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Pneumatization in the Cervical Column of the Ostrich as Clue to Dinosaur Anatomy

Ben Creisler

>From PLoS ONE:

Naomi E. Apostolaki , Emily J. Rayfield & Paul M. Barrett (2015)
Osteological and Soft-Tissue Evidence for Pneumatization in the
Cervical Column of the Ostrich (Struthio camelus) and Observations on
the Vertebral Columns of Non-Volant, Semi-Volant and Semi-Aquatic
PLoS ONE 10(12): e0143834.

Postcranial skeletal pneumaticity (PSP) is a condition most notably
found in birds, but that is also present in other saurischian
dinosaurs and pterosaurs. In birds, skeletal pneumatization occurs
where bones are penetrated by pneumatic diverticula, membranous
extensions that originate from air sacs that serve in the ventilation
of the lung. Key questions that remain to be addressed include further
characterizing (1) the skeletal features that can be used to infer the
presence/absence and extent of PSP in birds and non-avian dinosaurs,
and (2) the association between vertebral laminae and specific
components of the avian respiratory system. Previous work has used
vertebral features such as pneumatic foramina, fossae, and laminae to
identify/infer the presence of air sacs and diverticula, and to
discuss the range of possible functions of such features. Here, we
tabulate pneumatic features in the vertebral column of 11 avian taxa,
including the flightless ratites and selected members of semi-volant
and semi-aquatic Neornithes. We investigate the associations of these
osteological features with each other and, in the case of Struthio
camelus, with the specific presence of pneumatic diverticula. We find
that the mere presence of vertebral laminae does not indicate the
presence of skeletal pneumaticity, since laminae are not always
associated with pneumatic foramina or fossae. Nevertheless, laminae
are more strongly developed when adjacent to foramina or fossae. In
addition, membranous air sac extensions and adjacent musculature share
the same attachment points on the vertebrae, rendering the use of such
features for reconstructing respiratory soft tissue features
ambiguous. Finally, pneumatic diverticula attach to the margins of
laminae, foramina, and/or fossae prior to their intraosseous course.
Similarities in PSP distribution among the examined taxa are
concordant with their phylogenetic interrelationships. The possible
functions of PSP are discussed in brief, based upon variation in the
extent of PSP between taxa with differing ecologies.