Velocisaurids in South America and Madagascar

FEDERICO L. AGNOLÍN; FERNANDO E. NOVAS; SEBASTIÁN APESTEGUÍA

Santa Rosa, La Pampa

Jornada; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentinca y simposio de Tafonomía y Paleoecología; 2003

Universidad Nacional de La Pampa

The family Velocisauridae was created by Bonaparte to include the bizarre Velocisaurus unicus Bonaparte, from the Santonian Bajo de La Carpa Formation, early recognized as an indeterminate ceratosaurian. Velocisaurus can be included within Abelisauroidea for having the ginglimoid of the third metatarsal very low, a strongly irregular distal trochleae of fourth metatarsal, with the external condyle reduced and the internal one distally projected, the second metatarsal with a strongly compressed area placed proximal to the distal trochleae, and the characteristic pedal ungueal structure described by Novas and Bandyopadhyay. Recently, the small-bodied abelisauroid Masiakasaurus knopfleri Sampson, Carrano & Forster, was discovered in Maastrichtian outcrops of Madagascar. Velocisaurus and Masiakasaurus share slender metatarsals II and IV, and very gracile and non-raptorial pedal phalanges with a long dorsal process. This features, which distinguish them from other abelisauroids, prompts the inclusion of the latter within Velocisauridae. Additionally, a reduced and thin 2nd metatarsal, suggest close relationships with the noasaurid Noasaurus leali Bonaparte y Powell. However, noasaurids differ from velocisaurids in having a specialized raptorial ungueal structure. The Velocisauridae and the Noasauridae form a monophyletic clade of small-bodied abelisauroids that would also include forms from the Cenomanian of Egypt and Aptian of Brazil. The extremely symmetrical pes of the abelisauroids, with a wide third metatarsal and strongly compressed lateral metatarsals, resemble running birds (e.g. Rhea), suggesting cursorial capabilities. The recognition of velocisaurid abelisauroids both in Patagonia and Madagascar adds a new major component to the Gondwanan Late Cretaceous fauna, increasing their diversity and thus suggetsing an endemic origin for the Abelisauroidea.