The Anthracotheriidae (Mammalia, Artiodactyla) from the middle Miocene Aka Aiteputh Formation in Nachola, northern Kenya

We review the Anthracotheriidae (Mammalia, Artiodactyla) from the lower part (ca. 15.0–14.4 Ma) of the middle Miocene Aka Aiteputh Formation in Nachola (northern Kenya), with a description of the specimens. The anthracotheriids of the Aka Aiteputh Formation in Nachola consist of two bothriodontine species, Brachyodus aequatorialis nacholaensis subsp. nov. and Nacholameryx baragoiensis gen. et sp. nov. The materials of B. aequatorialis nacholaensis consist of gnatho-dental, phalanx, metapodial, and scaphoid specimens that likely comprise a single individual. B. aequatorialis nacholaensis is distinguished from Brachyodus aequatorialis aequatorialis in having a lingual postprotocrista on P4 and a better developed cuspid on the p4 talonid and in lacking a buccal postprotocristid on p4. The materials of N. baragoiensis consist mainly of isolated teeth. N. baragoiensis is characterized by relatively small body size, tetracuspidate upper molars with a looplike mesostyle and without a lingual postprotocrista, lower molars with a preprotocristid and prehypocristid (cristid obliqua) reaching close to the lingual margin of the crown, a buccally positioned m3 hypoconulid, and a better-developed and isolated paraconid and metaconid (or entostylid) on p4 with an extra cuspid between the protoconid and the paraconid. Our phylogenetic analyses recover Nacholameryx as the sister taxon of the [Merycopotamus + Libycosaurus] clade within the Merycopotamini, raising the possibility that the [Merycopotamus + Libycosaurus] clade originated in Africa during the middle Miocene. This revision of the Nachola anthracotheriids demonstrates that the results of previous faunal analyses of the Nachola mammals should be reappraised.