| Postcranial skeletal pneumaticity refers to invasion of bone by extensions from pulmonary air sacs; among extant amniotes this condition is limited to birds. The relative extent of pneumaticity varies among avian taxa, ranging from species lacking pneumatic postcrania to those pneumatizing the entire skeleton. Numerous explanations have been advanced to account for this variability (e.g., relative body size, diving behavior, etc.), however interspecific comparisons are traditionally limited to a few species and quantitative measures of pneumaticity are generally lacking. Moreover, based on a variety of osteological features (e.g., vertebral fossae and foramina) superficially similar to those found in the skeleton of extant birds, postcranial pneumaticity has been inferred for numerous extinct archosauromorph taxa, including pterosaurs, saurischian dinosaurs and primitive birds. These features have been interpreted to reflect an avian-style lung and air sac system, forming the basis for a variety of paleobiological inferences, particularly in theropod dinosaurs (e.g., pulmonary structure/function relationships, thermoregulation).; The goals of this project are twofold. First, it surveys a size- and behaviorally diverse clade of extant birds (Anseriformes), assessing the relative influences of body size, phylogeny, and behavioral specializations upon postcranial pneumaticity. To do so, one hundred anseriform species were examined. Regression analyses using phylogenetically independent contrasts do not indicate a clear relationship between body size and the degree of pneumaticity. Clade-specific patterns and diving behaviors may better predict relative pneumaticity in this group, with reduced pneumaticity exhibited by diving taxa.; Secondly, extant archosaur taxa were examined to identify criteria that may be used to infer pneumatic features in fossil specimens. Results suggest that certain morphological features are consistent with pneumatic invasion of bone (e.g., foramina leading to large internal chambers). Other features, such as vertebral fossae, are associated with a variety of soft tissue types (e.g., muscle, adipose), serving limited utility for detecting pneumaticity in fossil specimens. Based on the criteria established in this study, there is insufficient evidence for pneumaticity in certain fossil taxa such as Erythrosuchus africanus, and strong evidence of pneumatic postcrania in others (e.g., pterosaurs and saurischian dinosaurs such as the theropod Majungatholus atopus). |
