EXPLORING EARLY MIOCENE AFRICAN CATARRHINE EVOLUTION THROUGH PALEOENVIRONMENTAL RECONSTRUCTION; LOPEROT, KENYA

Hominoid apes and cercopithecoid monkeys diverged from a common ancestor during the Late Oligocene-Early Miocene. However, despite their abundance in Africa during this time, ape and monkey fossils are only sometimes found together at the same site. Paleoenvironmental reconstructions of Early Miocene catarrhine sites can provide important information about the forces that shaped the composition of these communities and the evolution of modern catarrhines. Unfortunately, in-depth paleoenvironmental data are lacking for many catarrhine-bearing Early Miocene sites, making comparisons among sites difficult. Loperot is an Early Miocene site in West Turkana in Kenya with a unique catarrhine community, and is an important site lacking such detailed analysis. This project aims to reconstruct the paleoenvironment of Loperot using sedimentology and palynology in order to illuminate the extent to which paleoenvironment affects the geographic distribution of Miocene primates.

The catarrhine community of Loperot combines two apes (Rangwapithecus gordoni and Limnopithecus legetet) and a monkey (Noropithecus sp.), each previously known from different regions and never found together. The mammal community includes numerous taxa of all size ranges from proboscideans to rodents-- an assemblage that indicates an Early Miocene age but provides less specific evidence about paleoecology. Given the presence of apes and tragulids, our working hypothesis is that Loperot was a closed-canopy forest.

The fossils are concentrated in quartz sands interbedded with red silts. The sands are immature, cross-bedded, and contain freshwater oysters and crocodile remains, indicating a perennial river system. The red silts exhibit peds, contain rhizoliths and gypsum, and are interpreted as paleosols. The interbedded nature of these units suggests a dynamic landscape. Pollen analysis reveals an abundance of grass and herbs, indicating a more open, riparian type forest rather than a closed canopy.

While this interpretation was unexpected, our data highlight the diversity of environments occupied by Early Miocene catarrhines. This study provides important information about early catarrhine paleocommunities and has important implications for catarrhine evolution, biogeography, and paleoecology.