Meeting Abstract

P1.147  Monday, Jan. 4  Body Plan Evolution in Birds: Postcranial Skeletal Pneumaticity and its Role in Relaxing Constraints on Body Size and Locomotor Potential OCONNOR, Patrick*; GUTZWILLER, Sarah; Ohio University; Ohio University oconnorp@ohiou.edu

Extant birds represent the only living sauropsid group in which pulmonary air sacs aerate the postcranial skeleton. The degree of variability in birds is notable, ranging from taxa that are completely apneumatic to those characterized by air within most of the postcranial skeleton. Although numerous factors (e.g., body size) have been linked with ‘relative’ pneumaticity, comparative studies examining this system remain limited. This project sought to (1) examine whole-body patterns of pneumaticity in select nonpasseriform neognath birds and (2) evaluate relationships among relative pneumaticity, body size and locomotor specializations (e.g. diving, soaring). Species-specific pneumaticity profiles were established for 68 species representing 10 higher-level groups. Although comparisons reveal relatively conserved patterns within most lower-level clades, both size-threshold and locomotor behavior impart predictable deviations from the clade norm. For example, the largest flying birds (bustards, vultures, pelicans) exhibit hyperpneumaticity relative to smaller members of their respective clades. In contrast, skeletal pneumaticity has been independently lost in multiple lineages of diving specialists (e.g., loons, penguins, diving ducks). Such reductions in skeletal pneumaticity result in decreased buoyancy in birds specialized for dive foraging. Conversely, aerating the postcranial skeleton offers a mechanism that allows volumetric increases in bone (and thus, the underlying support framework dictating whole-body volume) without concomitant increases in body mass. Thus, the potential to differentially pneumatize the postcranial skeleton may have played a role in relaxing constraints on body size evolution and/or habitat exploitation during the course of avian evolution.