Mototaka Saneyoshi

A new Late Miocene great ape from Kenya and its implications for the origins of African great apes and humans

Extant African great apes and humans are thought to have diverged from each other in the Late Miocene. However, few hominoid fossils are known from Africa during this period. Here we describe a new genus of great ape (Nakalipithecus nakayamai gen. et sp. nov.) recently discovered from the early Late Miocene of Nakali, Kenya. The new genus resembles Ouranopithecus macedoniensis (9.6–8.7 Ma, Greece) in size and some features but retains less specialized characters, such as less inflated cusps and better-developed cingula on cheek teeth, and it was recovered from a slightly older age (9.9–9.8 Ma). Although the affinity of Ouranopithecus to the extant African apes and humans has often been inferred, the former is known only from southeastern Europe. The discovery of N. nakayamai in East Africa, therefore, provides new evidence on the origins of African great apes and humans. N. nakayamai could be close to the last common ancestor of the extant African apes and humans. In addition, the associated primate fauna from Nakali shows that hominoids and other non-cercopithecoid catarrhines retained higher diversity into the early Late Miocene in East Africa than previously recognized.

The Entelodontid Artiodactyl Fauna from the Eocene Ergilin Dzo Formation of Mongolia with Comments on Brachyhyops and the Khoer Dzan Locality

Abstract. We review the entelodontid artiodactyl fauna of the upper Eocene Ergilin Dzo Formation in southeastern Mongolia. Also, we describe new specimens of Brachyhyops trofimovi from the Khoer Dzan locality and review the characteristics and Asian distribution of Brachyhyops. The revised entelodontid fauna of the formation consists of three species: Entelodon gobiensis (from the Khoer Dzan and Ergilin Dzo localities), Brachyhyops trofimovi (from the Khoer Dzan locality), and Brachyhyops? sp. (from the Ergilin Dzo locality). The discovery of p4 and M2 of B. trofimovi demonstrates the definitive diagnostic characteristics of this species within the genus: p4 is buccolingually wide and is triangular in occlusal view; it has a well developed and high cusp (= hypoconid?), which is fused to the posterior part of the protoconid; and M2 has a better-developed pericone. In Asia, Brachyhyops is recorded only in the southern part during the middle Eocene and only in the northern part during the late Eocene, implying that the genus originated in the southern part of Asia and subsequently migrated northward, giving rise to northern Asian and North American Brachyhyops.

Climate shift recorded at around 10 Ma in Miocene succession of Samburu Hills, northern Kenya Rift, and its significance

Abstract A significant climate shift around 9.6 Ma has been detected from the Middle to Upper Miocene Aka Aiteputh and Namurungule Formations exposed in the Samburu Hills, northern Kenya. Around 9.6 Ma, changes in sediments are recorded from the red soil-dominated interval of the upper Aka Aiteputh Formation to the lacustrine and deltaic facies of the lower Namurungule Formation, containing open woodland/savanna mammalian fauna. These reveal a shift from a dry climate with seasonal precipitation to a climate with strong seasonality. In particular, an increase in precipitation was recorded by the predominance of lacustrine facies. This shift happened at around the same time as the intensification of the Indian summer monsoon that has been detected in the Himalayas and some of surrounding regions. There are two scenarios that could explain the increased precipitation at the beginning of the deposition of the Namurungule Formation: (1) enhanced moisture transport by the Intertropical Convergence Zone (ITCZ), synchronized with Indian summer monsoon intensification, or (2) intensification of the Indian summer monsoon itself, permitting moisture to penetrate deep into East Africa if the altitude of the rifted area was lower than it is now. Presently, the former is considered to be the more plausible explanation for the climate shift detected in the Samburu Hills.

Fossil Evidence of a Mesonychid Mammal from the Upper Eocene Ergilin Dzo Formation, Mongolia

The upper Eocene Ergilin Dzo Formation of southeastern Mongolia yields many terrestrial vertebrate fossils (e.g. Yanovskaya et al., 1977; Russell and Zhai, 1987; Dashzeveg, 1993). Its mammalian fauna is the type fauna of the Ergilian Asian land mammal ‘age’ (ALMA) (Russell and Zhai, 1987). In the Ergilin Dzo Formation, the Mesonychia (= Acreodi), which are archaic Paleogene carnivorous mammals, were cited in the faunal lists by previous researchers: as Mesonychidae indeterminate by Russell and Zhai (1987); and as Mongolestes hadrodens (Mesonychidae) and Metahapalodectes sp. (Hapalodectidae) by Dashzeveg (1993). However, the existence of the mesonychians in the formation has not been documented yet because they have been

Listriodontine Suid and Tragulid Artiodactyls (Mammalia) from the Upper Miocene Nakali Formation, Kenya

Abstract. Two rare artiodactyl mammals from the basal upper Miocene Nakali Formation (ca. 10 Ma) of central Kenya are described. They are cf. Listriodon sp. (Suidae, Listriodontinae) and Dorcatherium cf. pigotti (Ruminantia, Tragulidae), which are the first discoveries of a listriodontine and a tragulid in the formation. Cf. Listriodon sp. is represented by a talonid of a lower molar that has a strongly lophodont hypolophid. Although this listriodontine material is fragmentary, it is comparable in morphology and size to large and fully lophodont species of the genus Listriodon, such as L. splendens and L. pentapotamiae theobaldi. If the Nakali specimen proves to be phyletically closely related to these two species, it indicates that a highly derived lineage of Listriodon existed in East Africa around 10 Ma, implying a possible migration of this lineage from Europe/Asia to East Africa during the middle or earliest late Miocene. Dorcatherium cf. pigotti is represented by DP4 (or M1) and a mandible with p3–m3, which are comparable in size to those of D. pigotti among the African species of the genus. Although the genus Dorcatherium and species D. pigotti are common taxa in the early to middle Miocene of Africa, they are rarely found in the late Miocene. This is the second record of the genus in the late Miocene of Africa, reinforcing evidence that Dorcatherium existed until the basal late Miocene in East Africa.

Taxonomic revisions on nimravids and small feliforms (Mammalia, Carnivora) from the Upper Eocene of Mongolia

This study reports occurrences of feliform carnivorans from the Upper Eocene Ergilin Dzo Formation and Alag Tsav locality of southeastern Mongolia. Nimravus mongoliensis (Nimravidae) is distinguished from other species in having a deep mandible, a longer p/1–2 and m/2 relative to p/4, and relatively wider P3/. Eofelis sp. (Nimravidae), a genus previously known only from the Oligocene of France is found in the Ergilin Dzo Formation. Alagtsavbaatar indigenus comb. nov. (Alagtsavbaatar gen. nov.; Feliformia) is established for new specimens from the Ergilin Dzo Formation and the previously known Stenoplesictis specimen from the Alag Tsav locality based on its characteristics such as moderately developed buccal cingulid and cingular and accessory cuspids on p/3 − 4, wide m/1 trigonid and double-rooted m/2 with a trenchant talonid. Stenoplesictis simplex from the Ergilin Dzo Formation is revised to Asiavorator gracilis, extending its chronological range back to the Late Eocene. Geographical and chronological distributions and morphological comparisons suggest that the Nimravidae originated by the Middle Eocene in southern East Asia and migrated northward in the Late Eocene, whereas the early small feliforms immigrated to northern East Asia in the Late Eocene and stayed within the middle-to-high-latitude area.