diversity of sauropod dinosaurs from the wealden (lower cretaceous) supergroup of southern england...

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

Portsmouth PO1 3QL<dino@miketaylor.org.uk>

Diversity of sauropod dinosaursfrom the Wealden (Lower Cretaceous)

Supergroup of southern England-- or --

Far too many virtually identicaland horribly unresolved cladograms

Michael P. TaylorPalaeobiology Research Group

School of Earth and Environmental SciencesUniversity of Portsmouth

Portsmouth PO1 3QL<dino@miketaylor.org.uk>

Diversity of sauropod dinosaursfrom the Wealden (Lower Cretaceous)

Supergroup of southern England-- or --

A cladistics horror-story

Michael P. TaylorPalaeobiology Research Group

School of Earth and Environmental SciencesUniversity of Portsmouth

Portsmouth PO1 3QL<dino@miketaylor.org.uk>

The Wealden Supergroup

Covers much of the south of Englandincluding the Isle of Wight.

Extends through much of theLower Cretaceous (Berriasian-Barremian).

Contains many historically importantdinosaur fossils:

– Iguanodon– Hypsilophodon– Baryonyx– Neovenator– Eotyrannus

But apart from these, most remains arefragmentary and difficult to interpret.

Sauropod specimens

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

New taxon “X.” BMNH R2095

“Ornithopsis” type specimen BMNH R28632

“Eucamerotus” type specimen BMNH R2522

“Eucamerotus” referred specimens R88/89

BMNH R88 and R89; I call it “UU” since I think of it as “Eueucamerotus”.

“Eucamerotus” referred specimen R90

“Eucamerotus” referred specimen R2523

“Pelorosaurus” becklesi BMNH 1868

The only specimen that is not a dorsal vertebra.

Humerus UlnaRadius

Scoring the new taxa

I added these taxa to the matrix of Harris (2006), which combinesthe scores of Wilson (2002) and Upchurch et al. (2004).

They can be scored for very few of the 331 characters.

Taxon #scores ProportionX 13 4%Ornithopsis 7 2%Eucamerotus 11 3%UU 31 9%R90 16 5%R2523 20 6%P. becklesi 18 5%

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.

This is insane.

Ignore this.

I mean it.