FOSSIL-BASED DATING OF THE DIVERGENCE OF HOMINOIDEA AND CERCOPITHECOIDEA

Living Catarrhine primates comprise the sister groups Hominoidea (apes) and Cercopithecoidea (Old World monkeys). Molecular estimates of the time of the hominoid-cercopithecoid divergence generally fall in the early Oligocene, with six recent studies finding ages between 29.3 and 32.1 Ma (mean 30.8 Ma). These ages substantially predate the oldest known hominoid and cercopithecoid fossils, which are dated at 25.2 Ma. However, due to incomplete fossil preservation, the earliest fossil occurrences invariably underestimate the true divergence date. Here we estimate the age of the hominoid-cercopithecoid divergence using only the fossil record. Using the PBDB and primary literature, we compiled a database of hominoid and cercopithecoid fossils from the Middle Miocene and earlier, comprising 63 fossil occurrences. We then used a new statistical method, the Adaptive Beta method, which is able to calculate confidence intervals on stratigraphic ranges without assuming uniform fossil recovery potential. We applied the Adaptive Beta method to our dataset to estimate the age of the earliest member of the combined group (Hominoidea + Cercopithecoidea), which is equivalent to estimating their date of divergence. The resulting estimate of 30.5 Ma is identical to the mean of six recent molecular studies. Thus molecular-based divergence ages can concur with fossil-based ages if one accounts for the incompleteness of the fossil record. However, when there is disagreement, both sources of evidence are open to question.