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Acristavus, new hadrosaurine hadrosaur from Montana and Utah

From: Ben Creisler

In new Journal of Vertebrate Paleontology:

Terry A. Gates, John R. Horner, Rebecca R. Hanna & C. Riley Nelson (2011)
New unadorned hadrosaurine hadrosaurid (Dinosauria, Ornithopoda) from the
Campanian of North America.
Journal of Vertebrate Paleontology 31(4):798-811

A new hadrosaurid dinosaur, Acristavus gagslarsoni, is here named on the
basis of several autapomorphic characteristics of the frontal, postorbital,
and dentary. Acristavus is a member of the newly erected clade
Brachylophosaurini, which along with its other members, Brachylophosaurus
and Maiasaura, constitutes the earliest hadrosaurine hadrosaurid clade. The
new taxon occurred approximately 79 million years ago and has been
recovered from the Two Medicine Formation of western Montana and nearly
simultaneously in the Wahweap Formation of southern Utah. Corresponding
with its age and relationship to the other members of the
Brachylophosaurini, it is not surprising that Acristavus possesses traits
seen in both Brachylophosaurus and Maiasaura, but not necessarily shared
between them. One of the most interesting morphological features of
Acristavus is the lack of cranial osteological ornamentation, which is in
stark contrast to every other hadrosaurid dinosaur except Edmontosaurus.
Combining stratigraphic and phylogenetic data from Acristavus yields
support for the hypothesis that the hadrosaurid ancestor did not possess
cranial ornamentation, and that the subfamilies Hadrosaurinae and
Lambeosaurinae each independently developed display structures.

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