[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

A couple of recent theropod papers...

Anat Rec A Discov Mol Cell Evol Biol. 2005

Dental morphology and variation in theropod dinosaurs:
Implications for the taxonomic identification of
isolated teeth.

Smith JB, Vann DR, Dodson P.

Department of Earth and Environmental Science,
University of Pennsylvania, Philadelphia,

Isolated theropod teeth are common Mesozoic fossils
and would be an important data source for paleoecology
biogeography if they could be reliably identified as
having come from particular taxa. However, obtaining
identifications is confounded by a paucity of easily
identifiable characters. Here we discuss a
quantitative methodology designed to provide
defensible identifications of isolated teeth using
Tyrannosaurus as a comparison taxon. We created a
standard data set based as much as possible on teeth
of known taxonomic affinity against which to compare
isolated crowns. Tooth morphology was described using
measured variables describing crown length, base
length and width, and derived variables related to
basal shape, squatness, mesial curve shape, apex
location with respect to base, and denticle size.
Crown curves were described by fitting the power
function Y = a + bX(0.5) to coordinate data collected
from lateral-view images of mesial curve profiles. The
b value from these analyses provides a measure of
curvature. Discriminant analyses compared isolated
teeth of various taxonomic affinities against the
standard. The analyses classified known Tyrannosaurus
teeth with Tyrannosaurus and separated most teeth
known not to be Tyrannosaurus from Tyrannosaurus. They
had trouble correctly classifying teeth that were very
similar to Tyrannosaurus and for which there were few
data in the standard. However, the results indicate
that expanding the standard should facilitate the
identification of numerous types of isolated theropod
Proc Biol Sci. 2005 Jun 7;272(1568):1179-1183.   

Early development of the facial region in a non-avian
theropod dinosaur.

Rauhut OW, Fechner R.

Bayerische Staatssammlung fur Palaontologie und
Geologie, Richard-Wagner-Strasse 10, 80333 Munchen,

An isolated maxilla of the theropod dinosaur
Allosaurus from the Late Jurassic (the Kimmeridgian,
153 million years ago) of Portugal is the first
cranial remain of a non-coelurosaurian theropod
hatchling reported so far, and sheds new light on the
early cranial development of non-avian theropods.
Allosaurus hatchlings seem to have been one-seventh or
less of the adult length and are thus comparable in
relative size to hatchlings of large extant crocodile
species, but are unlike the relatively larger
hatchlings in coelurosaurs. The snout experienced
considerable positive allometry and an increase in
tooth count during early development. The element is
especially noteworthy for the abundant and
well-developed features associated with the paranasal
pneumatic system. Pneumatic structures present include
all those found in adult allosaurids and most are even
more developed than in adult skulls. Together with
evidence on the ontogeny of the tympanic pneumatic
system in allosaurids, these findings demonstrate that
cranial pneumaticity developed early in theropod
ontogeny. The strong development of pneumatic features
in early ontogenetic stages of non-avian theropods
supports the hypothesis that pneumatization of cranial
bones was opportunistic and indicates that
heterochrony played an important role in the evolution
of craniofacial pneumaticity in this group.