EL BIPEDISMO DE LOS MEGATERIOIDEOS ESTUDIO DE PISADAS FOSILES EN LA FORMACION RIO NEGRO TIPICA

Abstract

Two long sections of (probably) a unique trackway, discovered in the sandstones of the Río Negro Formation, in the vicinity of Carmen de Patagones town, homonymous District, Province of Buenos Aires, are studied. The main interest of the find is the fact that the trackway has been printed by an enormous biped mammal, whose foot's Ienght is estimated in 65 cm average. From the biomorphologic and biostratigraphic analysis it is deduced that this was a Megatherioidea, close to Megatheridium and other Pliocene genera; it is named Megatherichnum oportoi. lts gait and biped actitude patterns are then analyzed. Finally, the last chapter is devoted by the author to the problem of the Río Negro Formation's age -accepted to be Meso- to Neopliocene- and a discussion on the ecological conditions of its deposition. Concerning this point, he argues that the primigenial Negro river's course was already shaped, while the clima tic oscillating conditions anticipated those of the Quaternary .