Most living birds exhibit some degree of postcranial skeletal pneumaticity, aeration of the postcranial skeleton by pulmonary air sacs and/or directly from the lungs. The extent of pneumaticity varies greatly, ranging from taxa that are completely apneumatic to those with air filling most of the postcranial skeleton. This study examined the influence of skeletal pneumatization on bone structural parameters in a sample of two size-and foraging-style diverse (e.g., subsurface diving vs. soaring specialists) clades of neognath birds (charadriiforms and pelecaniforms). Cortical bone thickness and trabecular bone volume fraction were assessed in one cervical and one thoracic vertebra in each of three pelecaniform and four charadriiform species. Results for pelecaniforms indicate that specialized subsurface dive foragers (e.g., the apneumatic anhinga) have thicker cortical bone and a higher trabecular bone volume fraction than their non-diving clademates. Conversely, the large-bodied, extremely pneumatic brown pelican (Pelecanus occidentalis) 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 subsurface dive foraging and decreased skeletal density (at the whole bone level) in birds of larger body size. 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, similar patterns were not observed within the equally diverse charadriiforms, suggesting that the relationship between pneumaticity and bone structure is variable among different clades of neognath birds. Anat Rec, 296:867-876,

The evolution of mammalian molars has been marked by transitions representing significant changes in shape and function. One such transition is the addition and elaboration of the talon, the distolingual region of the ancestral tribosphenic upper molar of therian mammals and some extinct relatives. This study uses suborder Microchiroptera as a case study to explore the adaptive implications of the expansion of the talon on the tribosphenic molar, specifically focusing on the talon's role in the compression and shear of food during breakdown. Three-dimensional computer renderings of casts of the upper left first molars were created for microbat species of a variety of dietary categories (frugivore, etc.) and physical properties of food (hard and soft). Relief Index (RFI) was measured to estimate the topography and function of the whole tooth and of the talon and trigon (the remaining primitive tribosphenic region) individually, in order to examine 1) how the shape of the whole tooth, trigon, and talon reflects the compromise between their crushing and shearing functions, 2) how whole tooth, trigon, and talon function differs according to diet, and 3) how the presence of the talon affects overall molar function. Results suggest that RFI of both the whole tooth and the trigon varies according to dietary groups, with frugivores having greater crushing function when compared with the other groups. The talon, however, consistently has low RFI (a flatter topography), and its presence lowers the RFI of the whole tooth across all dietary categories, suggesting that the talon is primarily functioning in crushing during food breakdown. The potential benefits of a crushing talon for microbats of various dietary groups are discussed.