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Ceratopsian head size, weaponry, and cervical adaptation hypotheses

Ben Creisler

A new online paper:

Collin S. VanBuren, Nicolás E. Campione and David C. Evans (2015)
Head size, weaponry, and cervical adaptation: testing craniocervical
evolutionary hypotheses in Ceratopsia.
Evolution (advance online publication)
DOI: 10.1111/evo.12693

The anterior cervical vertebrae form the skeletal connection between
the cranial and postcranial skeletons in higher tetrapods. As a
result, the morphology of the atlas-axis complex is likely to be
shaped by selection pressures acting on either the head or neck. The
neoceratopsian (Reptilia:Dinosauria) syncervical represents one of the
most highly modified atlas-axis regions in vertebrates, being formed
by the complete coalescence of the three most anterior cervical
vertebrae. In ceratopsids, the syncervical has been hypothesized to be
an adaptation to support a massive skull, or to act as a buttress
during intraspecific head-to-head combat. Here we test these
functional/adaptive hypotheses within a phylogenetic framework, and
critically examine the previously proposed methods for quantifying
relative head size in the fossil record for the first time. Results
indicate that neither the evolution of cranial weaponry nor large head
size correlates with the origin of cervical fusion in ceratopsians,
and we, therefore, reject both adaptive hypotheses for the origin of
the syncervical. Anterior cervical fusion has evolved independently in
a number of amniote clades, and further research on extant groups with
this peculiar anatomy is needed to understand the evolutionary basis
for cervical fusion in Neoceratopsia