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Braincases of Carnotaurus and Falcarius (new JVP)
From: Ben Creisler
bh480@scn.org
A couple of new articles on theropod braincases in the
March 2011 Journal of Vertebrate Paleontology:
Carabajal, Ariana Paulina, 2011
The braincase anatomy of Carnotaurus sastrei (Theropoda:
Abelisauridae) from the Upper Cretaceous of Patagonia
Journal of Vertebrate Paleontology 31(2): 378 - 386
DOI: 10.1080/02724634.2011.550354
http://www.informaworld.com/smpp/content~db=all~content=a9
35220610~frm=titlelink
Abstract
Carnotaurus sastrei is a large abelisaurid dinosaur from
the Upper Cretaceous of Patagonia. Its remains include an
almost complete skeleton with a well-preserved skull and
braincase. Because relatively few abelisaurid braincases
are known, the description of the Carnotaurus braincase
is important for understanding the variability of this
complex structure within the clade. Carnotaurus exhibits
traits that characterize the abelisaurid basicranium,
such as a well-developed preotic pendant, solid
basipterygoid processes, and pneumatic basisphenoid,
subsellar, and lateral tympanic recesses. The
basipterygoid processes do not project laterally, unlike
the divergent processes observed in other abelisaurids.
Carnotaurus shares with the Malagasy abelisaurid
Majungasaurus crenatissimus caudodorsally oriented
paroccipital processes and a maxillomandibular foramen
for the trigeminal nerve that in lateral view is aligned
with the nuchal crest. The detailed description of the
braincase of Carnotaurus presented here provides a better
cranial anatomical record of this Patagonian abelisaurid
and preliminary insights to the neurocranial morphology
within the group.
Smith, David K.; Lindsay E. Zanno; R. Kent Sanders;
Donald D. Deblieux; James I. Kirkland, 2011
New information on the braincase of the North American
therizinosaurian (Theropoda, Maniraptora) Falcarius
utahensis.
Journal of Vertebrate Paleontology 31(2): 387 - 404
DOI: 10.1080/02724634.2011.549442
http://www.informaworld.com/smpp/content~db=all~content=a9
35221232~frm=titlelink
Abstract
Many disarticulated bones from multiple individuals of a
primitive therizinosaurian, referred to Falcarius
utahensis, were found in the paucispecific Crystal Geyser
bonebed in the Lower Cretaceous Cedar Mountain Formation
of eastern Utah. To date, more than 2000 specimens from
this species have been excavated. Included in this
collection are two partial braincases, one of which is
designated the holotype. Here we describe the braincase
morphology of Falcarius utahensis. These specimens help
establish the primitive cranial condition for the
Therizinosauria and further substantiate intraspecific
and contralateral braincase pneumatic variation in
theropods. When combined with new observations on the
cranial remains of the therizinosaurid Nothronychus
mckinleyi derived from computed tomographic (CT) scans,
the braincase morphology of Falcarius clarifies several
evolutionary trends within the Therizinosauria and
establishes a suite of synapomorphies for the
Therizinosauridae. Trends within the clade include
increased basicranial pneumatization (the development of
a basisphenoid bulla and loss of external subcondylar
recesses), anterior deflection of the supraoccipital, and
the reduction of points of origin of the craniocervical
musculature, associated with the loss of discrete
basipterygoid processes, probably due to incorporation of
these structures into the expanded hyperpneumatic bone.
Finally, CT scans reveal a complete, nearly avian, inner
ear with bird-like semicircular canals and a long cochlea
indicating broad frequency discrimination.