First "amphilestid" triconodont from Patagonia, Argentina

GAETANO, LEANDRO C.; ROUGIER, GUILLERMO W.

San Juan

Congreso; Actas IV Congreso Latinoamericano de Paleontología de Vertebrados; 2011

We report here on the first amphilestid triconodont from South America. The specimen (MPEF-PV 2365), an isolated left lower molariform, representing a new taxon, was found in the Jurassic Cañadón Asfalto Fm. at Queso Rallado locality, Cerro Cóndor area, Chubut Province, Argentina. Among mammals, this locality has also yielded an alticonodontine triconodontid, two australosphenidans, and an unpublished allotherian (Gaetano and Rougier, 2011). MPEF-PV2365 is characterized by the presence of a compressed lower molariform bearing five mesiodistally aligned cusps (a-e) with the enamel cover thicker lingually than labially. The main cusp (a) is dominant, centered on the crown, and slightly recumbent. Cusp b and c are mesially and distally pointing, respectively. Tendagurodon janenschi Heinrich 1998, an amphilestid from the Late Jurassic of Tanzania, is the most morphologically similar form to MPEF-PV2365, a fact that is reflected in the results of our preliminary phylogenetic analysis that show these taxa as sister-groups. They share the presence of labiolingually compressed molariforms lacking any dental interlocking structure mesially, crowns longer than tall bearing five cusps mesiodistally aligned, cusp c taller than b, and the mesial margin of cusp a shallowly notched. MPEF-PV2365 is only distantly related to Argentoconodon fariasorum Rougier, Garrido, Gaetano, Puerta, Corbitt and Novacek 2007, the other triconodont known from Cañadón Asfalto Fm. Although similar in size, they differ greatly in molariform morphology. The teeth of Argentoconodon are tall, thin, and trenchant, suggesting a specialized faunivorous/ictivorous habit; the new triconodont (MPEF-PV2365) has the blunter and rounder cusps of a generalist. Amphilestid triconodonts are a wide array of stem-cladotherians that flourished from the Middle Jurassic to the Late Cretaceous (see Kielan-Jaworowska et al., 2004 for a review; Rougier et al., 2007; Gao et al., 2010; Lopatin et al., 2010). They are well represented in northern landmasses while scarce in southern continents. The inclusion of MPEF-PV2365 among amphilestids, and its early age, points to the origin and diversification of these forms under a Pangeic continental configuration at least by Jurassic times.