Mammal and Bird footprints from Rio Negro Formation (late Miocene-early Pliocene), Rio Negro Province, Argentina.

SILVIA A. ARAMAYO; MERCEDES BARROS; SOLEDAD CANDEL; LAURA VECCHI

Trelew, Argentina

Congreso; First International Congress on Ichnology "Ichnia 2004"; 2004

Museo Paleontológico Egidio Feruglio

New tetrapod footprints assigned to mammals and birds were discovered in continental deposits from the Atlantic coast of Rio Grande province, Argentina, representing an addition to earlier findings. The study took place along 30 kms of a marine beach area between Balneario El Cóndor and La Lobería, (Lat 41ºS, Long 62º 30´, 64º 30´ W). In this area abrasion platforms crop out as remnants of eroded high cliffs. The footprints occur on silty clay platforms and on fallen blocks lying at the base of the cliffs. The structures were documented by photographs and plaster casts. The ichnofauna includes footprints assigned to tardigrad xenarthrans (Megatherichnum oportoi Casamiquela and cf. Mylodontidichnum Aramayo and Manera de Bianco) and ungulates, together with remarkable trackway of a digitigrad mammal (a carnivorous marsupial) and an undertrack assigned to a phororhacid bird, among other structures. The stratigraphic succession begins with continental deposits at the base of the section, followed by marine and continental rocks cropping out in the cliff wall. The stratigraphic range of the continental ichnofauna extends from the Late Miocene (trackways on the abrasion platforms) to Early Pliocene (footprints on fallen rocks). The fauna inhabited interdune pools and temporary lagoons, such as is indicated by the associated lacustrine deposits with desiccation mud-cracks.