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Nothronychus (therizinosaurian) braincase described



From: Ben Creisler
bcreisler@gmail.com

In the new issue of Journal of Vertebrate Paleontology:

David K. Smith (2014)
The braincase of the North American therizinosaurian Nothronychus
mckinleyi (Dinosauria, Theropoda).
Journal of Vertebrate Paleontology 34(3): 635-646
DOI:10.1080/02724634.2013.812097
http://www.tandfonline.com/doi/full/10.1080/02724634.2013.812097#.U2lYufldXeI

The description and comparison of the posterior braincase of
Nothronychus mckinleyi (MSM P-2117) from the Upper Cretaceous
(Turonian) Moreno Hills Formation of east-central New Mexico is
updated. As a result of the enlarged basicranial pneumatic system,
this region of the skeleton has undergone extensive rearrangement of
the cranial nerves and blood vessels from the plesiomorphic theropod
condition. Nothronychus and Falcarius possessed a number of
avian-associated characters or avian-trending characters in the
braincase and endocranium characteristic of highly derived
coelurosaurs. These traits, in some cases hypothesized, include the
posterior endocranium nearly filled with nervous tissue, a laterally
directed enlarged optic tectum, an enlarged flocculus, an intracranial
trigeminal ganglion, and the abducens canal entering the endocranium
separate from the infundibulum with no associated cavernous sinus. The
angle of the occipital plate with the basal plate of the basicranium
appears to be perpendicular and, therefore, intermediate between more
basal theropods and extant birds. However, the posterior endocranial
cavity does not appear flexed, which would result in a posteroventral
rotation of the endocranial cavity in Nothronychus, a character also
seen in the Cretaceous hesperornithiform bird Enaliornis and in
contrast to extant birds. Therefore, the evolution of the
coelurosaurian brain and braincase was trending in an avian direction
before the rest of the skeleton. The results presented here support
the model that therizinosaurs possessed weak bite forces as compared
to obligatory carnivorous theropods.