MIOCENE BEAKED WHALE FROM WEST TURKANA, KENYA, AND PALEOELEVATION OF THE NORTHERN KENYA RIFT

Ziphiid whales are deep diving odontocetes, which occasionally enter rivers, such as the 2006 example of the Thames whale (Hyperoodon ampullatus). Their fossil record in Africa derives mainly from specimens dredged off the South African coast, with the notable exception of a skull fragment discovered by the 1964 Harvard expedition to Loperot, West Turkana, Kenya. We present a phylogenetic analysis of the Kenya ziphiid and discuss its relevance to paleoelevation of the Northern Kenya Rift. The Kenyan ziphiid was discovered in strata equivalent to the Kalodirr and Naserte Members of the Lothidok Formation, along with freshwater mollusks, fish, turtles, crocodilians, and terrestrial mammals, at an elevation of some 600 m and approximately 700 km inland, below a basalt dated at 17.1 ± 1.0 Ma (K/Ar). The Early Miocene Loperot mammalian fauna is most similar to that of Kalodirr, which includes the primates Turkanapithecus and Afropithecus. Because of the presence of the ziphiid, the associated fauna must have lived near sea level, which was approximately similar to that of the current day. The most likely route for stranding was through a drainage controlled by a remnant of the Cretaceous Anza Rift. Net uplift of Loperot to its current elevation thus began after 17 Ma, either driven by large-scale interactions between a mantle plume with the surface at that time or through local flank uplift of the Turkana Rift during the Pliocene. On the eastern flank of the Kenya Rift, lava flow modeling of the 13.5 Ma Yatta phonolites indicates that the elevation from which the Yatta flow originated was up to 1400 m. Loperot need not have the same elevation history as the Yatta phonolitic flow; however, these are the only two empirical paleoaltitude estimates available for the entire region and they are in relatively close proximity, so a temporal and spatial topographic correlation between both sites seems legitimate. The Kenya ziphiid demonstrates that the paleoaltitude of Loperot was near sea level and had a connection with the Indian Ocean some 3 to 4 million years prior to the emplacement of the Yatta phonolites.