Relative abundances and palaeoecology of four suid genera in the Turkana Basin, Kenya, during the late Miocene to Pleistocene

Abstract

Most suids (Mammalia: Suidae, pigs) worldwide are omnivores living in closed environments, but the African warthog (Phacochoerus) has special adaptations for grazing in open environments. Similar specializations have been recorded from Plio-Pleistocene African suids. Four genera, Nyanzachoerus, Notochoerus, Kolpochoerus, and Metridiochoerus, have been discovered in late Miocene to middle Pleistocene locations around the Turkana Basin. We analyse the relative abundances of these four suid genera compared to other mammals, from approximately 8–0.7 Ma. The dataset includes most of the mammal specimens collected from locations around the Kenyan side of the Turkana Basin. Species of genus Nyanzachoerus were dominant before 4 Ma, but their relative abundance decreases through time thereafter. At the same time, Notochoerus increases in relative abundance, followed by Kolpochoerus, and finally Metridiochoerus. Their peak relative abundances do not overlap: Notochoerus peaks at 3.44–2.53 Ma, Kolpochoerus at 2.53–1.87 Ma, and Metridiochoerus at 1.38–0.7 Ma. We interpret the palaeoecology of these suids based on their relative abundances over time and on published isotope and pollen data. We find that Nyanzachoerus was replaced by its abrasive-diet-specialized successor Notochoerus, possibly in response to a rapid decrease in forest cover. Notochoerus adapted at first to the expanding wood- and grasslands, and then to more arid shrublands. After a period of severe aridity around 2.7–2.5 Ma, more variable environments allowed Kolpochoerus and Metridiochoerus to disperse, while Notochoerus disappeared, perhaps having lost its competitive edge. Further changes in the environment encouraged the expansion of grasslands over shrublands, favouring Metridiochoerus. Kolpochoerus persisted in the more closed environments near water sources.