THE HISTORY OF SOUTH AMERICAN LAND MAMMALS: THE SEMINAL CRETACEOUS-PALEOCENE TRANSITION
1998; Asociación Paleontológica Argentina; Volume: 5; Issue: 1 Linguagem: Inglês
ISSN
2469-0228
Autores Tópico(s)Mollusks and Parasites Studies
ResumoAbstract. The last records of Late Cretaceous and early Paleocene (Danian-Selandian) mammals from Patagonia together with those from the early Paleocene of Bolivia, are hard evidence that the whole history of the terrestrial South American mammals followed peculiar evolutionary patterns, very different from those of other regions of the world. We recognize two large episodes, which we call the Gondwanic Stage and the South American Stage. Each results from evolutionary processes which involve genetic isolation, and appear to have been related to the two stages of geographic isolation which happened in the South American continent: as part of the Gondwana supercontinent during most of the Mesozoic, and finally as a discrete and isolated continental unit near the end of the Pliocene. The first one was characterized by communities exclusively composed of no-tribosphenic and pre-tribosphenic mammals. The second one included only tribosphenic mammals (except for one monotremata and one non-tribosphenic from the early Palaeocene, and only from Patagonia). The first stage was a severe isolation from the northern continents which integrated into Laurasia. The second, on the other hand, was characterized by sporadic direct or indirect connections with the Laurasian continents, or with Africa. For this reason, all mammals belonging to this second stage are regional products which, in isolation, derived from extracontinental immigrants. The drastic compositional changes between these stages should have happened between the Campanian and Danian, but we lack records which would allow the recognition of their modus operandi . KEY WORDS. Land-mammals. South America. Cretaceous-Paleocene transition. Resumen. LA HISTORIA DE LOS MAMIFEROS TERRESTRES SUDAMERICANOS: LA SEMINAL TRANSICION CRET ACICO-PALEOCENO. Los ultimos registros de mamiferos del Cretacico Tardio y del Paleoceno temprano (Daniano-Selandiano) de Patagonia, sumados a aquellos del Paleoceno Temprano (Daniano tardio?) de Bolivia, son evidencia concreta de que la historia toda de los mamiferos terrestres sudamericanos siguio patrones evolutivos singulares, y muy distintos a aquellos de otras partes del mundo. Reconocemos dos grandes etapas, que distinguimos como la Etapa Gondwanica y la Etapa Sudamericana. Cada una de ellas resulta de procesos evolutivos sucedidos en aislacion genetica, y aparecen como causalmente relacionadas, respectivamente, a las dos grandes etapas de aislamiento geografico por las que paso lo que devendria el continente sudamericano: como parte del Supercontinente Gondwana durante la mayor parte del Mesozoico, y finalmente como una unidad continental discreta y aislada hasta fines del Plioceno. La primera estuvo caracterizada por comunidades compuestas exclusivamente por mamiferos no-tribosfenicos y pre-tribosfenicos. La segunda, por comunidades compuestas exclusivamente por mamiferos tribosfenicos (salvo un monotremata y otro no-tribosfenico del Paleoceno temprano, y solo de Patagonia). La primera etapa fue de un mas severo aislamiento de los continentes del norte, componentes de Laurasia. La segunda, en cambio, estuvo signada por esporadicas conexiones, directas o indirectas, con los continentes laurasicos, y con Africa. Asi, todos los mamiferos de esta segunda etapa son productos regionales que, en aislacion, derivaron de inmigrantes extracontinentales. Los drasticos cambios composicionales entre una y otra etapa debieron ocurrir entre el Campaniano y el Daniano, aunque carecemos de registros que permitan reconocer su modus operandi . PALABRAS CLAVE. Mamiferos terrestres. Sudamerica. Transicion. Cretacico-Paleoceno.
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