Abstract
The available fossil record indicates that primates have occurred in South America since the middle Tertiary. The oldest known primate-bearing locality, Salla, Bolivia, of Deseadan age, was previously thought to be about 35 myr old, or early Oligocene age. However, 12 radioisotopic dates from Salla using 40 K- 40 Ar and fission-track methods and magnetostratigraphic correlations indicate a late Oligocene age for this site. The exact level that produced the earliest-known South American primate, Branisella , lies just above a tuffaceous zone that yielded dates of 26·4 ± 1·0 and 25·1 ± 0·7 Ma. The revision of the “primate datum” in Bolivia from early to late Oligocene has ramifications for: (1) the calibration of other, younger primate-bearing localities in South America; and (2) biogeographic hypotheses concerning primate origins in light of plate tectonics. The other known Tertiary primate localities in South America are of Colhuehuapian (ca. 18–19 Ma). Santacrucian (ca. 15–18 Ma) and possible Friasian (ca. 14–15 Ma) ages. There is a major gap of some 14 myr that exists between these primate occurrences of middle Miocene age and the next younger localities, which are all late Pleistocene.
Published Version
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