OCONNOR, P.M.; Ohio University College of Osteopathic Medicine: Pulmonary Pneumaticity in the Postcranial Skeleton of Extant Anseriforms

Anseriform birds were surveyed to examine how the degree of postcranial pneumaticity varies in a behaviorally and size-diverse clade of birds. This study attempts to extricate the relative effects of phylogeny, body size, and behavioral specializations (e.g., diving) that have been postulated to influence the extent of postcranial skeletal pneumaticity. One hundred anseriform species were examined as the focal study group. Methods included latex injection of the pulmonary apparatus followed by gross dissection or direct examination of osteological specimens. The Pneumaticity Index (PI) is introduced as a means of quantifying and comparing postcranial pneumaticity in a number of species simultaneously. Phylogenetically independent contrasts were used to examine the relationship between body size and the degree of postcranial pneumaticity throughout the anseriform clade. There is a high degree of similarity within most anseriform subgroups. As a whole, Anseriformes demonstrate no significant relationship between relative pneumaticity and body size, as indicated by regression analysis of body mass on pneumaticity index. It is apparent, however, that many clades of diving ducks do exhibit lower pneumaticity indices than their nondiving relatives. Only by exclusion of diving taxa from analyses is a significantly positive relationship observed, and the hypothesis of relatively higher pneumaticity in larger-bodied birds is weakly supported. However, low correlations indicate that factors other than body size account for much of the variation observed in relative pneumaticity. Enigmatic pneumatic features located in distal limb forelimb elements of anhimids result from invasion of bone by a network of subcutaneous air sac diverticula spreading distally along the wings.