The extremely thin ilium of the sauropod dinosaur Cathartesaura anaerobica Gallina and Apesteguía 2005 (Sauropoda, Diplodocoidea) with comments on the pneumatization of the rebbachisaurid hip

Cathartesaura anaerobica (Gallina and Apesteguía 2005) is a rebbachisaur sauropod from Huincul Formation(upper Cenomanian-Turonian) of Río Negro province, Argentina. It is represented by a cervical vertebra, twocaudal vertebrae, a scapula, an ilium and a femur. Here, we redescribe the left ilium of Cathartesaura. Theventral part of the pre-acetabular process, the pubic peduncle and the acetabular margin are robust whilethe iliac blade is extremely thin and laminar. The presence of several U-shaped depressions between thetransverse processes on medial aspect are supporting the hypothesis that the diverticula of the abdominalair sac could invade the space within the sacral vertebrae and the ilium as was reported in Amazonsaurus,Tataouinea and Campananeyen. Cathartesaura was found at rocks of the Kokorkom paleodesert during theCretaceous Thermal Maximum. It is very likely that the invasion of the abdominal air sac provides resistanceto the extreme thin ilium during and/or also reduced bone density to decrease the energetic cost oflocomotion as an advantage for warm climates as previously thought.