Diversity of sauropod dinosaurs from the Wealden (Lower Cretaceous) Supergroup of southern England Michael P. Taylor Palaeobiology Research Group School of Earth and Environmental Sciences University of Portsmouth Portsmouth PO1 3QL <[email protected]>
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Diversity of sauropod dinosaurs from the Wealden (Lower Cretaceous) Supergroup of southern England Michael P. Taylor Palaeobiology Research Group School.
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Diversity of sauropod dinosaursfrom the Wealden (Lower Cretaceous)
Supergroup of southern England
Michael P. TaylorPalaeobiology Research Group
School of Earth and Environmental SciencesUniversity of Portsmouth
On average, 17 characters can be scored per taxon (5%)
This means their positions in the phylogeny are very unstable.
Is there really any point?
Is there really any point in analysing taxa this fragmentary?
Upchurch, Paul, Paul M. Barrett, Zhao Xijin And Xu Xing. 2007. Are-evaluation of Chinshakiangosaurus chunghoensis Ye vide Dong 1992(Dinosauria, Sauropodomorpha): implications for cranial evolution inbasal sauropod dinosaurs. Geological Magazine (preprint).doi:10.1017/S0016756806003062
This is based on an analysis of Chinshakiangosaurus, based on a singledentary, which can be scored for just 13 characters in the matrix of Galtonand Upchurch (2004).
Even fragmentary specimens have information to bring to the party.
Cladogram 1
New taxon X. added to theanalysis of Harris (2006).
50% majority rule.
(In press as we speak.)
Cladogram 1
New taxon X. added to theanalysis of Harris (2006).
50% majority rule.
(In press as we speak.)
Well Behaved
Cladogram 1
New taxon X. added to theanalysis of Harris (2006).
50% majority rule.
(In press as we speak.)
Looks
Well Behaved
Cladogram 2
All seven new taxaadded to the analysisof Harris (2006).
Strict consensus.
Cladogram 2
All seven new taxaadded to the analysisof Harris (2006).
Strict consensus.
Giant, uninformativeneosauropod polytomy.
Cladogram 3
All seven new taxaadded to the analysisof Harris (2006).
50% majority rule.
Less uninformative.Still pretty poor.
Cladogram 3
All seven new taxaadded to the analysisof Harris (2006).
50% majority rule.
Less uninformative.Still pretty poor.
Five of seven new taxaare unresolvedneosauropods.
Cladogram 3
All seven new taxaadded to the analysisof Harris (2006).
50% majority rule.
Less uninformative.Still pretty poor.
Five of seven new taxaare unresolvedneosauropods.
Note that Diplodocoideais broken up.
Cladogram 3
All seven new taxaadded to the analysisof Harris (2006).
50% majority rule.
Less uninformative.Still pretty poor.
Five of seven new taxaare unresolvedneosauropods.
Note that Diplodocoideais broken up.
The arrangement ofexisting taxa (those inHarris 2006) is alsoaffected.
Taxa from Harris (2006).New taxa omitteda priori.
Topology consistent withthat recovered by Harris.
- No “cetiosaurid” clade.- Jobaria is inside Neosauropoda.- Haplocanthosaurus is outside Neosauropoda!
Cladogram 4
Cladogram 5
Taxa from Harris (2006).New taxa omitteda posteriori.
(So new taxa influencecharacter states.)
- “Cetiosaurid” clade.- Jobaria moved outside Neosauropoda.- Haplocanthosaurus moved inside Neosauropoda!
Intermission
Intermission:Brachiosaurus brancai(reconstruction from Paul 2000)
“Supertree” of sevenseparate analyses.
(One for each new taxon.)
Cladogram 6
“Supertree” of sevenseparate analyses.
(One for each new taxon.)
Cladogram 6
Exciting!
“Supertree” of sevenseparate analyses.
(One for each new taxon.)
Cladogram 6
Exciting!
... but dishonest
Cladogram 7
“Supertree” of sevenmajority-rule trees madeby a posteriori deletion.
This is honest.
All character scores aretaken into account.
Cladogram 7
“Supertree” of sevenmajority-rule trees madeby a posteriori deletion.
This is honest.
All character scores aretaken into account.
Resolution is a little betterthan in Cladogram 3 dueto the separate use ofmajority-rule for eachtaxon's results.
Five new taxa moved frombasal Neosauropoda tobasal Diplodocoidea orbasal Macronaria.
All seven new taxaadded to the analysisof Harris (2006).
50% majority rule.
Cladogram 3Remember?
Cladogram 7
“Supertree” of sevenmajority-rule trees madeby a posteriori deletion.
Happy Ending!
The Moral
Arrrrgh!The Moral
Arrrrgh!
Is there nothing left to believe in?
It's not quite that bad.
“Pelorosaurus” becklesi comes out in the same place in every analysis,even under strict consensus.
It is a basal titanosaur, the sister to Malawisaurus – the only known English titanosaur.
Since it is not congeneric with Pelorosaurus, it needs a new name.
Now what?
The solution is to code for more characters.
I have a further 33 dorsal vertebra characters to add:
– 11 of the centrum– 12 of the neural arch– 10 of the neural spine
This should at least double the scoring density of each of the new taxa.
... and may also foul up existing relationships :–)
Conclusions
Nearly all Wealden sauropod specimens are extremely fragmentary.
Current Wealden sauropod taxonomy is an unholy mess.
All analysed specimens represent neosauropods.
Few can be identified below the level of either Diplodocoidea or Macronaria,and even these identifications are vulnerable.
“Pelorosaurus” becklesi is secure as a basal titanosaur.
Since “Pelorosaurus” becklesi is not Pelorosaurus, and since it is the only knownEnglish titanosaur, it needs a new name.
Many new characters of the dorsal vertebra will clarify the relationships of theother Wealden specimens.
Cladistic hypotheses are MUCH, MUCH, MUCH less secure then they letyou think.
Thanks for listening
Sandra D. Chapman allowed access to the NHM specimens.
Mathew J. Wedel provided much-needed encouragement.
Darren Naish provided historic literature and background information.
Discussion with Paul Upchurch greatly improved my understanding ofwhat I was doing with the cladistic analysis.
My wife gave me a lift to this conference.
Cladogram 8
“Supertree” of sevenmajority-rule trees madeby a posteriori deletionwith backbone constraint.
This is insane.
Cladogram 8
“Supertree” of sevenmajority-rule trees madeby a posteriori deletionwith backbone constraint.
This is insane.
Ignore this.
Cladogram 8
“Supertree” of sevenmajority-rule trees madeby a posteriori deletionwith backbone constraint.