Re: Sauropod Ancestors

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>I am extremely skeptical of the claim that the prosauropods do
>not include the ancestors of the sauropods.  There is a tendency
>for cladistic analysis to treat ancestors as a sister group, at
>least so it seems to me.

Concerning sauropod ancestors:

The recent claims that Prosauropoda is the sister-group, rather than a
paraphyletic stem group, of the Sauropoda basically hinges on a single
character, the fact that the fifth metatarsal of the foot is much more
reduced in prosauropods than in sauropods.  However, reversals happen (and
in fact, this particular reversal happens independantly in the origin of
the therizinosauroids), and one character taxa should always be held with
some reservation.

To my knowledge, no one has published an analysis (including data matrix)
for all sauropodomorphs [grad students looking for a major project, take
note!].  I suspect that, when one is run, the sauropods will fall among the
"melanorosaurids" sensu lato.

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist                           Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.