Yutaka Kunimatsu

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.

Preliminary analysis of Nacholapithecus scapula and clavicle from Nachola, Kenya

The Miocene ape Nacholapithecus is known from rather complete skeletons; some of them preserve the shoulder joint, identified by three scapulae and one clavicle. Comparisons made with other Miocene and living apes (Proconsul, Equatorius, Ugandapithecus) suggest that the mobility of the scapulohumeral joint was important, and scapular features such as the morphology and position of the spine and the morphology of the acromion and axillary border resemble those of climbing arboreal primates except for chimpanzees, gorillas, or orang-utans. From the size of the scapula (male Nasalis size), it is clear that the animal is smaller than an adult chimpanzee, but the clavicle is almost as relatively long as those of chimpanzees. Some features closer to colobine morphology reinforce the hypothesis that Nacholapithecus was probably a good climber and was definitely adapted for an arboreal life.

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.

Intra- and interspecific variation in macaque molar enamel thickness

Enamel thickness has played an important role in studies of primate taxonomy, phylogeny, and functional morphology, although its variation among hominins is poorly understood. Macaques parallel hominins in their widespread geographic distribution, relative range of body sizes, and radiation during the last five million years. To explore enamel thickness variation, we quantified average and relative enamel thickness (AET and RET) in Macaca arctoides, Macaca fascicularis, Macaca fuscata, Macaca mulatta, Macaca nemestrina, and Macaca sylvanus. Enamel area, dentine area, and enamel-dentine junction length were measured from mesial sections of 386 molars scanned with micro-computed tomography, yielding AET and RET indices. Intraspecific sex differences were not found in AET or RET. Macaca fuscata had the highest AET and RET, M. fascicularis showed the lowest AET, and M. arctoides had the lowest RET. The latitudinal distribution of macaque species was associated with AET for these six species. Temperate macaques had thicker molar enamel than did tropical macaques, suggesting that thick enamel may be adaptive in seasonal environments. Additional research is needed to determine if thick enamel in temperate macaques is a response to intensified hard-object feeding, increased abrasion, and/or a broader diet with a greater range of food material properties. The extreme ecological flexibility of macaques may prohibit identification of consistent trends between specific diets and enamel thickness conditions. Such complications of interpretation of ecological variability, dietary diversity, and enamel thickness may similarly apply for fossil Homo species.

Un nouveau genre d'hominoide du Miocene inferieur d'Afrique orientale : Ugandapithecus major (Le Gros Clark & Leakey, 1950)

Abstract It has been known for a long time that the dentition of P. major differs in several features from those of P. africanus (the type species of the genus) and P. nyanzae (including P. heseloni ). Newly discovered postcranial bones from Napak assigned to Proconsul major differ markedly from those assigned to Proconsul species from the Kenyan sites of Koru, Songhor, Mfwangano and Rusinga and reveal that the species concerned differs from Proconsul at least at the generic level. We accordingly erect a new genus, Ugandapithecus , for the species Proconsul major Le Gros Clark & Leakey, 1950 [18] . A few of the dental and postcranial remains from Moroto, Uganda, are indistinguishable from those from Napak U. major , whereas others, including the Moroto palate (the holotype of Morotopithecus bishopi ) and much of a femur attributed to the latter species differ markedly from it. Thus at Moroto there are two genera of large bodied hominoids. It is not known to which of the genera the Moroto vertebral remains pertain, but they probably belong to U. major .

An exploratory study on the combined effects of external and internal morphology on load dissipation in primate capitates: its potential for an understanding of the positional and locomotor repertoire of early hominins.

This pilot study explored whether the redirection of stress through trabeculae within morphologically constrained capitates provides information about habitual/positional behaviours unavailable from the study of external morphology alone. To assess this possibility, an experimental finite element approach was taken, whereby no attempt was made to reconstruct the actual magnitudes and loading conditions experienced by the capitates in vivo. Rather, this work addressed fundamental biological questions relating to bone plasticity, i.e. internal versus external bone morphology. The capitates of 7 species with different and – in the case of fossils – inferred locomotor behaviours were selected. Virtual models of capitates were created, scaled to the same size and subjected to the same theoretical load. In the first set of analyses, models were assigned the material properties of bone throughout, whereas in the second set, models were assigned 11 different material properties representing the trabecular architecture derived from high-resolution CT. Species with arboreal behaviours consistently redirected loads towards the ulnar aspect of the capitate when trabeculae were introduced, while terrestrial species, and the bipedal Homo, redirected stress towards the radial side. From these preliminary analyses, it is tentatively concluded that Australopithecus anamensis habitually engaged in arboreal behaviours, whereas Australopithecus afarensis did not.

Systematic morphology and evolutionary anatomy of the autonomic cardiac nervous system in the lesser apes, gibbons (hylobatidae).

We examined the morphology of the autonomic cardiac nervous system (ACNS) on 20 sides of 10 gibbons (Hylobatidae) of three genera, and we have inferred the evolution of the anatomy of the primate ACNS. We report the following. (1) Several trivial intraspecific and interspecific variations are present in gibbons, but the general arrangement of the ACNS in gibbons is consistent. (2) Although the parasympathetic vagal cardiac nervous system is extremely consistent, the sympathetic cardiac nervous system, such as the composition of the sympathetic ganglia and the range of origin of the sympathetic cardiac nerves, exhibit topographical differences among primates. (3) The vertebral ganglion, seldom observed in the Old World monkeys (Cercopithecidae), was consistently present in gibbons as well as in humans. (4) There are fewer thoracic ganglia contributing to the cervicothoracic ganglion in humans than in gibbons and in gibbons than in Old World monkeys. (5) The superior cardiac nerve originating from the superior cervical ganglion, rarely observed in Old World monkeys but commonly observed in humans, was present in 13 of 20 sides (65%), mostly on the left. Accordingly, the ACNS morphology exhibits evolutionary changes within the primate lineage. These evolutionary differences between Old World monkeys, gibbons, and humans are most parsimoniously interpreted as resulting from regular changes in the lineages leading from their common ancestor to the extant species that we dissected. They include the reduction in the number of thoracic ganglia contributing to the cervicothoracic ganglion and the expansion of the range of the cardiac nervous origin. Anat Rec, 291:939–959, 2008.

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.

Intranasal tooth in Japanese macaque (Macaca fuscata)

ABSTRACT A rare case of the dental anomaly, viz., intranasal tooth was observed in a female Japanese macaque monkey (Macaca fuscata) (K-105) from Kinkazan Island, Miyagi Prefecture in northeastern Japan. Intranasal tooth is an ectopic tooth erupted into the nasal cavity. The intranasal tooth of K-105 is a left P4 based on the morphology, and is not a supernumerary tooth. Intranasal tooth is one symptom, but, its etiology may be divided into two; one is the problem of tooth germs development that causes intranasal teeth as supernumerary teeth, and another is the problem of tooth germs migration that causes intranasal teeth as missing teeth from the dentition. In our sample, the tooth germ of the left P4 probably moved from the normal position to the nasal floor in an early life stage and developed there. The crown proportion is different from the typical P4 in the Kinkazan specimens. K-105 has relatively short buccolingual breadths of P4 on both sides. The intranasal tooth may have been an obstacle to breathing to some extent, yet K-105 survived until adulthood. The disadvantage of having an intranasal tooth in this case was not serious.