South American Jurassic Mammals: their relationships and paleobiogeographical implications

GAETANO, LEANDRO C.; ROUGIER, GUILLERMO W.

Heidelberg

Congreso; 22nd International Colloquium on Latin American Earth Sciences; 2011

Heidelberg Universität

South American Jurassic mammaliaform corporeal remains have only been reported from Queso Rallado locality, in Chubut Province, Argentina. The bearing strata probably represent the basal levels of the Cañadón Asfalto Fm, which are thought to be of Toarcian age (Cuneo & Bowring, 2010). The mammaliaform fauna found in this locality is composed at present by three described forms: Argentoconodon fariasorum, Asfaltomylos patagonicus, and Henosferus molus. Argentoconodon is closely related to Ichthyoconodon jaworowskorum and Volaticotherium antiquus, forming a clade nested among alticonodontine eutriconodonts. Given this scheme of relationships, Argentoconodon might be the earliest representative of Triconodontidae. Moreover, Ichthyoconodon and Volaticotherium lineages must have been present at least from the Early Jurassic. This also applies to the other members of Alticonodontinae, only reported from North American Cretaceous localities (see Kielan-Jaworowska et al., 2004). Asfaltomylos patagonicus and Henosferus molus have been regarded as basal members of Australosphenida (Rougier et al 2007), extending the temporal range of this group to the Toarcian. Australosphenidans molariforms highly resemble tribosphenic ones; in contrast, Jurassic forms from Northern landmasses lack tribosphenic-like teeth (see Kielan-Jaworowska et al., 2004) except for the enigmatic Shuotherium dongi from the Late Jurassic of China (Chow & Rich, 1982). Jurassic South American mammaliaforms point to the origin of australosphenidans and alticonodontines prior to the complete separation of Southern and Northern landmasses in a Pangeic paleogeographic setting.