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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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Presentation on theme: "Diversity of sauropod dinosaurs from the Wealden (Lower Cretaceous) Supergroup of southern England Michael P. Taylor Palaeobiology Research Group School."— Presentation transcript:

1 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

2 Diversity of sauropod dinosaurs from the Wealden (Lower Cretaceous) Supergroup of southern England -- or -- Far too many virtually identical and horribly unresolved cladograms Michael P. Taylor Palaeobiology Research Group School of Earth and Environmental Sciences University of Portsmouth Portsmouth PO1 3QL

3 Diversity of sauropod dinosaurs from the Wealden (Lower Cretaceous) Supergroup of southern England -- or -- A cladistics horror-story Michael P. Taylor Palaeobiology Research Group School of Earth and Environmental Sciences University of Portsmouth Portsmouth PO1 3QL

4 The Wealden Supergroup Covers much of the south of England including the Isle of Wight. Extends through much of the Lower Cretaceous (Berriasian-Barremian). Contains many historically important dinosaur fossils: – Iguanodon – Hypsilophodon – Baryonyx – Neovenator – Eotyrannus But apart from these, most remains are fragmentary and difficult to interpret.

5 Sauropod specimens Mostly fragmentary (and that's being kind). But I want to figure out what they are.

6 New taxon X. BMNH R2095

7 Ornithopsis type specimen BMNH R28632

8 Eucamerotus type specimen BMNH R2522

9 Eucamerotus referred specimens R88/89 BMNH R88 and R89; I call it UU since I think of it as Eueucamerotus.

10 Eucamerotus referred specimen R90

11 Eucamerotus referred specimen R2523

12 Pelorosaurus becklesi BMNH 1868 The only specimen that is not a dorsal vertebra. HumerusUlna Radius

13 Scoring the new taxa I added these taxa to the matrix of Harris (2006), which combines the scores of Wilson (2002) and Upchurch et al. (2004). They can be scored for very few of the 331 characters. Taxon#scoresProportion X134% Ornithopsis72% Eucamerotus113% UU319% R90165% R % P. becklesi185% On average, 17 characters can be scored per taxon (5%) This means their positions in the phylogeny are very unstable.

14 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 A re-evaluation of Chinshakiangosaurus chunghoensis Ye vide Dong 1992 (Dinosauria, Sauropodomorpha): implications for cranial evolution in basal sauropod dinosaurs. Geological Magazine (preprint). doi: /S This is based on an analysis of Chinshakiangosaurus, based on a single dentary, which can be scored for just 13 characters in the matrix of Galton and Upchurch (2004). Even fragmentary specimens have information to bring to the party.

15 Cladogram 1 New taxon X. added to the analysis of Harris (2006). 50% majority rule. (In press as we speak.)

16 Cladogram 1 New taxon X. added to the analysis of Harris (2006). 50% majority rule. (In press as we speak.) Well Behaved

17 Cladogram 1 New taxon X. added to the analysis of Harris (2006). 50% majority rule. (In press as we speak.) Looks Well Behaved

18 Cladogram 2 All seven new taxa added to the analysis of Harris (2006). Strict consensus.

19 Cladogram 2 All seven new taxa added to the analysis of Harris (2006). Strict consensus. Giant, uninformative neosauropod polytomy.

20 Cladogram 3 All seven new taxa added to the analysis of Harris (2006). 50% majority rule. Less uninformative. Still pretty poor.

21 Cladogram 3 All seven new taxa added to the analysis of Harris (2006). 50% majority rule. Less uninformative. Still pretty poor. Five of seven new taxa are unresolved neosauropods.

22 Cladogram 3 All seven new taxa added to the analysis of Harris (2006). 50% majority rule. Less uninformative. Still pretty poor. Five of seven new taxa are unresolved neosauropods. Note that Diplodocoidea is broken up.

23 Cladogram 3 All seven new taxa added to the analysis of Harris (2006). 50% majority rule. Less uninformative. Still pretty poor. Five of seven new taxa are unresolved neosauropods. Note that Diplodocoidea is broken up. The arrangement of existing taxa (those in Harris 2006) is also affected.

24 Taxa from Harris (2006). New taxa omitted a priori. Topology consistent with that recovered by Harris. - No cetiosaurid clade. - Jobaria is inside Neosauropoda. - Haplocanthosaurus is outside Neosauropoda! Cladogram 4

25 Cladogram 5 Taxa from Harris (2006). New taxa omitted a posteriori. (So new taxa influence character states.) - Cetiosaurid clade. - Jobaria moved outside Neosauropoda. - Haplocanthosaurus moved inside Neosauropoda!

26 Intermission

27 Intermission: Brachiosaurus brancai (reconstruction from Paul 2000)

28 Supertree of seven separate analyses. (One for each new taxon.) Cladogram 6

29 Supertree of seven separate analyses. (One for each new taxon.) Cladogram 6 Exciting!

30 Supertree of seven separate analyses. (One for each new taxon.) Cladogram 6 Exciting!... but dishonest

31 Cladogram 7 Supertree of seven majority-rule trees made by a posteriori deletion. This is honest. All character scores are taken into account.

32 Cladogram 7 Supertree of seven majority-rule trees made by a posteriori deletion. This is honest. All character scores are taken into account. Resolution is a little better than in Cladogram 3 due to the separate use of majority-rule for each taxon's results. Five new taxa moved from basal Neosauropoda to basal Diplodocoidea or basal Macronaria.

33 All seven new taxa added to the analysis of Harris (2006). 50% majority rule. Cladogram 3 Remember?

34 Cladogram 7 Supertree of seven majority-rule trees made by a posteriori deletion. Happy Ending!

35 The Moral

36 Arrrrgh! The Moral Arrrrgh!

37 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.

38 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 :–)

39 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 known English titanosaur, it needs a new name. Many new characters of the dorsal vertebra will clarify the relationships of the other Wealden specimens. Cladistic hypotheses are MUCH, MUCH, MUCH less secure then they let you think.

40 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 of what I was doing with the cladistic analysis. My wife gave me a lift to this conference.

41 Cladogram 8 Supertree of seven majority-rule trees made by a posteriori deletion with backbone constraint. This is insane.

42 Cladogram 8 Supertree of seven majority-rule trees made by a posteriori deletion with backbone constraint. This is insane. Ignore this.

43 Cladogram 8 Supertree of seven majority-rule trees made by a posteriori deletion with backbone constraint. This is insane. Ignore this. I mean it.


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