Miosengi butleri, gen. et sp. nov., (Macroscelidea) from the Kalodirr Member, Lothidok Formation, Early Miocene of Kenya

The only described taxa of early Miocene macroscelideans (afrotherians previously referred to as elephant-shrews, but better dubbed sengis to clearly distinguish them from the unrelated Soricidae or true shrews) are Myohyrax oswaldi from the Kenyan sites of Karungu, Chamtwara and Songhor, and Arrisdrift in Namibia (Senut 2003), Protypotheroides beetzi also from Namibia, Miorhynchocyon spp. from a large number of localities in Kenya, and Hiwegicyon juvenalis from Rusinga Island in Kenya (Butler, 1984, 1995). The first three taxa respectively represent the macroscelidid subfamilies Myohyracinae (Myohyrax and Protypotheroides) and Rhynchocyoninae (Miorhynchocyon), while Hiwegicyon (a taxon only known from a juvenile specimen) is of unknown affinities. The Macroscelidinae, the subfamily that comprises most living sengis, is a ghost lineage through this time interval. Older representatives of the Neogene subfamilies are unknown, although macroscelideans noted from the late Oligocene of the Rukwa Rift Basin in Tanzania may relate to those of the Neogene (Stevens et al., 2006; Stevens et al., 2008). The first appearance of macroscelidines is the middle Miocene locality of Fort Ternan (Butler, 1984, 1995), where Pronasalio ternanensis occurs at approximately 13.7 Ma (Pickford et al., 2006). However, the split of macroscelidines from other sengi lineages has been hypothesized to occur by the beginning of the early Miocene, based on the presence by this time of its putative sister lineages the Myohyracinae and Rhynchocyoninae. Additionally, some molecular phylogenies suggest rhynchocyonines had split off in the Eocene to early Oligocene (42.7 4.8 Ma) and the presence of divisions within the Macroscelidinae such that the group comprising the extant Petrodromus, “Elephantulus” rozeti, and their sister taxon Macroscelides diverged from the group containing other species of Elephantulus in the late Oligocene to early Miocene (21.3 3.3 Ma) (Douady et al., 2003). Thus, particularly given the potential discrepancies of molecular clocks, early Miocene representatives of Macroscelidinae are crucial to better understanding the evolution of the group. Here we describe the first record of an early Miocene macroscelidine sengi that helps fill this gap in the subfamily’s fossil record and provides insights into the morphological diversification of the group. The new taxon is from the locality of Kalodirr, located in northern Kenya about 30 kilometers west of the shore of Lake Turkana and a few kilometers north of the road leading from Lodwar to Kalakol (Fig. 1). A team from the National Museums of Kenya led by Richard and Meave Leakey conducted several field seasons at the site between 1983 and 1987. They recovered a diverse mammalian fauna with a significant small mammal component. The site is best known for its three primate genera; Afropithecus turkanensis, Turkanapithecus kalakolensis, and Simiolus enjiessi (Leakey and Leakey, 1986a, b; Leakey and Leakey, 1987). Although the primates have been the subject of several studies (Leakey and Walker, 1997; 1988a; Leakey et al., 1988b; Patel and Grossman, 2006; Rose et al., 1992), the rest of the fauna is only now being formally described (Grossman, unpubl. data). The new taxon represents the earliest known member of the subfamily Macroscelidinae and is the only macroscelidean known from the fauna. Geological Setting and Age of the Fossils—the site of Kalodirr (“Oryx” in the Turkana language) is located at the headwater of the Kalodirr River (3 20’N, 35 45’E) between the Lokipenata Ridge and the Basalt Hills to the east (Boschetto et al. 1992; Leakey and Leakey 1986a, b). The fossils were recovered from sediments within the latest early Miocene Kalodirr Member of the Lothidok Formation (Boschetto, 1988; Boschetto et al., 1992). The age of the Kalodirr fauna can be well constrained based on K/Ar dating of the underlying Kalodirr tuffs (17.5 10.2 Ma) and the overlying Naserte tuffs (16.8 0.2 Ma), which divide the Kalodirr Member from the younger Naserte Member of the Lothidok Formation. The Miosengi fossils were found during sieving and their exact location within the member is unknown Sedimentological analyses indicate deposition via small meandering stream channels (Boschetto, 1992). Environmental reconstructions for the sites of Kalodirr and Moruorot based on the mammalian fauna indicate that the site was probably a closed to open woodland habitat (Grossman 2008a, b). This interpretation is further supported by plant fossils from the site; these include broad leaved forms, some possessing an acuminate tip ("drip tip") indicating seasonally wet conditions (Boschetto, 1992). Additionally, a number of fish, a pelomedusid turtle, and crocodilian fossils also indicate the presence of lacustrine or fluvial water. Institutional Abbreviations—KNM, Kenyan National Museums, Nairobi, Kenya; KNM-WK, KNM specimens from the site of Kalodirr, Kenya; KNM-FT, KNM specimens from the site of Fort Ternan, Kenya; MVZ, Museum of Vertebrate Zoology, University of California, Berkeley, California;UCMP, University of California Museum of Paleontology, Berkeley, California.