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South America was an island continent for most of the last
80 million years. The highly peculiar land mammals arising from this isolation
have captured the interest of biologists and paleontologists for more than
two centuries. Our research group has discovered numerous highly unexpected
fossil mammal assemblages in volcaniclastic deposits of the Andean Main
Range in central Chile during recent years. One of these assemblages is
significant in clarifying a lengthy gap in the South American fossil record
spanning between approximately 30 and 50 million years before present. This
gap coincides with an interval of fundamental faunal and climatic changes
in South America, as well as with the arrival of two exotic lineages there,
primates and rodents. In addition to several other important first and last
occurences, this assemblage is notable in containing the earliest known
rodents from the continent. The occurrence of these fossils in volcanic
deposits enables the application of various "absolute" geologic dating techniques,
providing a precise calibration for many of the fossil assemblages. Other
Andean assemblages are of considerable interest for: 1) pointing to the
enormous potential for discovery of new fossil mammal faunas in the thick
sequence of volcanic sediments of the central Andean Main Range; 2) providing
the first radioisotopic dates available for various portions of the South
American fossil mammal sequence; 3) demonstrating previously unrecognized
geologic complexity in the region; and 4) producing the oldest well preserved
anthropoid primate skull from the Americas. |
