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Re: for David M.: Scleromochlus ankles + Brusatte et al. supertree



> It's well known that the calcaneal 'heel' of basal crocodylomorphs is  
> rather small structure, amplified in certain derived quadrupedal  
> taxa. And that there have been a number of papers about bipedality in  
> basal crocodylomorphs.

All irrelevant; when the calcaneum can't move against the lower leg (which is 
the case when there's a mesotarsal joint), the shape of the calcaneum doesn't 
matter.

> If you look at either Sereno's 1991 figure 17  
> (calcaneum mislabeled 'dt4') or Benton's 1999 figure 13 (calcaneum  
> mislabeled 'astragalus') Scleromochlus has a minor calcaneal heel  
> [...]
>
> How else do you see it, David? I'd like to know to correct any  
> misconceptions I may have.

Hm. It is indeed interesting that these slightly shaded line drawings are not 
identical, and that Sereno identifies as dt4 and dt3 what Benton calls 
astragalus and calcaneum. (Sure, the bones are small, but not that small...) 
However, Benton's drawing of what he calls the astragalus does in fact look 
like an archosauromorph astragalus. Why do you think it's a calcaneum, and can 
you see the joint between as and ca anywhere?

> Benton 1985 found pterosaurs to nest between Trilophosaurus and
> Lepidosauromorpha rather than with Euparkeria and later archosaurs.

First of all, Benton did not find anything in 1985. That paper does not contain 
a data matrix, and there's not the slightest hint that Benton conducted a 
phylogenetic analysis of any kind in order to arrive at that tree. He simply 
presents a tree, and a list of characters that agrees with this tree. That's 
all. Was fashionable at that time (see Milner 1988 and 1993 on tetrapod 
phylogeny and the origin of lissamphibians, for example), but it's not science 
because the tree is not reproducible.

(I have heard a particularly evil rumor on what exactly Benton did to get that 
tree. But without access to any potential evidence I better shut up.)

Secondly, I bet that all characters and taxa that Benton's tree contains have 
also been used in at least some of the more recent analyses -- all of which 
(yours included) found different results.

> Peters 2000 found pterosaurs to nest with Longisquama, Sharovipteryx,
> Cosesaurus, and Langobardisaurus rather than any tested archosaur.

Yeah, but till yesterday you didn't even know how to make sure that a data 
matrix is even fit for phylogenetic analysis.

> Everyone has known for a long, long, time, pterosaurs don't quack
> like an archosaur.

That proves it then.

> It's also important to get characters scored right. We can all help
> each other in that regard.

Quite so. It's also important to make sure there are no correlated characters 
in the matrix, for example.

> Regarding questions of morphospace, I would caution: first get the
> phylogeny right with an ultracomprehensive cladistic analysis of the
> Amniota.

Why all of Amniota, when even you agree pterosaurs are crown-group diapsids?

(That said, just wait for my thesis, which will be about Amniota as a whole. No 
results so far.)

> Right now there are too many questions, too many bad
> nestings that don't make sense.

This is science here. It doesn't matter if something makes sense to our 
expectations. What matters is whether it's demonstrably wrong.

> To quote an esteemed expert on pterosaurs, Chris Bennett 1996 (and  
> also quoted by Hone and Benton 2007): "ââ few characters can be found 
> that unite [pterosaurs] with any other clade among the archosaurs.â
>
> To quote another esteemed expert on pterosaurs, David Unwin 2004, "  
> But there are difficulties with this suggestion [that Scleromochlus  
> is the closest known relative of pterosaurs] and with the more  
> general idea that pterosaurs are ornithodirans."

That does _not_ mean that any other hypothesis would have even more characters 
and even fewer difficulties.
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