Dockum critters (was Re: Protoavis?)

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 08:25 AM 10/20/97 -0400, Ronald I. Orenstein wrote:
>This is probably going to rank as Stupid Question of the Century, but:
>
>Chatterjee has described, not just Protoavis, but what he claimed to be a
>Triassic "ornithomimid" from, I think, the same area.  So we have two
>creatures from the Triassic (if correctly identified) that appear to be far
>too early to have the features they show.  So...
>
>Is there the remotest chance that they or the beds they come from are
>misdated, and are actually much later than the Triassic?  If they were,
>say, late Jurassic or early Cretaceous instead of Triassic, we could all
>breathe more easily, couldn't we?

The Dockum is very, very clearly Late Triassic.  The vast majority of
identifiable bits are typical Late Tr critters.  See these refs for details:

Murry, P.A.  1986.  Vertebrate paleontology of the Dockum Group, western
Texas and eastern New Mexico. pp. 109-137.  IN Padian, K. (ed.) The
Beginning of the Age of Dinosaurs: faunal change across the
Triassic-Jurassic boundary.  Cambridge Univ. Press.

Chatterjee, S.  1986.  The Late Triassic Dockum vertebraets: their
stratigraphic and paleobiogeographic significance.  pp. 139-150.  IN Padian,
K. (ed.) The Beginning of the Age of Dinosaurs: faunal change across the
Triassic-Jurassic boundary.  Cambridge Univ. Press.

Note that Chatterjee has claimed at times that he has found the oldest
member of the (or ancestor of the) tyrannosaurs (Postosuchus, now known to
be composed of two different taxa), ornithischians (Technosaurus), birds
(Protoavis), ornithomimosaurs (Shuvosaurus), and pterosaurs (a critter at
last SVP) in his quarry.  Chatterjee is known to be a supporter of Colbert's
view (that all the interesting evolution in the Mesozoic was over by the
Late Triassic, and that the Jurassic and Cretaceous was just about
"fine-tuning" the new groups).

Regardless of the affinities of these fossils, the quarry IS Late Triassic.
If these affiliations prove true, it will require reinterpretation of the
timing of these origins.  Nevertheless, I'll have to add in closing that
Chatterjee has very conventional views of the position of these groups
within their respective clades.  Much as Martin & Feduccia would like
otherwise, Chatterjee is pretty clearly convinced of the maniraptoran nature
of birds.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661