Triassic Herbivorous Dinosaurs

["R. Irmis" <rbi@dana.ucc.nau.edu>]

The following was mentioned in popular news articles that were posted onlist
earlier this year, but I cant remember seeing the abstract itself on list:

NORTH AMERICA?S OLDEST HERBIVOROUS DINOSAURS
HECKERT, Andrew B., Earth & Plan. Sci, Univ of New Mexico, Albuquerque, NM
87131, heckerta@unm.edu and LUCAS, Spencer G., New Mexico Museum of Nat
History & Sci, 1801 Mountain Rd NW, Albuquerque, NM 87104.
Recent microvertebrate collecting in the Upper Triassic Chinle Group of
Texas, New Mexico and Arizona demonstrates that herbivorous dinosaurs,
particularly ornithischians, were considerably more common during the early
Late Triassic than previously believed, whereas prosauropods remain limited
to a single occurrence. Furthermore, Late Triassic ornithischian dinosaurs
are both derived and diverse, with a variety of dental adaptations. At the
outset of this study, demonstrable early Late Triassic (Carnian)
ornithischian teeth were known from a handful of specimens collected at
three or four localities in the Chinle Group. Now, we recognize at least
eight ornithischian-bearing localities ranging in age from Otischalkian
(late early to early late Carnian) to Adamanian (latest Carnian) age in the
Chinle. These teeth represent at least five morphotypes: (1) a primitive,
recurved, coarsely denticled, possibly carnivorous ornithischian, (2) teeth
of Tecovasaurus murryi; (3) complex teeth with coarse denticles that are
themselves finely denticled; (4) the first teeth of Pekinosaurus olseni
discovered outside of the type locality in the Newark Supergroup of the
eastern USA; (5) fragmentary teeth that may represent the first occurrence
of Galtonia outside of its type locality in the Newark Supergroup; (6) tall,
asymmetrically denticled, recurved teeth that may represent the premaxillary
teeth of Tecovasaurus murryi.

These teeth have numerous biostratigraphic and evolutionary implications.
The occurrence of Tecovasaurus in no fewer than four localities of Adamanian
age indicates that Tecovasaurus is a potential index fossil of Adamanian
time. Records of Pekinosaurus and, possibly, Galtonia in the late Carnian
portion of both the Chinle and the Newark Supergroup strengthen existing
correlations of these strata. The putative carnivorous ornithischian is
known from two localities, both of Otischalkian age, and thus also appears
to have some biostratigraphic utility. From an evolutionary perspective, the
diversity and abundance of these teeth indicate that ornithischians probably
originated during the early Carnian and diversified rapidly during the late
Carnian.

Rocky Mountain (53rd) and South-Central (35th) Sections, GSA, Joint Annual
Meeting (April 29?May 2, 2001)
Session No. 12
Paleontology, Stratigraphy, and Sedimentology
Sheraton Old Town Hotel: Alvarado C
1:10 PM-5:00 PM, Tuesday, May 1, 2001