MACN 1848, anterior portion of the skull

D.H. Verzi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 212 (2004) 315–329 327

with both I1, left DP4-M3 and right DP4-M2; Olivos.

*MACN 1850, anterior portion of the skull with both

I1, left DP4-M3 and right DP4-M2; Olivos. *MACN

5410, damaged skull with left I1 and DP4-M3, and

right DP4-M2; Alvear, Buenos Aires province (in

litt.). *MACN 6498, anterior portion of the skull with

both I1, left DP4-M3 and right DP4-M2; Olivos.

*MLP 54-III-5-2, anterior portion of the skull with

both I1, right DP4-M2 and left DP4-M1; between

Olivos and Punta Anchorena.

A.4. Ctenomys latidens

MLP 93-XII-15-1, cast of the holotype MNHN

PAM 279, right mandible with I/1 and DP/4-M/2;

dubious provenance (see Mones, 1994).

A.5. Ctenomys magnus

MACN 5559 (holotype), right mandible with I/1

and DP/4-M/2; Tandil, Buenos Aires province.

A.6. Ctenomys sp.

*MLP 91-IV-30-35, anterior portion of the skull

with both I1 and DP4-M2; Baliza Punta Hermengo,

Miramar, middle of level 5 (in schedis; level D in

Tonni et al., 1996). *MLP 91-IV-30-36, anterior

portion of the skull with both I1 and DP4-M2; Baliza

Punta Hermengo, Miramar, base of level 5 (in schedis;

level D in Tonni et al., 1996).

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