Meeting Abstract
Pneumaticity refers to the hollow space within skeletal tissue caused by the invasion of the diverticula of respiratory air sacs. Pneumatic bones are present in many archosaur groups, but postcranial skeletal pneumaticity is well developed in three of these groups: pterosaurs, sauropodomorphs, and theropods. The degree of pneumaticity can be quantified by the Air Space Proportion (ASP), which is a measure of the ratio of air space (represented in fossils by the infilling of matrix) to skeletal tissue. Initially, ASP in fossil bones was measured in places where fortuitous breaks allowed visualization of the internal bone. More recently, ASP has been measured in fossil bones using micro-computed tomography (µ-CT), which is a non-destructive means of accessing the internal structure of a bone. This method has been applied to pterosaur fossils, for which ASP was measured in a representative sample of slices, accounting for trabecular bone at the articulations and excluding struts in the shaft of the bone. We have developed a new method that calculates the volumetric proportion of air and bone (volumetric ASP, or vASP) from three-dimensional (3D) models reconstructed from µ-CT scans using the program Mimics. Here we report the application of this method to pterosaur and avian wing bones. Using this method, we estimate an average vASP of 96.8% in two pterosaur humeri and 62.1% in five hummingbird humeri (genera Archilocus and Calliphlox). The use of Mimics provides faster segmentation of fossils and modern bone than previous methods. This new method maximizes the amount of preserved skeletal tissue accounted for in ASP calculation, while still providing slice by slice information, and produces 3D models that will be used for further study of the biomechanical properties of pneumatic bones.
