TESTING HYPOTHESES OF DIFFERENTIAL MAMMALIAN EXTINCTIONS SUBSEQUENT TO THE GREAT AMERICAN BIOTIC INTERCHANGE

A predominant viewpoint on the dynamics of the Plio-Pleistocene exchan ge of mammalian taxa between the Americas invokes competitive displace ment, i.e., the notion that North American stocks outcompeted their So uth American counterparts by virtue of greater resilience to extinctio n and higher rates of colonization and diversification, A recent stati stical test (Lessa and Farina, 1996) based on South American late Plei stocene mammalian genera failed to demonstrate any significant differe nces in extinction rates between South and North American stocks, but showed that body mass was the primary factor statistically associated with the probability of extinction. Here, we provide additional tests of differential extinction in relation to body mass, origin, and troph ic niche, using data of North American late Pleistocene mammals, alone and combined with those of the previous study. Tests were carried out using genera as units and, when possible, also at the species level. The overall results corroborate the notion that body mass is the only factor to show a strong association with the probability of extinction , although there was an additional weak association with trophic niche . (C) 1997 Elsevier Science B.V.