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

Ornithomimosaurian metatarsal from Cretaceous of Alaska

From: Ben Creisler

In the new issue of JVP:

Akinobu Watanabe, Gregory M. Erickson & Patrick S. Druckenmiller (2013)
An ornithomimosaurian from the Upper Cretaceous Prince Creek Formation
of Alaska.
Journal of Vertebrate Paleontology 33(5): 1169-1175

Polar dinosaurs provide unique insights for testing hypotheses
regarding paleobiology, paleoecology, and paleobiogeography. Critical
for such testing is a comprehensive understanding of the taxonomic
diversity of contemporaneous polar and lower-latitude paleofaunas.
Here we determine the taxonomic identity of a theropod metatarsal that
was discovered in the Upper Cretaceous Prince Creek Formation on the
North Slope of Alaska. Its morphology and size are most consistent
with a metatarsal IV of an ornithomimosaurian or a juvenile
tyrannosaurid. Long bone histological analysis reveals a bone tissue
composed of fibrolamellar matrix with a mosaic of laminar,
longitudinal, sub-plexiform, radiating, and reticular vascularization
patterns. The spacing between two outer growth lines diminishes near
the periosteal surface, suggesting that the individual was near
somatic maturity at the time of death. This finding suggests that its
adult body size was comparable to contemporaneous North American
ornithomimids, such as Ornithomimus, and much smaller than those of
known tyrannosaurids. Thus, we ascribe the Alaskan specimen to
Ornithomimosauria, providing new evidence on the known taxonomic
diversity of the Prince Creek fauna. Interestingly, the Alaskan
specimen primarily shows annuli, which is inconsistent with the
pronounced lines of arrested growth (LAGs) reported in the purported
southern high-latitude ornithomimosaurian Timimus and observed
variably in contemporaneous lower-latitude ornithomimids. Due to this
inconsistency, additional dinosaurian specimens are needed to
comprehensively examine the relevance of particular histological
features to polar climate habitation.