[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Which is Cosesaurus?



-----Original Message-----
From: Ken Kinman <kinman@hotmail.com>
To: dinosaur@usc.edu <dinosaur@usc.edu>
Date: Monday, June 05, 2000 5:19 PM
Subject: Which is Cosesaurus?


>   Question: Is Cosesaurus a prolacertiform or an ornithodiran archosaur?
> Sereno (1991), who places pterosaurs in Ornithodira, does not even mention
>Cosesaurus, so I assume he regarded it as prolacertiform.  I am wondering
if
>Sereno (or any others who regard pterosaurs as ornithodirans) have
responded
>to the more recent theory that pterosaurs are prolacertiforms (Cosesaurus
>being an intermediate between earlier prolacertiforms and pterosaurs).
> Is there anything in Cosesaurus that would preclude it from being
>regarded as closer to ornithodirans than to prolacertiforms?  And if so,
>could all the similarities between pterosaurs and Cosesaurus be a bunch of
>convergences?


Interesting question. I proposed a similar one about a month ago reguarding
Dave Peter`s phylogeny placing such prolacertilians as Ornithodirans. I
argued that they did not posess a key ornithodiran character....the Advanced
Mesotarsal ankle joint. Chris Bennett responded with the following: " The
reason
that the David Peters puts the Prolacertiformes in the Ornithodira is that
Paul Sereno defined Ornithodira as all descendents of the common ancestor of
Pterosauria and Dinosauria... "....so,... Dave Peters is calling them
ornithodiran simply because he sees them as being ancestral to pterosaurs.
(although I don`t believe he sees them as ancestral to dinosaurs....is this
making things any clearer??????)

I suspect that Cosesaurus had a Croc-reversed ankle type. This could have
been a precursor to the AM condition. Also, some people don`t believe
Cosesaurus (or other prolacertilians) had true Antiorbital fenestrae. They
quote "poor fossil preservation" as making this identification difficult.

I personally think that even if prolacertilians didn`t have all the
characters to qualify them as ornithodiran per se, they still could have
been ancestral to the group.