Masato Nakatsukasa

Kyoto University | Kyodai · Department of Zoology

Objectives The elbow of Nacholapithecus has been extensively described qualitatively, however its ulnar morphology has never been the focus of an in‐depth quantitative analysis before. Hence, our main aim is quantifying the proximal ulnar morphology in Nacholapithecus and exploring whether it is similar to those of Equatorius and Griphopithecus as...

Objectives Metatarsal bones constitute a key functional unit of the foot in primates. While the form‐function relationships of metatarsals have been extensively studied, particularly in relation to the loss of the grasping ability of the foot in humans in contrast to apes, the effect of phyletic history on the metatarsal morphology and its variabil...

This study aims to discriminate cercopithecid taxa of higher taxonomic levels (subfamily, tribe, subtribe, and genus) on the basis of corpus shape in transverse cross-section at the M 1 -M 2 junction and to assess its variation using 2D geometric morphometrics. Specifically, we evaluated the effect of allometry and sexual dimorphism on differences...

The symphyseal anatomy of extant and fossil cercopithecids has not yet been demonstrated as a useful tool for taxonomic discrimination, and the source of variation in cercopithecid symphysis has not been addressed on a broad taxonomic scale. Here, we used linear and angular dimensions to quantify symphysis shape. Using univariate, multivariate data...

We have described mandibular specimens of fossil colobines from the late Miocene site of Nakali (Kenya). Using qualitative and quantitative dental and mandibular traits, we compared them to an extensive sample of extant colobines and Miocene fossil colobines. We tested the hypothesis that i) only one species was present in this newly described foss...

The axial and appendicular skeleton of Japanese macaques (Macacca fuscata) trained to adopt bipedal posture and locomotion display a number of functionally related external and internal macro- and micromorphological changes, including site-specific cortical and trabecular bone adaptations. In this study we use high-resolution microtomography scanni...

Cainochoerus (Cainochoerinae) is a minute fossil suid (Mammalia, Artiodactyla, Suoidea) and its molar morphology recalls that of cercopithecoid primates. It is endemic to ca. 6.5–5 Ma of Africa. Here, we describe a new specimen of Cainochoerus discovered from the basal upper Miocene (ca. 10 Ma, Tortonian) Nakali Formation of central Kenya, East Afr...

The situation surrounding academic societies and research in Japan is getting more severe recently. We conducted a web-based survey for the members of the Anthropological Society of Nippon during August and September 2021 to obtain basic data for appropriately dealing with such a situation. Twenty-three percent of the members (n = 123) responded to...

Significance During human birth, the risk of complications is relatively high because of the comparatively large dimensions of the fetal head and shoulders relative to the maternal birth canal. Here we show that humans exhibit a developmental mode of the shoulders that likely contributes to mitigating obstetrical problems. Human shoulder growth is...

The size and morphology of male maxillary canines were compared among living/fossil apes, fossil hominins, and modern humans in the course of evolution. Results were summarized as follows: (1): The crown size of the upper canine had already reduced in the late Miocene hominins, such as Sahelanthropus tchadensis and Orrorin tugenensis. Then, size re...

The Colobines are a group of Afroeurasian monkeys that exhibit extraordinary behavioural and ecological diversity. With long tails and diverse colourations, they are medium-sized primates, mostly arboreal, that are found in many different habitats, from rain forests and mountain forests to mangroves and savannah. Over the last two decades, our unde...

Objectives Due to taphonomic processes, fossils have often undergone plastic deformation. To correctly assess the morphological affinities of such specimens, the original antemortem shape of the deformed specimens must be reconstructed. Here we describe a method to mathematically isolate and selectively eliminate the taphonomic deformation of a fos...

Significance Humans have the proportionately smallest male canines among all anthropoids and little canine sexual dimorphism. However, the evolutionary emergence of this defining condition remains unclear because until now we have lacked a reliable method of determining dimorphism in weakly dimorphic fossil species. Using a probability-based method...

Modern shark attacks are uncommon and archaeological examples are even rarer, with the oldest previously known case dating to ca. AD 1000. Here we report a shark attack on an adult male radiocarbon dated to 1370–1010 cal BC during the fisher-hunter-gatherer Jo ̄mon period of the Japanese archipelago. The individual was buried at the Tsukumo site ne...

Pliopithecoids are a diverse group of Miocene catarrhine primates from Eurasia. Their positional behavior is still unknown, and many species are known exclusively from dentognathic remains. Here, we describe a proximal radius (IPS66267) from the late Miocene of Castell de Barberà (Vallès-Penedès Basin, NE Iberian Peninsula) that represents the firs...

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 t...

Objectives: The little known guenon Cercopithecus dryas has a controversial taxonomic history with some recognizing two taxa (C. dryas and C. salongo) instead of one. New adult specimens from the TL2 region of the central Congo Basin allow further assessment of C. dryas morphology and, along with CT scans of the juvenile holotype, provide ontogene...

Reconstruction of the locomotor repertoire of the australopiths (Australopithecus and Paranthropus) has progressively integrated information from the mechanosensitive internal structure of the appendicular skeleton. Recent investigations showed that the arrangement of the trabecular network at the femoral head center is biomechanically compatible w...

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 is very fragmentary and is tentatively referred to the same species as the M2. The M2 specimen is assigned to the subfamily Schizotheriinae in having a cr...

Significance Reconstructing the phylogenetic relationships of extinct apes is challenging due to their fragmentary fossil record and the recurrent independent evolution of morphological features. Given the relevance of the phylogenetic signal of the bony labyrinth, here we assess the phylogenetic affinities of the late Miocene great apes Hispanopit...

Significance Childbirth is frequently difficult for humans due to a cephalocaudally short and dorsoventrally deep pelvis necessary for upright bipedality and a large neonatal brain. A tight fit between the neonatal head and maternal pelvic dimensions is, however, found not only in humans, but also in some other primate taxa. The rhesus macaques sho...

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. Materi...

Cane rats are represented by two extant species inhabiting Sub-Saharan Africa. Previous studies have established that the earliest occurrence of the extant genus Thryonomys was the latest Miocene in eastern Africa. A Japan-Kenya Expedition team has recovered a new species of Thryonomys, T. kamulai, sp. nov., from the base of the upper Miocene Nakal...

This article reports eight new humeral, ulnar, and radial fragments of Nacholapithecus kerioi collected from Nachola, Kenya during the 1998/1999 field seasons. The study refines the description of its forelimb bones, which was mostly based on a single partial skeleton. The most distinctive feature of the distal humerus is a large, globular, mediall...

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 propor...

Sesamoids of the metacarpophalangeal joint are tiny bones located in the volar plate and articulated with the metacarpal head. Almost all living humans have radial and ulnar sesamoids in their pollical metacarpophalangeal joints. These bones protect and guide the tendon of the long (= extrinsic) pollical flexor. Whereas this condition is considered...

The postcranial skeleton of living apes is characterized by a number of derived features that are attributable to the frequent forelimb-dominated orthograde positional behavior such as suspension or vertical climbing. Their axial skeletons exhibit a common specialization, e.g., a decreased number of lumbar vertebrae concomitant with an increase in...

Studies of the australopith (Australopithecus and Paranthropus) proximal femur have increasingly integrated information from the local arrangement of the cortical and cancellous bone to allow functional-biomechanical inferences on the locomotor behavioral patterns. In Australopithecus africanus and Para-nthropus robustus, the cancellous bone organi...

This paper provides a thorough description of humeral, ulnar, and radial specimens of the Nacholapithecus holotype (KNM-BG 35250). A spool-shaped humeral trochlea (and keeled sigmoid notch of the ulna) is a hallmark of elbow joint evolution in hominoids. In lacking this feature, the elbow of Nacholapithecus is comparatively primitive, resembling th...

SKX 1084 is an isolated partial patella from Swartkrans Member 2, South Africa, attributed to a small-bodied Paranthropus robustus. This study provides complementary information on its outer conformation and, for the first time for a fossil hominin patella, documents its inner structure in the perspective of adding biomechanically-related evidence...

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 her...

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 Nachol...

Inferring the morphology of the last common ancestor of humans, chimpanzees and gorillas is a matter of ongoing debate. Recent findings and reassessment of fossil hominins leads to the hypothesis that the last common ancestor was not extant African ape-like. However, an African great-ape-like ancestor with knuckle walking features still remains pla...

Epidemiological research has suggested that birth weights are correlated with adult leg lengths. However, the relationship between prenatal undernutrition (UN) and postnatal leg growth remains controversial. We investigated the effects of UN during early pregnancy on postnatal hindlimb growth and determined whether early embryonic malnutrition affe...

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...

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 Dic...

We here describe a prosimian specimen discovered from the early Middle Miocene (~15 Ma) of Nachola, northern Kenya. It is a right maxilla that preserves P⁴–M³, and is assigned to a new species of the Miocene lorisid genus Mioeuoticus. Previously, Mioeuoticus was known from the Early Miocene of East Africa. The Nachola specimen is therefore the firs...

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...

The African primate fossil record is very poor between the mid-Middle and mid-Late Miocene. Nakali (~10–9.8 Ma) is one of the rare African localities that have yielded primate fossils from this period, including a new genus of great ape, Nakalipithecus nakayamai, and another large-bodied hominoid species. The Nakali primate fauna also includes smal...

Please cite this article in press as:Chirchir, H., et al., Does trabecular bone structure within the metacarpal heads of primates vary with hand posture? C. R. Palevol (2016), http://dx. a b s t r a c t Reconstructing function from hominin fossils is complicated by disagreements over how to interpret primitively inherited, ape-like morphology. This...

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...

Hands of extant hominoids are highly derived compared with those of non-hominoid catarrhines. The evolution of the ape hand started from an appendage very well suited for powerful pollical-assisted grasping that supplied a balancing function in response to the loss of tail as seen in the early Miocene Proconsul (or Ekembo). Nacholapithecus from the...

Nakali is an early Late Miocene fossil locality in north-central Kenya, where the Kenya–Japan Joint Expedition team has carried out fieldwork since 2002. Previously, a large hominoid Nakalipithecus nakayamai was reported from site NA39 of this locality. In addition to Nakalipithecus, the hominoid material collected from Nakali includes an isolated...

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 specim...

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 describ...

This paper described crown morphology and sexual dimorphism of the canines in four species of the Great apes; Pongo pygmaeus, Gorilla gorilla, Pan trogrodytes, and Pan paniscus. At lingual view, the contours of maxillary canines in the males had an isosceles triangles with long mesial and distal incisal crests, while those of the females had an equ...

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...

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,...

Objective: Archaeological remains strongly suggest that the Holocene Japanese hunter-gatherers, the Jomon people, utilized terrestrial plants as their primary food source. However, carbon and nitrogen isotope analysis of bone collagen indicates that they primarily exploited marine resources. We hypothesize that this inconsistency stems from the ro...

New dental and astragalar specimens of a primitive hippopotamus, Kenyapotamus coryndonae (Mammalia, Cetartiodactyla, Hippopotamidae, Kenyapotaminae) from the lower Upper Miocene Nakali Formation at the Nakali locality, central Kenya, are described and illustrated. The new specimens increase the known morphological and size variations of the dentiti...

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 flattended lingual wall, a hypocone groove, a developed crochet, and an antecrochet curved toward the ent...

Proximal femoral morphology and associated musculature are of special relevance to the understanding of hominoid locomotor systems. Knowledge of bone–muscle correspondence in extant hominoids forms an important comparative basis for inferring structure–function relationships in fossil hominids. However, there is still a lack of consensus on the cor...

We analyzed the morphological variability of the cranial shape among the modern Japanese population using landmark-based geometric morphometrics. The sample comprised 56 cranial specimens of the modern Japanese population (23 female and 33 male) housed at Kyoto University. Computed tomography images of the crania were created and virtual models wer...

We apply the sliding semi-landmark method for the analysis of morphological variability in the modern Japanese population. Specifically, we prepare two kinds of template landmark configurations that will be projected onto and slid along each of the samples. We then analyze the variability in the neurocranial shape in the modern Japanese population...

Tooth crown patterning is governed by the growth and folding of the inner enamel epithelium (IEE) and the following enamel deposition forms outer enamel surface (OES). We hypothesized that overall dental crown shape and covariation structure are determined by processes that configurate shape at the enamel-dentine junction (EDJ), the developmental v...

Under the patterning cascade model (PCM) of cusp development inspired by developmental genetic studies, it is predicted that the location and the size of later-forming cusps are more variable than those of earlier-forming ones. Here we assessed whether differences in the variability among cusps in total and each particular crown component (enamel-d...

Anatomically-accurate interpolation of missing parts in fossil crania is important for correct estimation of brain morphology based on cranial shape information. In the present study, we attempted to establish a method to mathematically interpolate missing coordinates of crania based on a reference database of cranial morphology. Specifically, a to...

This study reconstructs linear enamel hypoplasia (LEH) prevalence and stress episode duration among Jomon period foragers from Hokkaido, Japan (HKJ). Results are compared to Jomon period samples from coastal Honshu, Japan (HSJ) and Tigara Inupiat from Point Hope, Alaska (PHT) to provide a more comprehensive perspective on the manifestation of stres...

Among the structural properties of trabecular bone, the degree of anisotropy is most often found to separate taxa with different habitual locomotor modes. This study examined the degree of anisotropy, the elongation, and primary orientation of trabecular bone in the KNM-ER 1464 Early Pleistocene hominin talus as compared with extant hominoid taxa....

Developmental prolongation is thought to contribute to the remarkable brain enlargement observed in modern humans (Homo sapiens). However, the developmental trajectories of cerebral tissues have not been explored in chimpanzees (Pan troglodytes), even though they are our closest living relatives. To address this lack of information, the development...

A gradual population increase accompanying climate cooling has been evinced as having occurred in western Japan during the Middle (ca. 5000–4000 years BP) to Late-Final Jomon period (ca. 4000–2300 years BP). We test the hypothesis that this population change paralleled increasing human migration. We also test the archaeological hypothesis that type...

We present the definitive description of the hind limb elements of the Nacholapithecus kerioi holotype (KNM-BG 35250) from the middle Miocene of Kenya. Previously, it has been noted that the postcranial (i.e. the phalanges, spine, and shoulder girdle) anatomy of N. kerioi shows greater affinity to other early/middle Miocene African hominoids, colle...

This paper describes the morphology of cervical vertebrae in Nacholapithecus kerioi, a middle Miocene primate species excavated from Nachola, Kenya in 1999-2002. The cervical vertebrae in Nacholapithecus are larger than those of Papio cynocephalus. They are more robust relative to more caudal vertebral bones. Since Nacholapithecus had large forelim...

We investigated the planar covariation of lower limb segment elevation angles during bipedal walking in macaques to elucidate the mechanisms underlying the origin and evolution of the planar law in human walking. Two Japanese macaques and four adult humans walking on a treadmill were recorded, and the time course of the elevation angles at the thig...

This study investigated interpopulation genetic relationships in the Jomon Atsumi Peninsula area, comparing the pattern of human migration revealed by strontium isotope ratio with dental metric variation of Yoshigo and Inariyama skeletal remains. Morphological differences were evaluated between the local and immigrant groups to determine whether or...

This review examined the hypothesis that a competition with the Cercopithecoidea accounts for the decline of the “Hominoidea” (properly speaking, non-cercopithecoid catarrhines on the present-day consensus of catarrhine taxonomy) from the beginning of the Miocene in Africa, originally put forward by P. Andrews (1981) [Species diversity and diet in...

The morphology of the talus prescribes relative positions and movements of the calcaneus and navicular with respect to the tibia, hence determining the overall geometry, mobility and function of the foot that mechanically interacts with environments. Clarifying the variations of the articular surface orientations of the talus in humans and extant g...

In animal walking, the gravitational potential and kinetic energy of the center of mass (COM) fluctuates out-of-phase to reduce the energetic cost of locomotion via an inverted pendulum mechanism, and, in canine quadrupedal walking, up to 70% of the mechanical energy can be recovered. However, the rate of energy recovery for quadrupedal walking in...

A comparison of developmental patterns of white matter (WM) within the prefrontal region between humans and nonhuman primates is key to understanding human brain evolution. WM mediates complex cognitive processes and has reciprocal connections with posterior processing regions [1 • Fuster J.M. Frontal lobe and cognitive development.J. Neurocytol....

Japanese macaques that have been trained for monkey performances exhibit a remarkable ability to walk bipedally. In this study, we dynamically reconstructed bipedal walking of the Japanese macaque to investigate causal relationships among limb kinematics, speed, and energetics, with a view to understanding the mechanisms underlying the evolution of...