Caudal pneumaticity and pneumatic hiatuses in the sauropod dinosaurs Giraffatitan and Apatosaurus

28th September 2010

Mathew J. Wedel1 and Michael P. Taylor2
1College of Osteopathic Medicine of the Pacific and College of Podiatric Medicine, Western University of Health Sciences, 309 E. Second Street, Pomona, California 91766-1854. E-mail: <>
2Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom. E-mail: <>

Skeletal pneumaticity is present in the presacral vertebrae of most sauropod dinosaurs, but pneumatic cavities are less common in the vertebrae of the tail: prominent caudal pneumaticity is restricted to diplodocines and saltasaurines. We describe previously overlooked pneumatic fossae in mid-caudal vertebrae of Giraffatitan and Apatosaurus. In both taxa, the most distal pneumatic vertebrae are separated from other pneumatic vertebrae by sequences of three to seven bilaterally apneumatic vertebrae. These gaps in pneumatization constitute pneumatic hiatuses, which until now were assumed to divide separate pneumatizing diverticula. Caudal pneumaticity is not prominent in most individuals of either taxon, and its unpredictable development means that it may be more taxonomically widespread than previously recognized within Sauropoda and elsewhere in Saurischia. The erratic patterns of caudal pneumatization in Giraffatitan and Apatosaurus, including asymmetry and the pneumatic hiatuses, show that pneumatic diverticula were more broadly distributed in the bodies of the living animals than are their traces in the skeleton. Together with recently published evidence of subcutaneous diverticula in pterosaurs, this shows that pneumatic diverticula in ornithodirans are underdetermined by their skeletal traces, and suggests that their prevalence has been systematically underestimated.

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