Hideo Nakaya

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.

Late Miocene to Pliocene carbon isotope record of differential diet change among East African herbivores.

Stable isotope and molecular data suggest that C4 grasses first appeared globally in the Oligocene. In East Africa, stable isotope data from pedogenic carbonate and fossil tooth enamel suggest a first appearance between 15–10 Ma and subsequent expansion during the Plio-Pleistocene. The fossil enamel record has the potential to provide detailed information about the rates of dietary adaptation to this new resource among different herbivore lineages. We present carbon isotope data from 452 fossil teeth that record differential rates of diet change from C3 to mixed C3/C4 or C4 diets among East African herbivore families at seven different time periods during the Late Miocene to the Pliocene (9.9–3.2 Ma). Significant amounts of C4 grasses were present in equid diets beginning at 9.9 Ma and in rhinocerotid diets by 9.6 Ma, although there is no isotopic evidence for expansive C4 grasslands in this part of the Late Miocene. Bovids and hippopotamids followed suit with individuals that had C4-dominated (>65%) diets by 7.4 Ma. Suids adopted C4-dominated diets between 6.5 and 4.2 Ma. Gomphotheriids and elephantids had mostly C3-dominated diets through 9.3 Ma, but became dedicated C4 grazers by 6.5 Ma. Deinotheriids and giraffids maintained a predominantly C3 diet throughout the record. The sequence of differential diet change among herbivore lineages provides ecological insight into a key period of hominid evolution and valuable information for future studies that focus on morphological changes associated with diet change.

Plio-Pleistocene terrestrial mammal assemblage from Konso, southern Ethiopia

Abstract Mammalian fossils of the Konso Formation (southwestern Main Ethiopian Rift) derive from stratigraphic intervals dated to between 2.0 Ma and younger than 1.3 Ma. Systematic paleontological collecting resulted in almost 8,000 identifiable mammalian specimens representing 8 orders, 22 families, and more than 68 species including Australopithecus boisei and Homo erectus. Despite geographic proximity to the Turkana Basin (approximately 200 km), aspects of the Konso fauna are distinctive, with its 1.9–1.7 Ma assemblage showing some degree of endemism. Bovids Megalotragus, Parmularius altidens, Parmularius eppsi, Menelikia, and Pelorovis, all common at Turkana and/or Olduvai, are rare or absent at Konso, while Parmularius cf. pandatus, Simatherium, and Notochoerus n. sp. of the Konso assemblages are the youngest known records of these taxa in eastern Africa. The dominant suid of this assemblage is Kolpochoerus majus, a previously poorly known taxon. Subsequent to circa 1.7 Ma, an influx of external elements occurred, possibly related to a general East African trend of climatic drying between 1.8 and 1.6 Ma. The post-1.5 Ma Konso fauna is characterized by apparently immigrant dry grassland adapted bovids, such as Damaliscus niro and Parmularius angusticornis. Metridiochoerus compactus, Metridiochoerus hopwoodi and Metridiochoerus modestus are common in the 1.5 to 1.3 Ma levels at Konso, whereas the latter two suids are rare at Turkana. The post-1.5 Ma Kolpochoerus limnetes/olduvaiensis of Konso is morphologically more conservative than time-equivalent Turkana specimens. The post-1.5 Ma Konso Elephas recki represents an evolutionary grade immediately preceding the fully advanced E. recki recki condition.

The Late Miocene Large Mammal Fauna from the Namurungule Formation, Samburu Hills, Northern Kenya

By the Japan-Kenya Expedition, more than 1145 late Miocene vertebrate fossils were collected from the Namurungule Formation in Samburu Hills, Northern Kenya in 1982. These fossils are assigned to at least 29 taxa of which 21 are mammals, including Hominoid, Tetralophodon, two kinds of Hipparion, Brachypotherium, Kenyapotamus, and Pachytragus. Quantitatively, the taxa of Hipparion are the most predominant. But gomphothere, bovid, rhinocerotid and giraffid fossils are approximately as common as each other at Namurungule. Suids, hippopotamids and carnivores seem to be unifonnly rare as fossils at Samburu. In this paper, 19 taxa of mammals are described and discussed briefly. The Namurungule mammalian fauna is closer in age to Ngorora (c. 11 m.y.) than to Mpesida (7 m.y.) from Kenya, and this fauna is similar to the faunas of Samos and Pikermi (Vallesian). It seems that the abundance of Hipparion, giraffids, rhinocerotids and bovids suggests a woodland to savannah environment at or near Namurungule during the upper Miocene. We find very little evidence to suggest that there was forest in the vicinity at the time of deposition.

FOSSIL ANTHROPOIDS FROM NACHOLA AND SAMBURU HILLS, SAMBURU DISTRICT, KENYA

During the 1982 expedition to Samburu Hills and Nachola, a number of hominoid fossils was found from two Miocene deposits. A small hominoid and a large late Miocene hominoid are contained in the fossils. The former most closely resembles Kenyapithecus africanus, and the latter may be ancestral to the extant African apes and hominoids, to gorilla alone, or not to any living hominoids. The various alternatives are discussed.

Earliest colobine skeletons from Nakali, Kenya

Old World monkeys represent one of the most successful adaptive radiations of modern primates, but a sparse fossil record has limited our knowledge about the early evolution of this clade. We report the discovery of two partial skeletons of an early colobine monkey (Microcolobus) from the Nakali Formation (9.8-9.9 Ma) in Kenya that share postcranial synapomorphies with extant colobines in relation to arboreality such as mediolaterally wide distal humeral joint, globular humeral capitulum, distinctly angled zona conoidea, reduced medial trochlear keel, long medial epicondyle with weak retroflexion, narrow and tall olecranon, posteriorly dislocated fovea on the radial head, low projection of the femoral greater trochanter, wide talar head with a greater rotation, and proximodistally short cuboid and ectocuneiform. Microcolobus in Nakali clearly differs from the stem cercopithecoid Victoriapithecus regarding these features, as Victoriapithecus is postcranially similar to extant small-sized terrestrial cercopithecines. However, degeneration of the thumb, a hallmark of modern colobines, is not observed, suggesting that this was a late event in colobine evolution. This discovery contradicts the prevailing hypothesis that the forest invasion by cercopithecids first occurred in the Plio-Pleistocene, and shows that this event occurred by the late Miocene at a time when ape diversity declined.

New geological and palaeontological age constraint for the gorilla–human lineage split

The palaeobiological record of 12 million to 7 million years ago (Ma) is crucial to the elucidation of African ape and human origins, but few fossil assemblages of this period have been reported from sub-Saharan Africa. Since the 1970s, the Chorora Formation, Ethiopia, has been widely considered to contain ~10.5 million year (Myr) old mammalian fossils. More recently, Chororapithecus abyssinicus, a probable primitive member of the gorilla clade, was discovered from the formation. Here we report new field observations and geochemical, magnetostratigraphic and radioisotopic results that securely place the Chorora Formation sediments to between ~9 and ~7 Ma. The C. abyssinicus fossils are ~8.0 Myr old, forming a revised age constraint of the human–gorilla split. Other Chorora fossils range in age from ~8.5 to 7 Ma and comprise the first sub-Saharan mammalian assemblage that spans this period. These fossils suggest indigenous African evolution of multiple mammalian lineages/groups between 10 and 7 Ma, including a possible ancestral-descendent relationship between the ~9.8 Myr old Nakalipithecus nakayamai and C. abyssinicus. The new chronology and fossils suggest that faunal provinciality between eastern Africa and Eurasia had intensified by ~9 Ma, with decreased faunal interchange thereafter. The Chorora evidence supports the hypothesis of in situ African evolution of the Gorilla–Pan–human clade, and is concordant with the deeper divergence estimates of humans and great apes based on lower mutation rates of ~0.5 × 10−9 per site per year (refs 13, 14, 15).

Fossiliferous Localities of the Nachola-Samburu Hills Area, Northern Kenya

In the four geographic/stratigraphic areas of the Samburu Hills and Nachola. west of Baragoi, Kenya. a significant number of fossiliferous localities was found. Nachola area is dated to the middle Miocene, the Namurungule Formation in Samburu Hills to the upper Miocene, Kongia area (0 the Mio-Pliocene and Holocene to the area near Suguta Valley and in the drainage systems of the Samburu Hills to the Holocene. The site BG X in Nachola yielded a number of fossils provisionally assigned to Kenyapitlzecus. An important large hominoid specimen occurred in Site SH n of the Namurungule Fonnation. Undoubtedly a great many additional sites await discovery.

A New Species of Bothriodontinae, Merycopotamus Thachangensis (Cetartiodactyla, Anthracotheriidae) from the Late Miocene of Nakhon Ratchasima, Northeastern Thailand

Abstract Merycopotamus thachangensis, sp. nov. (Cetartiodactyla, Anthracotheriidae, Bothriodontinae) was discovered from a mined sand pit in Tha Chang village in Nakhon Ratchasima Province, northeastern Thailand. The specimen is a nearly complete cranium with left P3-M3 and right M1-M3. It is the first known Merycopotamus in Thailand. The new species has a nearly divided mesostyle with a remnant at the base. No small crest is developed from the buccal style on upper molars. The postparacrista and premetacrista are parallel, pointing buccally to distobuccally. The major palatine foramen is positioned at P2–P3. The naso-frontal suture is lobe-like. There is a single supraorbital foramen with a distinct groove. There is no contact between the nasal and lacrimal bones. M. thachangensis shows a mixture of derived and primitive features that distinguish it from the previously known species of Merycopotamus. The new Thai species might have evolved from M. medioximus in the early late Miocene of Siwaliks, though the retention of and/or secondary reversal to primitive character states in M. thachangensis makes it difficult to determine the phylogenetic relationships of the new species to the other Merycopotamus species. Although the provenance of other mammalian fossils from the Tha Chang area is problematic, our analyses have indicated that they can be sorted into three fossil assemblages of middle Miocene, late Miocene and early Pleistocene age. M. thachangensis is most likely late Miocene in age, possibly late late Miocene.

New Specimens of Chilotheridium (Perissodactyla, Rhinocerotidae) from the Upper Miocene Namurungule and Nakali Formations, Northern Kenya

Abstract. Rhinocerotid fossils from the lower upper Miocene Namurungule and Nakali Formations, northern Kenya, are described. These materials reveal the following diagnostic characters of Chilotheridium pattersoni: a strongly constricted protocone with a flattened lingual wall, a hypocone groove, a developed crochet, and an antecrochet curved toward the entrance of the medisinus. Specimens previously described from the Namurungule Formation as rhinocerotids are re-identified as C. pattersoni. The Nakali Formation specimens presented in this study are the first discovery of C. pattersoni from this locality. In addition, deciduous teeth of C. pattersoni, which were unknown previously, are reported for the first time. This discovery of C. pattersoni extends its temporal range to the early late Miocene.