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Two upper molars of the Chalicotheriidae (Mammalia, Perissodactyla) from the upper Miocene (ca. 10 Ma) Nakali Formation of Nakali, central Kenya, are described. One is identified as M2. The other i...

Body and canine size dimorphism in fossils inform sociobehavioral hypotheses on human evolution and have been of interest since Darwin's famous reflections on the subject. Here, we assemble a large dataset of fossil canines of the human clade, including all available Ardipithecus ramidus fossils recovered from the Middle Awash and Gona research areas in Ethiopia, and systematically examine canine dimorphism through evolutionary time. In particular, we apply a Bayesian probabilistic method that reduces bias when estimating weak and moderate levels of dimorphism. Our results show that Ar. ramidus canine dimorphism was significantly weaker than in the bonobo, the least dimorphic and behaviorally least aggressive among extant great apes. Average male-to-female size ratios of the canine in Ar. ramidus are estimated as 1.06 and 1.13 in the upper and lower canines, respectively, within modern human population ranges of variation. The slightly greater magnitude of canine size dimorphism in the lower than in the upper canines of Ar. ramidus appears to be shared with early Australopithecus, suggesting that male canine reduction was initially more advanced in the behaviorally important upper canine. The available fossil evidence suggests a drastic size reduction of the male canine prior to Ar. ramidus and the earliest known members of the human clade, with little change in canine dimorphism levels thereafter. This evolutionary pattern indicates a profound behavioral shift associated with comparatively weak levels of male aggression early in human evolution, a pattern that was subsequently shared by Australopithecus and Homo.

Body and canine size dimorphism in fossils inform sociobehavioral hypotheses on human evolution and have been of interest since Darwin’s famous reflections on the subject. Here, we assemble a large dataset of fossil canines of the human clade, including all available Ardipithecus ramidus fossils recovered from the Middle Awash and Gona research areas in Ethiopia, and systematically examine canine dimorphism through evolutionary time. In particular, we apply a Bayesian probabilistic method that reduces bias when estimating weak and moderate levels of dimorphism. Our results show that Ar. ramidus canine dimorphism was significantly weaker than in the bonobo, the least dimorphic and behaviorally least aggressive among extant great apes. Average male-to-female size ratios of the canine in Ar. ramidus are estimated as 1.06 and 1.13 in the upper and lower canines, respectively, within modern human population ranges of variation. The slightly greater magnitude of canine size dimorphism in the lower than in the upper canines of Ar. ramidus appears to be shared with early Australopithecus, suggesting that male canine reduction was initially more advanced in the behaviorally important upper canine. The available fossil evidence suggests a drastic size reduction of the male canine prior to Ar. ramidus and the earliest known members of the human clade, with little change in canine dimorphism levels thereafter. This evolutionary pattern indicates a profound behavioral shift associated with comparatively weak levels of male aggression early in human evolution, a pattern that was subsequently shared by Australopithecus and Homo.

The middle Miocene stem kenyapithecine Nacholapithecus kerioi (16–15 Ma; Nachola, Kenya) is represented by a large number of isolated fossil remains and one of the most complete skeletons in the hominoid fossil record (KNM-BG 35250). Multiple fieldwork seasons performed by Japanese–Kenyan teams during the last part of the 20th century resulted in the discovery of a large sample of Nacholapithecus fossils. Here, we describe the new femoral remains of Nacholapithecus. In well-preserved specimens, we evaluate sex differences and within-species variation using both qualitative and quantitative traits. We use these data to determine whether these specimens are morphologically similar to the species holotype KNM-BG 35250 (which shows some plastic deformation) and to compare Nacholapithecus with other Miocene hominoids and extant anthropoids to evaluate the distinctiveness of its femur. The new fossil evidence reaffirms previously reported descriptions of some distal femoral traits, namely the morphology of the patellar groove. However, results also show that relative femoral head size in Nacholapithecus is smaller, relative neck length is longer, and neck–shaft angle is lower than previously reported for KNM-BG 35250. These traits have a strong functional signal related to the hip joint kinematics, suggesting that the morphology of the proximal femur in Nacholapithecus might be functionally related to quadrupedal-like behaviors instead of more derived antipronograde locomotor modes. Results further demonstrate that other African Miocene apes (with the exception of Turkanapithecus kalakolensis) generally fall within the Nacholapithecus range of variation, whose overall femoral shape resembles that of Ekembo spp. and Equatorius africanus. Our results accord with the previously inferred locomotor repertoire of Nacholapithecus, indicating a combination of generalized arboreal quadrupedalism combined with other antipronograde behaviors (e.g., vertical climbing).

Sexual size dimorphism in the African fossil ape Proconsul nyanzae (18 million years ago, 18 Ma) has been previously documented. However, additional evidence for sexual dimorphism in Miocene hominoids can provide great insight into the history of extant hominoid mating systems. The present study focused on body mass (BM) sexual dimorphism in Nacholapithecus kerioi from the Middle Miocene (16–15 Ma) in Africa. Bootstrap analysis revealed that P. nyanzae BM sexual dimorphism was lower than that in Pan troglodytes, which exhibits moderate sexual dimorphism, as reported previously. The same simulation revealed that BM sexual dimorphism of N. kerioi was comparable with that in Gorilla spp.; i.e., the males were approximately twice as large as the females. High sexual dimorphism in extant apes is usually indicative of a polygynous social structure (gorilla) or solitary/fission-fusion social system (orangutan). However, because of the high proportion of adult males in this fossil assemblage, the magnitude of dimorphism inferred here cannot be associated with a gorilla-like polygynous or oranguran-like solitary/fission-fusion social structure, and may reflect either taphonomic bias, or some other social structure. Extant hominoids have a long evolutionary history owing to their deep branching, comprising only a few existing members of the original highly successful group. Therefore, it is not surprising that the mating systems of extant hominoids fail to provide fossil apes with a perfect “model”. The mating systems of extinct hominoids may have been more diverse than those of extant apes.

Several isolated cheek teeth and mandibular specimens of Rhinocerotidae (Mammalia, Perissodactyla) from the upper Miocene Namurungule Formation in Samburu Hills, Kenya, are redescribed. Previously, these specimens had been identified as Chilotheridium pattersoni, Chilotheridium sp., Paradiceros mukirii, and Paradiceros sp. They are reidentified here as documenting the genus Brachypotherium based on their bucco-lingually broad molariform upper premolars with short crochet and flattened buccal walls on both upper and lower molars, the latter having a shallow external groove. Comparisons with other Brachypotherium species suggest that the present specimens belong to Brachypotherium sp. cf. B. minor. The presence of Brachypotherium in the Samburu Hills, at ca. 9.5 Ma, is concordant with the paleoenvironment (presence of lacustrine and river environments) known for this locality during the early late Miocene.

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–m...

An upper incisor and upper and lower cheek teeth of Rhinocerotidae from the Upper Miocene of Nakali in central Kenya are described. Those specimens are identified as Diceros sp. The present study confirms the presence of Diceros in sub-Saharan East Africa during Vallesian as noted by several studies. The present result and the fossil records of Diceros in Africa and Eurasia suggest that Diceros might have migrated to Eurasia from Africa by Vallesian, although more fossil records and detailed phylogenetic analysis of Diceros are needed to discuss this hypothesis.

Several rhinocerotid cheek teeth and mandibular fragments from the upper Miocene of the Samburu Hills and Nakali in northern Kenya are described. These specimens show characteristics that place them in the Tribe Elasmotheriini such as a constricted protocone, a developed antecrochet, and coronal cement. The present specimens are compared with other Elasmotheriini species from Eurasia and sub-Saharan East Africa. They are found to be morphologically different from the previously known species of Elasmotheriini. Morphologically, they are most similar to Victoriaceros kenyensis from the middle Miocene of Kenya, but differ from V. kenyensis in having the upper molars with the simple crochet, lingual groove of the protocone and enamel ring in the medisinus. Therefore, the present specimens are assigned to a new genus and species of Elasmotheriini: Samburuceros ishidai. A cladistic analysis tentatively places S. ishidai nov. gen., nov. sp. as a sister taxon of V. kenyensis. However, questions remain regarding a further detailed discussion of the phylogenetic relationship between the African Elasmotheriini and other Eurasian taxa because of the incompleteness of the specimens from Africa, as already noticed by several researchers.

Objectives The bony labyrinth of the inner ear has special relevance when tracking phenotypic evolution because it is often well preserved in fossil and modern primates. Here we track the evolution of the bony labyrinth of anthropoid primates during the Mio−Plio−Pleistocene—the time period that gave rise to the extant great apes and humans. Materials and Methods We use geometric morphometrics to analyze labyrinthine morphology in a wide range of extant and fossil anthropoids, including New World and Old World monkeys, apes, and humans; fossil taxa are represented by Aegyptopithecus, Microcolobus, Epipliopithecus, Nacholapithecus, Oreopithecus, Ardipithecus, Australopithecus, and Homo. Results Our results show that the morphology of the anthropoid bony labyrinth conveys a statistically significant phylogenetic signal especially at the family level. The bony labyrinthine morphology of anthropoids is also in part associated with size, but does not cluster by locomotor adaptations. The Miocene apes examined here, regardless of inferred locomotor behaviors, show labyrinthine morphologies distinct from modern great apes. Discussion Our results suggest that labyrinthine variation contains mixed signals and alternative explanations need to be explored, such as random genetic drift and neutral phenotypic evolution, as well as developmental constraints. The observed pattern in fossil and extant hominoids also suggests that an additional factor, for example, prenatal brain development, could have potentially had a larger role in the evolutionary modification of the bony labyrinth than hitherto recognized.

After a long period of inactivity, recent excavations at the late Miocene Maragheh Formation unexpectedly resulted in the discovery of the first fossil hominoid and second Mesopithecus remains from this area. The discovery motivated a new international initiative to conduct research in these rich fossil sites. These studies focused on the fossil hominoid and its locality, aiming to reveal more about the context of this fossil discovery. Detailed stratigraphy, sedimentology and magnetostratigraphy studies were conducted. New samples from volcaniclastic key horizons (pumice beds) in Dareh Gorg, where the hominoid fossil site is located, were dated by radiometric methods. The radiometric age determinations provide a firm tie-point for the geochronology. The polarity pattern in the palaeomagnetically investigated section corroborates the K-Ar results. The preliminary magnetostratigraphic results suggest that the hominoid locality can be correlated to the normal polarity chron C4n.2n (8.108–7.695 Ma), C4n.1n (7.642–7.528 Ma) or C3Br.1n (7.285–7.251 Ma), placing it at intervals corresponding to the mammal units MN11 or possibly early MN12. The study of fossil hominoid indicates broad affinities with a number of contemporaneous taxa from the Balkan-Iranian palaeoprovince, as well as Siwaliks and southeast Asia. A preliminary analysis of the accompanying (in situ) fauna at the hominoid site indicates the highest similarity of this level to Turolian hominoid- and Mesopithecus-bearing localities in Turkey, Greece and Bulgaria. However, some environmental differences are observed among these localities, based on their faunal structure and taxon properties, as well as in the different masticatory adaptations of their hominoids.

Miocene hominoid fossils are known from Africa and Eurasia, in the latter ranging widely from western Europe to Anatolia and from South Asia to Southeast/East Asia. Iran is located between the known western and eastern Eurasian hominoid distributions and is potentially important in understanding Miocene hominoid dispersal patterns. Maragheh is a late Miocene fossil locality in northwestern Iran, well known since the nineteenth century for its abundant mammalian fossils. However, until now, the only primate fossils reported from Maragheh or Iran were the Old World monkey Mesopithecus pentelicus. Recent field research at Maragheh has changed this situation by the discovery of the first hominoid fossil from Iran, a maxillary fragment with well-preserved second and third molars. Here, we provide a detailed description of this new specimen, comparing it with other similarly large-sized Eurasian late Miocene hominoids, Ouranopithecus, Ankarapithecus, Sivapithecus, and Indopithecus. Molar morphology of the Maragheh hominoid is similar to that of these Eurasian Miocene genera, with only minor differences in morphology and wear pattern. Based on the presently available materials, we tentatively prefer the interpretation that the Maragheh hominoid may be related more closely to either Ankarapithecus or Sivapithecus rather than to Ouranopithecus, but the fragmentary nature of the fossil makes evaluations difficult. Future discoveries of this Iranian hominoid are needed to determine its phylogenetic position with more certainty.

Most Plio-Pleistocene sites in the Gregory Rift Valley that have yielded abundant fossil hominins lie on the Rift Valley floor. Here we report a new Pliocene site, Kantis, on the shoulder of the Gregory Rift Valley, which extends the geographical range of Australopithecus afarensis to the highlands of Kenya. This species, known from sites in Ethiopia, Tanzania, and possibly Kenya, is believed to be adapted to a wide spectrum of habitats, from open grassland to woodland. The Kantis fauna is generally similar to that reported from other contemporaneous A. afarensis sites on the Rift Valley floor. However, its faunal composition and stable carbon isotopic data from dental enamel suggest a stronger C4 environment than that present at those sites. Although the Gregory Rift Valley has been the focus of paleontologists' attention for many years, surveys of the Rift shoulder may provide new perspective on African Pliocene mammal and hominin evolution, ケニア・ナイロビ郊外で初めて発見されたアウストラロピテクス. 京都大学プレスりリス. 2016-03-24.

Objectives The carpal bones of the middle Miocene hominoid Nacholapithecus kerioi are described based on new materials. Materials and Methods The materials comprise a trapezoid, three capitates, two hamates, a centrale, a lunate, a triquetrum, and a pisiform, collected during the 2001 and 2002 field seasons from Nachola, Kenya. We also describe a pisiform recently assigned to the type specimen of N. kerioi, KNM-BG 35250. Results In the Nacholapithecus wrist, the ulnar styloid process articulates with both the triquetrum and pisiform, and the triquetrum facet on the hamate is relatively proximodistally oriented in dorsal view. The Nacholapithecus capitate possesses a moderate distopalmar hook-like process and separated radial articular facets for the trapezoid and the second metacarpal due to the carpometacarpal ligament attachment that is absent in the Proconsul capitate. Discussion The carpal anatomy of Nacholapithecus is similar to that of the early Miocene hominoid Proconsul. However, Nacholapithecus wrist anatomy appears to exhibit slightly more emphasized stability. Am J Phys Anthropol, 2016. © 2016 Wiley Periodicals, Inc.

A new species of Nyanzachoerus (Mammalia, Artiodactyla, Suidae, Tetraconodontinae), Nyanzachoerus nakaliensis, is described on the basis of gnathodental specimens from the basal upper Miocene Nakali Formation (ca. 10 Ma) of central Kenya. Ny. nakaliensis is characterized by a lower crown height and relatively weaker furrows of the molars and proportionally larger P3–P4 compared to M3 among the species of the genus. It is the oldest and morphologically most primitive species of the genus. It shows close morphological similarities of the dentition with the Pliocene Asian tetraconodontine genus Sivachoerus, implying a possible closer phyletic relationship of Sivachoerus prior with Ny. nakaliensis rather than with Nyanzachoerus tulotos or Nyanzachoerus devauxi. This phyletic relationship implies a possibility that S. prior diverged from a stock of Ny. nakaliensis during the early late Miocene (Tortonian) in East Africa and then the lineage moved from East Africa to Asia. Finally, it should be stressed that there seems to be a problem of the paraphyly of the genus Nyanzachoerus.

A new caudal thoracic and a new lumbar vertebra of Nacholapithecus kerioi, a middle Miocene hominoid from northern Kenya, are reported. The caudal thoracic vertebral body of N. kerioi has a rounded median ventral keel and its lateral sides are moderately concave. The lumbar vertebral body has an obvious median ventral keel. Based on a comparison of vertebral body cranial articular surface size between the caudal thoracic vertebrae in the present study and one discussed in a previous study (KNM-BG 35250BO, a diaphragmatic vertebra), N. kerioi has at least two post-diaphragmatic vertebrae (rib-bearing lumbar-type thoracic vertebrae), unlike extant hominoids. It also has thick, rounded, and moderately long metapophyses on the lumbar vertebra that project dorsolaterally. The spinous process bases of its caudal thoracic and lumbar vertebrae originate caudally between the postzygapophyses, as described previously in the KNM-BG 35250 holotype specimen. In other words, the postzygapophyses of N. kerioi do not project below the caudal border of the spinous processes, similar to those of extant great apes, and unlike small apes and monkeys, which have more caudally projecting postzygapophyses. Nacholapithecus kerioi has a craniocaudally expanded spinous process in relation to vertebral body length, also similar to extant great apes. Both these spinous process features of N. kerioi differ from those of Proconsul nyanzae. The caudal thoracic vertebra of N. kerioi has a caudally-directed spinous process, whose tip is tear-drop shaped. These features resemble those of extant apes. The morphology of the spinous process tips presumably helps vertebral stability by closely stacking adjacent spinous process tips as seen in extant hominoids. The morphology of the spinous process and postzygapophyses limits the intervertebral space and contributes to the stability of the functional lumbar region as seen in extant great apes, suggesting that antipronograde activity was included in the positional behavior of N. kerioi.

A trigonid of a lower molar of a primitive, large hippopotamus from the upper lower Miocene of Mfwangano Island in southwestern Kenya is described. The molar trigonid is similar in size to that of living hippopotamuses, and is comparable in morphology to that of kenyapotamine hippopotamids (Mammalia, Cetartiodactyla) in having a brachyodont crown, bunodont cusps, an M-like structure on the distal trigonid wall, a single-ridged premetacristid, and a buccolingually bifurcate mesial root, and in lacking a paraconid. On the basis of its size and morphology, the specimen appears to be assignable to Kulutherium, which is a putative kenyapotamine previously known from the upper lower Miocene of Kenya and is so far represented only by the upper dentition. The present specimen provides additional evidence that a hippopotamus-sized, large hippopotamid was already living during the early Miocene. If it proves to be Kulutherium, it provides additional evidence that Kulutherium should be assigned to the Keny...

Two large rodents from the Middle Miocene (13.0–12.4 Ma) were discovered at the Chiang Muan Coal Mine, northern Thailand. One, a beaver (Anchitheriomys, Castoridae), has large cheek teeth with a hi...

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.

Clarifying morphological variation among African and Eurasian hominoids during the Miocene is of particular importance for inferring the evolutionary history of humans and great apes. Among Miocene hominoids, Nakalipithecus and Ouranopithecus play an important role because of their similar dates on different continents. Here, we quantify the lower fourth deciduous premolar (dp4) inner morphology of extant and extinct hominoids using a method of morphometric mapping and examine the phylogenetic relationships between these two fossil taxa. Our data indicate that early Late Miocene apes represent a primitive state in general, whereas modern great apes and humans represent derived states. While Nakalipithecus and Ouranopithecus show similarity in dp4 morphology to a certain degree, the dp4 of Nakalipithecus retains primitive features and that of Ouranopithecus exhibits derived features. Phenotypic continuity among African ape fossils from Miocene to Plio-Pleistocene would support the African origin of African apes and humans (AAH). The results also suggest that Nakalipithecus could have belonged to a lineage from which the lineage of Ouranopithecus and the common ancestor of AAH subsequently derived. (C) 2016 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

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.

In primates, tail length is subject to wide variation, and the tail may even be absent. Tail length varies greatly between each species group of the genus Macaca, which is explained by climatic factors and/or phylogeographic history. Here, tail length variability was studied in hybrids of the Japanese (M. fuscata) and Taiwanese (Macaca cyclopis) macaque, with various degrees of hybridization being evaluated through autosomal allele typing. Relative tail length (percent of crown-rump length) correlated well with the number of caudal vertebrae. Length profiles of caudal vertebrae of hybrids and parent species revealed a common pattern: the length of several proximal-most vertebrae do not differ greatly; then from the third or fourth vertebra, the length rapidly increases and peaks at around the fifth to seventh vertebra; then the length plateaus for several vertebrae and finally shows a gentle decrease. As the number of caudal vertebrae and relative tail length increase, peak vertebral length and lengths of proximal vertebrae also increase, except that of the first vertebra, which only shows a slight increase. Peak vertebral length and the number of caudal vertebrae explained 92 % of the variance in the relative tail length of hybrids. Relative tail length correlated considerably well with the degree of hybridization, with no significant deviation from the regression line being observed. Thus, neither significant heterosis nor hybrid depression occurred.

Stable isotope and molecular data suggest that C 4 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 C 3 to mixed C 3 /C 4 or C 4 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 C 4 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 C 4 grasslands in this part of the Late Miocene. Bovids and hippopotamids followed suit with individuals that had C 4 -dominated (>65%) diets by 7.4 Ma. Suids adopted C 4 -dominated diets between 6.5 and 4.2 Ma. Gomphotheriids and elephantids had mostly C 3 -dominated diets through 9.3 Ma, but became dedicated C 4 grazers by 6.5 Ma. Deinotheriids and giraffids maintained a predominantly C 3 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.

We report in this paper two unusual cases of M1 agenesis recently discovered in Japanese macaques (Macaca fuscata). Molar agenesis is the congenital absence of molars. In general, molar agenesis occurs from the posterior molars. In most cases, missing teeth are third molars. Second molars may occasionally be absent in addition to the third molars. However, the congenital absence of first molars is hardly observed in humans, and to our knowledge, no case has been reported in other primates. In addition to the rareness of first molar agenesis, the present cases in M. fuscata are also quite unusual, because the posterior molars (M2 and M3) were completely preserved in contrast to the ordinary pattern of molar reduction. Interestingly, the two cases of the present study were observed in a single maternal lineage (a mother and her son), suggesting that M1 agenesis in these Japanese macaques is genetically inherited.

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. Am J Phys Anthropol 143:365-382, 2010. © 2010 Wiley-Liss, Inc.

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 ...

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.

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.

We describe the postcranial bones of a partial skeleton of a male infant Nacholapithecus kerioi (KNM-BG 37800) from the Middle Miocene of Kenya. The skeletal elements are associated with dental remains and its age is presumed to be 6–15 months based on a comparison with an infant Proconsul heseloni with a similar dental growth stage. The postcranial elements include the left scapula, a lumbar vertebra, left distal humerus, right proximal ulna, right radius, right and left proximal femora, a proximal fragment of metatarsal, and proximal and intermediate phalanges. Its body mass was estimated as 3.0 kg from shaft dimensions of the humerus and femur. At this early postnatal developmental stage, N. kerioi can be distinguished from P. heseloni in several postcranial features: a caudally projecting lumbar spinous process, strong dorsal divergence of the scapular spine, a coronoid fossa which is more developed than the radial fossa, higher neck shaft angle of the femur, taller trochlea of phalanges, and a lower brachial index. These features, except for the last, agree with the previously proposed positional behavioral reconstruction of N. kerioi, in which vertical climbing, orthograde clambering, transferring, or bridging are relatively important compared with P. heseloni. The apparently low brachial index results from a comparatively short radius for the predicted body mass. This might imply a relatively slow pace of growth in the radius of N. kerioi. However, it might result from body mass overestimation, incorrect length reconstruction, or individual variation. Its interpretation must await further specimens.

This study describes two new sacral specimens of Nacholapithecus kerioi, KNM-BG 42753I and KNM-BG 47687A, from the Aka Aiteputh Formation in Nachola, northern Kenya, excavated in 2002. They are of roughly equal size and are considered to belong to males. When scaled by body mass, the lumbosacral articular surface area of the better preserved specimen, KNM-BG 42753I, is smaller than that in Old World monkeys but similar to that in extant great apes and New World monkeys, as well as Proconsul nyanzae. The relatively narrow dimensions of the first sacral vertebral body in the transverse and sagittal planes are characteristics of N. kerioi and P. nyanzae and similar to those of extant great apes. In N. kerioi, lumbosacral surface area relative to body mass is small. This may simply be an extension of a trend from the previously reported small thoracolumbar vertebrae to the sacrum. ​The first sacral vertebrae of N. kerioi and Epipliopithecus vindobonensis have a higher craniocaudal vertebral body reduction (CVR; a higher CVR indicates a wider cranial width relative to a narrower caudal width), similar to that in Old World monkeys. Old World monkeys have a higher CVR, and usually have three sacral vertebrae, fewer than seen in extant great apes, which have a lower CVR and four to six (sometimes as many as eight) sacral vertebrae. New World monkeys have a lower CVR than Old World monkeys, but generally possess only three sacral vertebrae, and have a large caudal articular surface, which may be related, at least in the Atelidae, to the grasping ability of their tails. The possibility that N. kerioi had only three sacral vertebrae cannot be ruled out, because E. vindobonensis and Old World monkeys, with higher CVRs, have sacra consisting of three sacral vertebrae.

The carpal bones of the middle Miocene hominoid Nacholapithecus kerioi are described based on new materials.The materials comprise a trapezoid, three capitates, two hamates, a centrale, a lunate, a triquetrum, and a pisiform, collected during the 2001 and 2002 field seasons from Nachola, Kenya. We also describe a pisiform recently assigned to the type specimen of N. kerioi, KNM-BG 35250.In the Nacholapithecus wrist, the ulnar styloid process articulates with both the triquetrum and pisiform, and the triquetrum facet on the hamate is relatively proximodistally oriented in dorsal view. The Nacholapithecus capitate possesses a moderate distopalmar hook-like process and separated radial articular facets for the trapezoid and the second metacarpal due to the carpometacarpal ligament attachment that is absent in the Proconsul capitate.The carpal anatomy of Nacholapithecus is similar to that of the early Miocene hominoid Proconsul. However, Nacholapithecus wrist anatomy appears to exhibit slightly more emphasized stability. Am J Phys Anthropol 160:469-482, 2016. © 2016 Wiley Periodicals, Inc.

A paleomagnetic study has been conducted on the Miocene Chiang Muan Formation in northern Thailand, in order to provide a chronology for the earliest large-bodied Miocene hominoid in Southeast Asia. The Chiang Muan Formation is mainly composed of clay, silt and sand beds, indicating lacustrine and fluvial environments. Paleomagnetic samples were collected from 124 horizons along an approximately 150 m thick section from the Chiang Muan Formation at the opencast Chiang Muan Mine. Rock magnetic experiments and stepwise thermal demagnetizations revealed that the main carrier of the magnetization of the sediments is magnetite and the samples have stable magnetization. Exceptionally, stable magnetization is also carried by hematite, which is represented by red colored sediments. Characteristic remanent magnetization (ChRM) directions, calculated by the principal component analysis, revealed normal or reversed polarities of magnetization, which allow the application of the reversal test of McFadden and McElhinny [McFadden, P.L., McElhinny, M.W., 1990. Classification of the reverse test in paleomagnetism. Geophys. Int. 103, 725–729]. The mean paleomagnetic directions of the normal and reversed polarities passed the reversal test with a classification C, indicating that the Chiang Muan Formation preserved the primary magnetization. In total, five normal and four-reversed polarity zones are recognized from the studied section. Based on paleontological age constraints, this magnetostratigraphic column of the Chiang Muan Formation correlates best with Chron C5AAn-C5n of the geomagnetic polarity time scale (GPTS) from the geological time scale (GTS2004) developed by Gradstein et al. [Gradstein, F., Ogg, J., Smith, A. (Eds.) 2004. A Geological Time Scale 2004. Cambridge Univ. Press, Cambridge, UK, p. 589]. This correlation revealed that sedimentation of the Chiang Muan Formation began approximately at 13 Ma and continued until 9.8 Ma with a mean sedimentation rate of approximately 4.2 cm/ky. The age of the earliest Southeast Asian hominoid is between 12.4 and 13.0 Ma.

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 germ's development that causes intranasal teeth as supernumerary teeth, and another is the problem of tooth germ's 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 br...

Atlas bridging represents the formation of a bony bridge over the vertebral artery groove of the first cervical vertebra. There are two kinds of bridging, the ‘posterior bridge’ and the ‘lateral bridge’. Such bridges may occur together or separately, and bilaterally or unilaterally. We investigated ontogenetic change and geographical variation of atlas bridging in Japanese macaques (Macaca fuscata) to clarify age effects and frequencies within a species. A total of 193 skeletal specimens of Japanese macaques of known chronological age were examined for ontogenetic change. Atlas bridges, both posterior and lateral, were present in most adults; they were found to develop at an early age. The posterior and lateral bridges were found complete at around 400–830 and 700–2500 days, respectively, after birth. A total of 328 Japanese macaques (Macaca fuscata fuscata and Macaca fuscata yakui) from seven regions were used in the study of geographical variation. Both posterior and lateral bridges were commonly observed regardless of region, with a tendency for a slightly lower prevalence of the lateral bridge than the posterior bridge. Atlas bridging did not differ in frequency between the right and left sides. Sexual differences were not significant in most of the populations. As for the lateral bridge, the Shimane population had a lower frequency than that found in the other populations. However, even considering such intraspecific variation, atlas bridging can be considered as a stable trait within Japanese macaques, the prevalence of which is remarkably higher than in hominoids.

The discovery of a rich and diverse vertebrate fauna in the Middle Miocene Muruyur Formation (ca. 14.5 Ma), Tugen Hills, Kenya, provides a rare view of the structure of the catarrhine fauna from this time period. Up to 2002, more than 140 catarrhine specimens have been collected from three sites (Kipsaraman, Keturo, and Cheparawa) represented by 199 teeth. At least six taxa are present, five ‘apes’ (hominoids sensu lato) and one cercopithecoid. Three of the taxa are new species. The Kipsaraman catarrhine fauna has some similarities to those of Maboko (ca. 15 Ma) and Fort Ternan (ca. 13.7 Ma), western Kenya, but it differs markedly from the Nachola (ca. 16 Ma) one, not only in the relative abundance of hominoids versus cercopithecoids, but also in the taxa represented. At Maboko and Kipsaraman, the most abundant catarrhine fossils are cercopithecoids, whereas these are rare at Nachola and unknown at Fort Ternan. At Kipsaraman, Maboko, and Fort Ternan, small ‘ape’ fossils are common, whereas they are absent from Nachola. Nyanzapithecus or a similar genus is present, but rare at all four sites. Kenyapithecus is present at Maboko, Fort Ternan, and Kipsaraman, but is absent from Nachola, its place being taken by Nacholapithecus which is abundant at the site. The catarrhine faunas from these Middle Miocene localities indicate that environmental conditions within East Africa were highly variable between 16 and 13.7 Ma.

The Thai-Japanese Paleontological Expedition Team (TJPET) has been conducting paleontological and geological fieldwork in Thailand for a number of years. In January 2000, an upper molar (CMu6-1’00) of a large-bodied Miocene hominoid was found by TJPET in a lignite mine in the Chiang Muan basin, northern Thailand. It was the first record of a Miocene hominoid from a Southeast Asian country. Two years later, TJPET found a second hominoid specimen (CMu15-5’01) in the same lignite mine. The second specimen was collected from the Upper Lignite Member, while the first one had come from the Lower Lignite Member. The age of Chiang Muan is estimated to be at around the boundary of the Middle/Late Miocene (ca. 10–12 Ma) based on mammalian fauna and paleomagnetic study. There may be several hundred thousand years temporal difference between the Upper and Lower Lignite Members. Chaimanee et al. (2003) reported more hominoid specimens from the same site, and created a new species, cf. Lufengpithecus chiangmuanensis. The taxonomic status of the Chiang Muan hominoids, however, is still a matter of debate. Nevertheless, the discovery of Miocene hominoids from Chiang Muan has revealed the potential of Thailand for understanding hominoid evolution in Southeast Asia.