Metatarsals from the upper cretaceous from Mendoza, Argentina

ALEXIS M. ARANCIAGA ROLANDO; BRISSÓN EGLI F.; SEBASTIAN ROZADILLA; FERNANDO E. NOVAS

Diamante

Jornada; XXIX Jornadas Argentinas de Paleontología de Vertebrados; 2015

Comision organizadora de las XXIX Jornadas Argentinas de Paleontología de Vertebrados

Megaraptorans are clade of medium to large sized predators currently known from Cretaceous strata from South America, Australia and Asia. The systematic position of the group has been hotly debated. Here we describe isolated metatarsals (MCNA-PV-3138) assignable to Megaraptoridae coming from the Anacleto Formation, Neuquén Group (Santonian, Late Cretaceous) at Cañadon Amarillo locality. The material consists on a left incomplete foot. Metatarsals are long and slender. Metarsal II shows its proximal end lateraly compressed and its medial surface is flat for the articulation with metatarsal III. Its distal end is assymetrical with the medial ring larger than the lateral one. Metatarsal III shows it proximal end strongly anteroposteriorly expanded and fan-shaped in lateral view. On its posterior proximal half there is a lateraly projected flange that contacted metatarsal IV. The distal end has a deep flexor pit crescent-shaped in contour and with well-defined margins. Metatarsal IV is the shortest metatarsal. It is proximaly thick, and is strongly transversely expanded on its posterior margin. The proximal medial surface shows a well developed concavity to receive the lateral projection of the third metatarsal. The distal end shows strongly asymmetrical distal condyles, with the lateral much larger than the medial. Detailed comparisons with other theropods reveal a series of new characters that emerge as diagnostic of Megaraptoridae: 1) metatarsal IV very robust, with strongly asymmetrical distal end, 2) lateral flange on proximal end of metatarsal III, and 3) metatarsal IV with proximomedial concavity for contacting the proximal flange of metatarsal III.