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Pneumaticity in pterosaur limb bones
From: Ben Creisler
New in PLoS ONE:
Elizabeth G. Martin & Colin Palmer (2014)
Air Space Proportion in Pterosaur Limb Bones Using Computed Tomography
and Its Implications for Previous Estimates of Pneumaticity.
PLoS ONE 9(5): e97159.
Air Space Proportion (ASP) is a measure of how much air is present
within a bone, which allows for a quantifiable comparison of
pneumaticity between specimens and species. Measured from zero to one,
higher ASP means more air and less bone. Conventionally, it is
estimated from measurements of the internal and external bone
diameter, or by analyzing cross-sections. To date, the only pterosaur
ASP study has been carried out by visual inspection of sectioned bones
within matrix. Here, computed tomography (CT) scans are used to
calculate ASP in a small sample of pterosaur wing bones (mainly
phalanges) and to assess how the values change throughout the bone.
These results show higher ASPs than previous pterosaur pneumaticity
studies, and more significantly, higher ASP values in the heads of
wing bones than the shaft. This suggests that pneumaticity has been
underestimated previously in pterosaurs, birds, and other archosaurs
when shaft cross-sections are used to estimate ASP. Furthermore, ASP
in pterosaurs is higher than those found in birds and most sauropod
dinosaurs, giving them among the highest ASP values of animals studied
so far, supporting the view that pterosaurs were some of the most
pneumatized animals to have lived. The high degree of pneumaticity
found in pterosaurs is proposed to be a response to the wing bone
bending stiffness requirements of flight rather than a means to reduce
mass, as is often suggested. Mass reduction may be a secondary result
of pneumaticity that subsequently aids flight.