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Tyrannosaurid metatarsal from Baja California, Mexico

From: Ben Creisler

New online for Acta Palaeontologica Polonica:

Brandon R. Peecook, Jeffrey A. Wilson, René Hernández-Rivera, Marisol
Montellano-Ballesteros, and Gregory P. Wilson (2012)
First tyrannosaurid remains from the Upper Cretaceous "El Gallo"
Formation of Baja California, México.
Acta Palaeontologica Polonica (in press)
doi: http://dx.doi.org/10.4202/app.2012.0003

We report a complete left fourth metatarsal collected from rocks of
the Upper Cretaceous (Campanian) "El Gallo" Formation exposed along
the Pacific Ocean near El Rosario, Baja California, México. The
metatarsal IV was part of an arctometatarsalian metatarsus, as
evidenced by a deep medial notch proximally and extensive articulation
for metatarsal III. This condition, along with the U-shape of the
proximal end, supports identification as tyrannosauroid. It is
assigned to Tyrannosauridae based on features on the posterior surface
of the shaft, but finer taxonomic resolution is not possible. Compared
to other tyrannosauroids, the metatarsal is relatively short, closely
resembling the proportions of the gracile Albertosaurus sarcophagus
rather than the much more massive, robust metatarsals of Tyrannosaurus
rex. The Baja tyrannosaurid metatarsal is shorter than almost all
other tyrannosauroid fourth metatarsals, raising the possibility that
it pertains to an immature individual. North American tyrannosauroids
are best known from the northern coast of the Western Interior Seaway,
as well as less frequently on the southern coast of the seaway in Utah
and New Mexico. The new record in Baja marks the first unambiguous
skeletal material
of a tyrannosaurid both in México and along the Pacific coast.