A new basal sauropodomorph from South Africa with comments on non- ‐sauropod sauropodiforms

ALEJANDRO OTERO; DIEGO POL; ANUSUYA CHINSAMY; JONAH CHOINIERE

Mendoza

Congreso; 4th International Paleontological Congress; 2014

We present a new basal sauropodomorph from South Africa. The specimen (BP/1/386) was collected by A.W. Keyser from outcrops of the Late Triassic-Early Jurassic Elliot Formation, near the South African town of Zastron, between 1936-1946 and housed at the Bernard Price Institute of Johannesburg. This new medium-sized basal sauropodomorph, apparently recovered from a multi-specimen bone bed is represented by parts of the postcranial skeleton of at least three individuals, including cervical, dorsal, and caudal vertebrae; most of the forelimb, and part of the hindlimb. We hypothesize that three autapomorphies distinguish BP/1/386 from other basal sauropodomorphs, including: distal carpal I with proximally pointing tip on the palmar margin of its proximal surface, giving a triangular shape in palmar view, a strongly distally tapering craniomedial process of the ulna that is twice as long as the craniolateral process, and a trirradiate ascending process of the astragalus. The inclusion of BP/1/386 in a phylogenetic analysis places it within the group of sauropodomorphs more closely related to sauropods than to Massospondylus (i.e., Sauropodiformes), increasing the currently known diversity of the so-called ?transitional forms? leading to Sauropoda. Character mapping reveals the presence of several features that are common for taxa placed within the transitional branches basal to Sauropoda and in this regard, BP/1/386 and other recently described non-sauropod sauropododiforms, are interpreted as ?transitional? taxa that shed light on the origins of Sauropoda. These characters include: proximal width of first metacarpal more than 100% of its length, presence of a biceps tubercle and caudodistal tubercle of the radius, and strongly concave medial margin of metacarpal I. BP/1/386, together with the remaining transitional forms reported during the last decade, highlights the importance of Gondwanan taxa for the diversity and global record of the group and also for the evolutionary stages of the group related to the rise of sauropods.