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Small Theropod Teeth from Late Cretaceous of New Mexico

From: Ben Creisler

New in PLoS ONE:

Thomas E. Williamson & Stephen L. Brusatte (2014)
Small Theropod Teeth from the Late Cretaceous of the San Juan Basin,
Northwestern New Mexico and Their Implications for Understanding
Latest Cretaceous Dinosaur Evolution.
PLoS ONE 9(4): e93190.

Studying the evolution and biogeographic distribution of dinosaurs
during the latest Cretaceous is critical for better understanding the
end-Cretaceous extinction event that killed off all non-avian
dinosaurs. Western North America contains among the best records of
Late Cretaceous terrestrial vertebrates in the world, but is biased
against small-bodied dinosaurs. Isolated teeth are the primary
evidence for understanding the diversity and evolution of small-bodied
theropod dinosaurs during the Late Cretaceous, but few such specimens
have been well documented from outside of the northern Rockies, making
it difficult to assess Late Cretaceous dinosaur diversity and
biogeographic patterns. We describe small theropod teeth from the San
Juan Basin of northwestern New Mexico. These specimens were collected
from strata spanning Santonian - Maastrichtian. We grouped isolated
theropod teeth into several morphotypes, which we assigned to
higher-level theropod clades based on possession of phylogenetic
synapomorphies. We then used principal components analysis and
discriminant function analyses to gauge whether the San Juan Basin
teeth overlap with, or are quantitatively distinct from, similar tooth
morphotypes from other geographic areas. The San Juan Basin contains a
diverse record of small theropods. Late Campanian assemblages differ
from approximately co-eval assemblages of the northern Rockies in
being less diverse with only rare representatives of troodontids and a
Dromaeosaurus-like taxon. We also provide evidence that erect and
recurved morphs of a Richardoestesia-like taxon represent a single
heterodont species. A late Maastrichtian assemblage is dominated by a
distinct troodontid. The differences between northern and southern
faunas based on isolated theropod teeth provide evidence for
provinciality in the late Campanian and the late Maastrichtian of
North America. However, there is no indication that major components
of small-bodied theropod diversity were lost during the Maastrichtian
in New Mexico. The same pattern seen in northern faunas, which may
provide evidence for an abrupt dinosaur extinction.