Chondrichthyans and actinopterygians across the K-Pg boundary in Patagonia, Argentina.

KRIWET, J.; ABERHAN, M; KIESSLING, W.; SCASSO, R.A.; MEDINA, F.A.

Austin, Texas, USA

Congreso; 67 annual meeting Society of Vertebrate Paleontology; 2007

Society of Vertebrate Paleontology

Late Cretaceous and Cenozoic fishes are well known from innumerable marine localities throughout the world but are mainly restricted to the Northern Hemisphere. Conversely, the diversity of Southern Hemisphere Late Cretaceous and Cenozoic fishes is still very incompletely known. Most Late Cretaceous and Cenozoic fish remains from Argentina were described in the 19th century. However, this material is very limited to small outcrops and limited collections. Recent field work in Patagonia providaded an improved pictoure of Late Cretaceous to Paleogene chondrichtyans and actinopterygians in high latitudes , demonstrating important ecologic and biogeographic differences but also similarities to contemporary faunas north of the Equator. The new material comes from the Lefipán Fm. (Maastrictian-Paleocene) which overliesdthe Paso del Sapo Fm (Campanian-Maastirctian) in the Middle Chubut River Valley, and for the Jagüel (Maastrichtian) and Roca (Danian) formations of the Neuqueén Basin providing important insights into faunistic changes across the K-Pg boundary in southern high latitudes. In the Chubut River Vallley the depositional environments changed from a fluvial to tidally influenced estuarine environment in the Paso del Sapo Fm to an open marine environmentt in the lower Lefipán Formation. The K-Pg boundary is located within the Lefipán Fm and is represented by a tide-to wave-dominated deltaic system. In the Neuquén Basin, the position of the K-Pg boundary is constrained to the base of a sandstone layer within a 90-m-think succession of monotonous middle to outer shelf mudstones of the Jagüel Fm. Shallow-marine bioclastic limestones oth the Danian Roca Fm ovelie the Jagüel Fm. The new fish material not only allows some general interpretations of chndrichtyan and actinopterygian assemables acresss the K-Pg boundary (e.g. shifting of lamaniform to batoid dominated selachian faunas) but the occurrence of a characteristic chimeroid remains in the Maastrichtian of Patagonia also supports previous intepretations that the high latitudes of the Southern Hemispherte acts as an origination centre from where subsequent migrations to lower latitudes started.