Origins, early radiations, and distribution of south american mammals: from greenhouse to icehouse worlds

GOIN, F.J.; GELFO, J. N.; CHORNOGUBSKY, L.

Mendoza

Congreso; International Mammalogical Congress; 2009

SAREM

Two major factors preclude a better understanding of the evolution of mammals in South America: first, the still extremely scarce Mesozoic fossil record; second, the fact that most of the Mesozoic, and very much of the Cenozoic, mammalian fossils are known from a single region: Patagonia. This region, as well as part of the Andean Range, is better understood in biogeographical terms as part of the Austral Kingdom, distinct from the Neotropical Region (Holotropical Kingdom); the former can be traced back deeply into Mesozoic times. At least five successive phases in South American mammalian evolution can be envisaged, being the oldest one largely hypothetical: (1) Early Gondwanian (?late Triassic-early Cretaceous): its mammals are of Pangeic (triconodontids with amphilestid affinities) and Gondwanian origins (autralosphenids). (2) Late Gondwanian (late Cretaceousmedial Paleocene): strong endemism in most lineages of Pangeic (Dryolestida) and Gondwanian (Gondwanatheria) origins, and first records of therians. (3) Early South American (late Paleocene-latest Eocene): strong radiations within Metatheria and Eutheria. (4) Late South American (early Oligocene-late Miocene): standardization of relatively few lineages among metatherians, strong radiation of hypsodont types among South American native «ungulates». Finally (5) Interamerican (late Miocene-Recent): mixture of North and South American therian lineages, progressive decline of native faunas. Among the biotic and abiotic events that triggered these phases there are: the last global warming event at the beginning of the late Cretaceous (between phases 1 and 2); an intermittent bridge between North and South America by the late Cretaceous, favoring the First American Biotic Interchange (FABI), and the K-T extinction event (between 2 and 3); global cooling and full widening of the Circumpolar Antarctic Current, and arrival of platyrrhines and caviomorphs (between 3 and 4), and the beginning of the Great American Biotic Interchange (GABI) and full influence of the Andean uplift (between 4 and 5).