P1.99 Wednesday, Jan. 4 Postcranial Pneumaticity and Bone Structure in Two Clades of Neognath Birds GUTZWILLER, S.G.*; O'CONNOR, P.M.; SU, A.; The Ohio State University; Ohio University; Cleveland State University email@example.com
Some living birds exhibit postcranial skeletal pneumaticity, aeration of the postcranial skeleton by the pulmonary air sacs. The extent of pneumaticity can vary, ranging from taxa that are completely apneumatic to those with air filling most of the postcranial skeleton. This project examined the influence of skeletal pneumatization on bone structural parameters in a size- and locomotor-diverse (e.g., diving vs. soaring) assemblage of neognath birds (charadriiforms and pelecaniforms). Results for pelecaniforms suggest that specialized dive foragers (e.g., the apneumatic anhinga) tend to have thicker cortical bone and a higher trabecular bone volume fraction. Conversely, Pelecanus occidentalis, the taxon with pneumatic vertebrae, the largest body size, and specializations for soaring flight, exhibits thinner cortical bone and a lower trabecular bone volume fraction. Such patterns in bone structural parameters are here interpreted to pertain to decreased buoyancy in birds specialized in dive foraging and decreased skeletal density in birds of larger body size, particularly those with specialized flight behaviors. The potential to differentially pneumatize the postcranial skeleton and alter bone structure may have played a role in relaxing constraints on body size evolution and/or habitat exploitation during the course of avian evolution. Notably, no patterns were observed within charadriiforms, indicating that the relationship between pneumaticity and bone structure is variable among different clades of birds.