Incidentally, even if there were a mid-sized tyrannosaurid in the Hell Creek,
it doesn't make a difference to the
>> big pattern
we were describing: namely, the extreme taxonomic diversity and even size
distribution in the Morrison
>> versus the more
restricted taxonomic diversity and very uneven size distribution (all big
carnivores being tyrannosaurids)
>> in the Hell Creek,
Judith River, and the like.
> Do you think that the
Morrison could simply be much better sampled than virtually any other
formation? I know I have
> the most theropod taxa listed from it than
any other place in my stratigraphy file. Most Late Cretaceous North
> small theropods are known from partial
remains so that all troodontids are grouped as Troodon formosus and
> "velociraptorine" remains into
Saurornitholestes. Bambiraptor and a few other unnamed taxa are showing
> diversity of the latter is higher than
previously thought, which may hold true for other families as well.
We did consider the possibility that greater sampling
for the Morrison is a factor, but when we included all western North American
Campanian and Maastrichtian assemblages, which result in a greater overall
number of sites with greater geographic distribution and longer stratigraphic
coverage than the Morrison, the pattern holds. Similarly, the western
North American Campano-Maastrichtian assemblages have been worked for
comparable periods of exploration and by comparable number of teams as the
Morrison, and still the pattern holds.
It is quite likely, as you point out, that there are
multiple species currently recongized in "Troodon formosus" material,
and we have very good evidence for several different oviraptorosaurs, but that
still doesn't change the point that we have a situation in the Late K of North
America which is different from the Late J (or the Wessex Fm., or the
Bahariya, or what have you).
Note that this could all be overturned with future
> It is odd how
> pretty much all Late Cretaceous large theropods are
tyrannosauroids or abelisaurids though.
Indeed! Food for thought, and future
>> Actually, the Two Medicince Form
(which comes out as the sister to Daspletosaurus torosus) is not a
>> snouted form. This
is the form considered by Horner et al. (1992) to be transitional between
Daspletosaurus and T.
> Oops. Which is the
"long-snouted" daspletosaur specimen
conflations of several different *possible* new daspletosaurs out there.
Currie considers the Dinosaur Park Formation Daspletosaurus to be
distinct from D. torosus (from the earlier Oldman Fm.); if so, the
heavily restored "Albertosaurus libratus" specimen on display at the
Field Museum is probably a member of this species rather than
D. torosus. Note, however, that the teeth (and perhaps
even the tooth count) in this specimen are restored, rather than
original, and the cranial ornamentation was restored based on G.
libratus. Carr & Williamson are describing new
daspletosaur-like material for the American Southwest.
Bakker et al.
(1988) refer to the "strech-snout daspletosaur" in the Nanotyrannus
paper, but it is not identified in detail. Olshevsky (in the
Kyoryugaku Saizensen article) suggests that it is RTMP 81.9.1; if so,
this is a Horseshoe Canyon Fm. specimen being described by Phil
Thomas R. Holtz, Jr.
Department of Geology
Director, Earth, Life & Time
University of Maryland
College Park, MD
Phone: 301-405-4084 Email:
301-314-9661 Fax (CPS-ELT):