AIR-SPACE PROPORTIONS IN THE PNEUMATIC AXIAL AND APPENDICULAR SKELETON OF A TITANOSAUR SAUROPOD FROM THE UPPER CRETACEOUS OF TEXAS

Sauropod dinosaurs attained the greatest body sizes of any terrestrial animals. They were likely aided in reaching such large sizes by the presence of skeletal pneumaticity, the replacement of some bone volume with air space, resulting in a lower body mass. The magnitude of pneumatization can be quantified as the air-space proportion (ASP) of a bone relative to the bone’s total volume. ASP has been measured in a variety of sauropod taxa, but sampling is as yet insufficient to conclude whether ASP varies consistently from one taxon to another and how it differs between body regions. Solving these problems is a necessary step towards understanding the role of pneumaticity in sauropod body mass evolution.

This study extends both the taxonomic and anatomic sampling of sauropod ASP by examining a titanosaur sauropod from the Upper Cretaceous of Texas, which features a pneumatic ilium as well as vertebrae and ribs. ASP was measured from naturally broken sections, which were manually digitized to distinguish air space from bone. Calculations of ASP were conducted in ArcGIS. Values ranged from 0.55 to almost 0.80 in dorsal vertebrae and from 0.40 to almost 0.80 for the ilium. These values are consistent with previously studied sauropod taxa, supporting prior claims that titanosaur ASP was similar to that of other sauropods despite having a different internal organization of the air space (i.e., camellate vs. camerate pneumaticity). Variation was greater within individual bones than between sampled skeletal regions, highlighting the need to integrate data from multiple sections when estimating the ASP of a single bone.