NUEVOS APORTES AL CONOCIMIENTO DE LA ICNOFAUNA DE TETRÁPODOS DEL TRIÁSICO SUPERIOR DE LOS MENUCOS

Abstract

The Los Menucos ichnofauna from the Río Negro province in Argentina, is at present a unique Triassic track association known from Patagonia. The new footprints described in the present study were collected from the same levels where the original tetrapod ichnites from Casamiquela´s works were exhumed. The track-bearing levels are included in the Los Menucos Complex and correspond to fine-grained tuffaceous sandstones interbedded with tuffaceous mudstones that contain a rich "Dicroidium- type Flora". In the present study new groups of trackmakers, that included footprints assigned to terapsid dicynodonts (Pentasauropus sp. Ellenberger) and putative "lepidosaurs" (Rhynchosauroides Maidwell) were identified. The new specimens described do not include ichnites related to archosaurs (basal archosaurs and/or dinosaurs), which are the dominant component in most known Late Triassic Gondwanan tetrapod faunas. Previous assumptions about the relative abundance and high diversity of small therapsids, probably theriodonts represented by the footprint assemblage are corroborated by the new evidence. This unusual situation, which is supported by the new findings, might be due to the record of an endemic fauna actually dominated by therapsid taxa in northern Patagonia.