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Re: Sauropod ancestry?
On Tue, 18 Jul 2000 Dinogeorge@aol.com wrote:
> In a message dated 7/18/00 1:25:05 PM EST, firstname.lastname@example.org writes:
> << I second the query about early sauropodomorphan pedal digits. I'm not
> entirely convinced that Prosauropoda is monophyletic, either (although a
> good chunk of Prosauropoda being monophyletic seems likely). >>
> The prosauropods that have their mandibular joint set well below the dentary
> tooth row almost certainly form a monophyletic group.
I would not be so sure. My current analysis finds extreme paraphyly of
the prosauropoda with some Jurassic forms, such as Massospondylus,
Lufengosaurus and Yunnanosaurus sharing a more recent common ancestor
with Sauropoda than with Plateosaurus (or at least the Trossingen and
Halberstadt creature we call Plateosaurus - it probably isn't). This is
actually based on a host of Cranial and Postcranial characters. As for
the digit thing, sauropod fifth digits have the same components as
derived prosauropods, namely one metatarsal and one phalanx (some
sauropods have a small extra nubbin-like terminal phalanx but it is hard
to see how this is a big deal). They differ only in a quantative manner
with sauropods having more robust elements (not suprising since the
digit was in contact with
the ground when the foot was not being lifted). However the fifth digit
may not have re-established contact with the ground through enlargement
of the fifth digit, but more by shortening of the other four digits.