MONKEYS AND APES LIVING TOGETHER? A PALEOENVIRONMENTAL RECONSTRUCTION OF LOPEROT, A MIOCENE PRIMATE SITE IN WESTERN TURKANA

Hominoid apes and cercopithecoid monkeys split from a common ancestor during the Late Oligocene and proliferated during the Early Miocene. During this time, apes and monkeys are only sometimes found together within a site, but when and where this should occur is difficult to predict. While geologic age and geography certainly play a role in community structure, paleoenvironment likely played a significant role in shaping Early Miocene catarrhine communities. Here, we reconstruct the paleoenvironment of the Early Miocene site of Loperot in West Turkana in Kenya. The faunal assemblage at Loperot preserves apes and a monkey enabling assessment of the extent to which paleoenvironment may affect the geographic distribution of primates during this critical time in their evolution in Africa. Loperot preserves a unique catarrhine community, combining two apes (Rangwapithecus gordoni and Limnopithecus legetet) and a monkey (Noropithecus sp.), each previously known from different regions but previously not found together. The faunal assemblage and stratigraphy at Loperot indicate an Early Miocene age but paleoenvironmental reconstructions using only fauna are inconclusive. Other similar-aged ape sites (i.e., Rusinga and Songhor) are reconstructed to be multi-story closed-canopy forests. At Loperot, climbing ripples, scour-and-fill structures, and fining-up sequences represent fluvial sands, and preserved aquatic fauna and flora suggest a perennial river system (e.g., remains of a ziphiid whale indicate a large fluvial conduit between Loperot and the Indian Ocean). Smectitic paleosols (vertisols) intercalated with the fluvial sands contain zeolites and gypsum, suggesting formation in an arid to semi-arid climate. Palynology reveals an abundance of grass and herb species and a lack of ferns, forcing a reevaluation of the closed-canopy hypothesis. We, therefore, reconstruct the paleoenvironment of Loperot as a riparian gallery forest that was part of a more open landscape, making Loperot unique amongst other Early Miocene primate sites and indicating that Miocene apes could occupy a greater diversity of habitats that previously suggested.