The postcranial anatomy of the Yacarerani boliviensis and the evolution of the notosuchian postcranial skeleton

LEARDI, J.M.; POL, DIEGO; NOVAS, F.; SUAREZ RIGLOS, M

Los Angeles, California

Congreso; SVP 73rd Annual Meeting; 2013

Los Angeles County Museum

Yacerarani boliviensis is a bizarre notosuchian whose remains were recovered form the Upper Cretaceous of Bolivia. This taxon is diagnosed by its peculiar cranial and, in particular, dental morphology. The block containing the holotype material also included several other individuals. The material studied belongs to at least three different individuals. This record is the first well-preserved and represented postcranial skeleton of any sphageasaurid notosuchian known. Few differences on the size of the elements recovered suggest a similar ontogenetic state of these individuals. The objective of this contribution is to study the postcranial skeleton of Yacarerani boliviensis and to evaluate the distribution of several postcranial characters among basal mesoeucrocodylians. The abundance of specimens allows a deep knowledge of Yacarerani?s postcranial skeleton, as a great number of elements are known. The axis is short and bears an anteroposteriolly short neural spine, as in most notosuchians. All cervical centra bear hypapophyses. As in other notosuchians, there is an abrupt migration of the parapophyses almost at the level of the diapophyses on the fifth dorsal vertebra. Knob-like hypapophyses are observed up to the seventh dorsal vertebra. There are forelimb characters shared with other notosuchians such as a greatly expanded scapular blade, the medially displaced deltopectoral crest of the humerus, the structure of the proximal end of the ulna, and the presence of an additional articular surface in the ulnare. Additionally, the hindlimb also bears relevant characters like a reduced fourth femoral trochanter on the femur that lacks an anterior flange, two additional depressions on the anterior hollow of the astragalus, and a posteroventral tuber on the calcaneum. Many postcranial characters have been previously identified as notosuchian synapomorphies, and new ones have been recovered as such in this contribution. This situation highlights the relevance of incorporating postcranial characters on the study of fossil crocodyliforms, as they can be phylogenetically informative.