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Nomenclature for external pneumatic structures on saurischian vertebrae

From: Ben Creisler

A new paper in PLoS One:

Wilson, J.A., D'Emic, M.D., Ikejiri, T., Moacdieh, E.M., Whitlock, J.A.,
A Nomenclature for Vertebral Fossae in Sauropods and Other Saurischian
PLoS ONE 6(2): e17114. doi:10.1371/journal.pone.0017114 


The axial skeleton of extinct saurischian dinosaurs (i.e., theropods,
sauropodomorphs), like living birds, was pneumatized by epithelial
outpocketings of the respiratory system. Pneumatic signatures in the
vertebral column of fossil saurischians include complex branching chambers
within the bone (internal pneumaticity) and large chambers visible
externally that are bounded by neural arch laminae (external pneumaticity).
Although general aspects of internal pneumaticity are synapomorphic for
saurischian subgroups, the individual internal pneumatic spaces cannot be
homologized across species or even along the vertebral column, due to their
variability and absence of topographical landmarks. External pneumatic
structures, in contrast, are defined by ready topological landmarks
(vertebral laminae), but no consistent nomenclatural system exists. This
deficiency has fostered confusion and limited their use as character data
in phylogenetic analysis.

Methodology/Principal Findings
We present a simple system for naming external neural arch fossae that
parallels the one developed for the vertebral laminae that bound them. The
nomenclatural system identifies fossae by pointing to reference landmarks
(e.g., neural spine, centrum, costal articulations, zygapophyses). We
standardize the naming process by creating tripartite names from ?primary
landmarks,? which form the zygodiapophyseal table, ?secondary landmarks,?
which orient with respect to that table, and ?tertiary landmarks,? which
further delineate a given fossa.

The proposed nomenclatural system for lamina-bounded fossae adds clarity to
descriptions of complex vertebrae and allows these structures to be sourced
as character data for phylogenetic analyses. These anatomical terms denote
potentially homologous pneumatic structures within Saurischia, but they
could be applied to any vertebrate with vertebral laminae that enclose
spaces, regardless of their developmental origin or phylogenetic

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