The probably origin and separation of the Eremotherium clade (Xenarthra, Megatheriidae)

BRANDONI, D. Y CARLINI, A. A.

Puerto Madryn, Chubut

Jornada; Reunión Anual de la APA; 2005

Recently we describe the first two Tertiary Megatheriinae from Venezuela, which are the second record of the subfamily at low latitudes in Northern South America. One of them was described on skull remains, and assigned to a new genus and species (from the Codore Formation, Pliocene). As we proposed, this species is closely related to Eremotherium Spillmann, and this clade could have evolved at lowlands of middle and low latitudes in Northern South America and Central America. Regarding the relationships among the species of Eremotherium, some authors stated that E. eomigrans De Iuliis and Cartelle and E. laurillardi (Lund) formed a phyletic sequence. Until now, no ancestral forms of Eremotherium are known, and this new Megatheriinae shows many of the expected characters for an ancestor. Likewise, as E. eomigrans and E. laurillardi were proposed as forming a phyletic sequence; this one could have begun with the Venezuelan Pliocene new species. The lineage that culminates in Eremotherium retained more plesiomorphic characters (midline sigmoid shape of the skull, low occipital condyles with respect to the palatal plane, low hypsodonty) than those in taxa related to the origin and diversification of Megatherium Cuvier. On the other hand, Megatherium altiplanicum Saint-André and De Iuliis from the Upper Pliocene of the Bolivian altiplano, represents the oldest record of this temperate genus, while the separation of the genera Eremotherium and Megatherium would very probably have occurred during the Late Miocene- Early Pliocene, or even earlier.