New specimens and phylogenetic relationships of the South American Jurassic triconodont Argentoconodon fariasorum

GAETANO, LEANDRO C.; ROUGIER, GUILLERMO W.

Pittsburgh

Congreso; Seventieth Annual Meeting Society of Vertebrate Paleontology; 2010

Osteological remains of Jurassic mammaliamorphs in South America are only known from the Queso Rallado locality, in central Chubut Province, Argentina. The Jurassic deposits of the basin include the Lonco Trapial and Cañadon Asfalto formations that likely span the Middle Jurassic. Three different mammaliaform groups are found in this locality: australosphenidans, an undescribed allotherian, and a triconodont. The latter, Argentoconodon fariasorum, was originally described on the basis of an isolated upper molariform; several additional A. fariasorum specimens are now available, including one which preserves upper and lower jaws, as well as many postcranial elements. We reconstruct the dental formula as I?C1P3M3/i?c1p4m3. Argentoconodon´s dentition is very similar to that of Volaticotherium antiquus, likely from the Jurassic of China, and both of them resemble Ichthyoconodon jaworowskorum from the Cretaceous of Morocco. The anatomical similarity between Argentoconodon and Volaticotherium extends to some postcranial elements. A phylogenetic analysis including most recently described triconodonts recovers a clade formed by Argentoconodon, Volaticotherium and Ichthyoconodon, with a minimal mid-Jurassic age and a wide, likely Pangeic, distribution. This clade is nested within the traditional subfamily Alticonodontinae among triconodontids, supporting Volaticotherium as a triconodontid and not as a representative of a major new clade distantly related to other triconodonts as originally reported. Postcranial similarities between Argentoconodon and Volaticotherium suggest they may have had similar locomotory habits; thus, if Volaticotherium was a glider, Argentoconodon was likely, too.