Article: Reassessment of extinction patterns among the late Pleistocene mammals of South America
Enrique P. Lessa and Richard A. Fariña
After the formation of the Isthmus of Panama, about 2-5 Ma, a massive interchange between the previously separated mammalian faunas of South and North America took place. Afterwards, during the Late Pleistocene (Lujanian Land Mammal Age)-Holocene transition (less than 10000 years BP), many of the taxa originally present in South America became extinct. Here, we report results of a statistical assessment of the relative importance of factors potentially associated with extinctions. Several factors (namely trophic niche, origin, and body size) were tested for their association with the probability of extinction, but body mass was the only factor found to be significantly correlated with the probability of extinction (P < 0-0001). The reduction in deviance with the inclusion of body mass was 55-7 per cent. The fate of 85-6 per cent, of the 120 Late Pleistocene mammalian genera included in the analyses was in accordance with the predictions of a logistic regression model based only on body mass. Trophic niche and origin were also considered, but turned out not to be statistically significant. We propose that the greater resilience against extinction of North American mammalian contingents played no role in the dynamics of the interchange. Also, the analyses demonstrated that marsupials did not go extinct more than placentals. Mammals of North American origin were successful invaders of the South American subcontinent because of their higher speciation rate, and not because of their lower extinction rates.