RE: Nemegtian tyrannosaurs

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Jaime A. Headden
>
>   I think this interpretation is error, based on the nature of the Hell
> Creek sedimentology, focusing on highland and savannah-type regions, with
> low tree density.

This doesn't jive with, among others, Retallack's paleosol work (e.g.,
Rettallack, G.J. 1997. DinoFest volume), where he points out that the
mollisols typical of wooded grasslands and savannas or inceptisols and
vertisols expected from angiosperm or fern scrublands are missing in the
Hell Creek.  His reconstruction for the Hell Creek Formation environment is
a tropical woodland with local cypress swamps.

> However, the "bayou"-like environments of the Nemegt and
> Dinosaur Park/Judith River Formations are much more heavily wooded,

Again, not so (for the North American ones, at least) by Retallack's
studies.

> not
> the other way around. The Nemegt was not at all a "desert-like"
> environment 75mya, but very, very wet.

Best analog for the Nemegt I've seen is the Okavango delta in Africa.

>   Incidentally, the Two Medicince is almost certainly the same formation
> as the Judith River Formation, separated almost entirely by the Montana
> state line.
>
Actually, both the true Judith River Fm. (including the type locality) and
the Two Medicine are found in Montana.  The Judith River is found in eastern
Montana (east of the Sweetgrass arch), and the Two Medicine in the west.
They are pretty well recognized as the lowland and upland components of the
same clastic wedge: however, because they ARE lithologically distinct, they
make reasonably good formations.

The questions are really whether:
a) any of the Albertan formations (Foremost, Oldman, and Dinosaur Park) are
synonymous with either the Two Med and/or the Judith River, and
b) the "Judith River Group" of Alberta should be renamed...  Heck, I think
one could argue for a "Belly River Group" containing the Two Medicine,
Judith River, Foremost, Oldman, and Dinosaur Park).

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796