MIOCENE MAMMALS, STRATIGRAPHY AND ENVIRONMENT OF MURUAROT HILL, KENYA BY CARY T. MADDEN ABSTRACT Fossil mammals from Muruarot Hill in northwestern Kenya are conspecific with mammals in the Early Miocene fauna of Rusinga Island indicating that the age of the Muruarot Hill fauna, long disputed, is almost certainly Early Miocene. Analyses of the sediments and the gastropod and mammal faunal indicates that the paleoenvironment of the site was probably semi-arid and relatively open with shallow, swampy lakes. INTRODUCTION Miocene mammals were first described from Muruarot Hill, near Lodwar, in northwestern Kenya (Fig. 1) by the French paleontologist Camille Arambourg (1933). Arambourg compared nearly all of his fossils with similar mammals from the Burdigalian of Europe and concluded that they were more primitive, and therefore, somewhat older than their closely related European counterparts. He consequently placed his fauna in the earliest Burdigalian which was then usually considered to be the earliest subdivision of the Miocene Epoch (Davies, 1934). Since the time of Arambourg's report, fossil mammals have been recorded from Muruarot Hill by several workers (Deraniyagala, 1951; Whitworth, 1954, 1958; Savage, 1965; Hooijer, 1968; Churcher, 1970). Although most of the taxa recorded by these workers are generally considered to be characteristic of an Early Miocene age (see Table 1), and they thus tended to substantiate Arambourg's relative age determination, the age of the Muruarot fauna has nonetheless been disputed (see, for example: Deraniyagala, 1948, 1951, 1955; Patterson, in: Reilly et al., 1966; Bishop, 1967; Leakey, in: Bishop, 1967; Walsh and Dodson, 1969). In March and April, 1948, a field party from the University of California African Expedition, led by H.B.S. Cooke, collected over 300 specimens of fossil mammals from deposits at Muruarot Hill. Until now, only one specimen, the skull of the rhinoceros Aceratherium acutirostratum (Deraniyagala), has been described from this large collection, almost all of which is presently conserved in the University of California Museum of Paleontology (UCMP), Berkeley. The new faunal components recorded in this paper, as well as those recorded by previous workers, support Arambourg's assignment of the Muruarot Hill fauna to the Early Miocene. 1 TABLE 1 FOSSIL MAMMALS PREVIOUSLY RECORDED FROM MURUAROT, WITH TAXONOMIC REVISIONS ORIGINAL REVISION Hyaenodon andrewsi Savage Kichechia zamanae Savage-*• Mastodon cf. angustidens Cuvier^ 9 Pliohyrax championi Arambourg Turkanatherium acutirostratum Deraniyagala^ Aceratherium acutirostratum (Deraniyagala)4 Aceratherium? sp. Listriodon jeanelli Arambourg^ Suide indetermine^ Brachyodus? sp. Dorcatherium chappuisi Arambourg^ Dorcatlierium pigotti Whitworth-5 Dorcatherium parvum Whitworth^ Palaeomeryx africanus Whitworth Palaeotragus primaevus Churcher" Bovide indetermine PECORA Incertae Sedis (medium and large spp.)5 Gomphotherium angustidens (Cuvier) Megalohyrax championi (Arambourg)8 Aceratherium acutirostratum (Deraniyagala)^ Aceratherium acutirostratum (Deraniyagala) [in part] Aceratherium or Dicerorhinus sp. [in part] Aceratherium or Dicerorhinus sp. Bunolistriodon jeanelli (Arambourg)' Suidae gen. et sp. indet. Brachyodus sp. indet. Propalaeoryx nyanzae Whitworth l^J Palaeotragus ? primaevus Churcher Giraffoidea indet. PECORA indet. (medium and large spp.) 1. Savage (1965) 2. Arambourg (1933) 3. Deraniyagala (1951) 4. Hooijer (1968) 5. Whitworth (1958) 6. Churcher (1970) 7. Arambourg (1947) 8. Whitworth (1954) 9. Arambourg (1959) 10. Hamilton (1971, written communication) 2 GEOGRAPHIC AND STRATIGRAPHIC OCCURRENCE The University of California Museum of Paleontology faunal collection was recovered from two localities. The primary locality is designated Muruarot 2 (UCMP locality V-48100). Although Arambourg stated in his initial report (1933) and in subsequent ones (1943, 1947) that his fossils originated from Losodok, the members of the University of California field party found Arambourg's quarry at Muruarot 2 when they first began excavations in 1948 (Cooke, 1948, in manuscript; University of California African Expedition Field Catalogue; Phillips, 1949). Figure 1. Map showing Muruarot Hill, which is just south of the Lopi River (R. Lopi). The site of Arambourg's fossil quarry is indicated by an "F". Adapted from Arambourg (1933). This site also has yielded most of the fauna recorded by workers subsequent to Arambourg. It is located on the southeast slope of Muruarot Hill, approximately 20 miles N.E. of Lodwar and 12 miles W. of Lake Rudolf, in the Lothidok Hills region of northern Turkana District, northwestern Kenya (03° 15'N, 35° 47'E). The base of the principal fossiliferous stratum is about 1700 feet above sea level, some 90 feet above the present level of Lake Rudolf. The secondary locality, Muruarot 1 (UCMP locality V-4898), is situated on the north face of Muruarot Hill about three-fifths of a mile from the main site. 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