Evolving climates and mammal faunas in Cenozoic South America

PASCUAL, ROSENDO; ORTIZ JAUREGUIZAR, EDGARDO

JOURNAL OF HUMAN EVOLUTION

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 1990 vol. 19 p. 23 - 60

0047-2484

A multivariate analysis of the current South American Land-Mammal Ages is used to reanalyse the recognized "faunistic (mammal) units" or chronofaunae that appear related to radical environmental and climatic changes, which we characterize as Faunistic Cycles and Subcycles. The compositional changes recorded in the successive Faunistic Cycles reflect regional environmental and climatic variations, thus patterns of climatic change. Basically we used cheek teeth of ungulates"natives and immigrants" as an indicator of dietary preference. We then try to infer the structure of successive fossil ungulate communities to deduce the structure of their associated vegetation, and thus the prevailing climatic conditions. We also used other native mammals that followed similar dental modifications, e.g., some rodents and some marsupials, and various types of biological and/or geological evidence. These include climate-sensitive or ecologically specific animals or plants, changes of regional distribution and lithological features of the mammal-bearing formations, diastrophic events, changes in global marine temperatures, and sea-level changes, to contrast those climatic and environmental inferences.We conclude that: (1) From the oldest to the youngest cycles the ungulates changed from browser sylvan types to predominantly open country and grazer types as warm, humid sylvan environments became drier and more temperate. (2) The earliest mammal communities (Paleocene-Eocene), excluding the peculiar Cochabambian Cycle, show a higher diversity but are composed of taxa with less extreme morphological differences. Even mammals placed in different orders were not nearly as dissimilar as their later counterparts. This relationship gradually became reversed within the later communities, i.e., lower diversity but taxa with more extreme morphological differences; that is, mammals placed in separate orders became more divergent. (3) According to the record of mammals as well as other climate-sensitive organisms, warm and relatively humid forested environments had a wider latitudinal range, stretching at the very least to the northern part of the Antarctic Peninsula. (4) With some regional range fluctuations, Paleogene and Early Miocene tropical to subtropical environments remained very well represented as far as the southern tip of the continent. (5) The Middle Miocene mammals (beginning of the Panaraucanian Faunistic Cycle) indicate that favorable environments were shifted to northern Patagonia and that many climate-sensitive mammals (including platyrrhine monkeys) disappeared from Patagonia, in correlation with the waning or extinction of many taxa related to subtropical woodlands. (6) Mammals of the Panaraucanian Cycle and the Pampian Subcycle clearly indicate that this was the time of the most extensive open-country environments, progressively ranging from wetter subtropical savannas to cold-temperate steppe-like habitats. Most of the mammals of this time were savanna-adapted or steppe-adapted elements. (7) Mammals representing the Postpampian Subcycle attest to the wide swings and cyclicity of the Cenozoic climates. (8) According to the Brazilian mammal records, as well as other biological evidence from the isthmian region, the rainy forested areas characterizing those regions evolved quite recently, by the latest Pleistocene to Recent times.