Publications by authors named "Masato Nakatsukasa"

55 Publications

Three-dimensional orientations of talar articular surfaces in humans and great apes.

Primates 2011 Jan 16;52(1):61-8. Epub 2010 Sep 16.

Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Kyoto, Japan.

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 great apes is therefore of importance in understanding the evolution of bipedal locomotion in the human lineage. The aim of this study is to clarify the three-dimensional orientations of three articular surfaces of the talus (superior, posterior calcaneal and navicular articular surfaces) by means of the newly proposed surface approximation method. Thirty-two tali in humans, chimpanzees, gorillas and orangutans were scanned using a three-dimensional noncontact digitizer, and the articular surfaces were then approximated using a paraboloid or a plane to calculate the orientations of the surfaces with respect to the body of the talus. The results quantitatively demonstrated that the superior articular surfaces in humans were relatively more parallel with the horizontal plane of the talar body, while those in apes were more medially oriented. Furthermore, the cylindrical axis defined by the shape of the posterior calcaneal articular surface was directed less anteroposteriorly in humans than in apes, in contrast to the fact that the subtalar axis is more anteroposteriorly oriented in humans. It was also demonstrated that the navicular articular surface in humans was more plantarly oriented and axially twisted. These specialized features of the human talus seem to be functionally linked to obligate bipedal locomotion. The talar morphological differences among the great apes were prominent in the mediolateral and rotational orientations of the navicular articular surfaces, possibly reflecting the degree of arboreality among the great apes.
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http://dx.doi.org/10.1007/s10329-010-0219-1DOI Listing
January 2011

Three-dimensional musculoskeletal kinematics during bipedal locomotion in the Japanese macaque, reconstructed based on an anatomical model-matching method.

J Hum Evol 2010 Mar 8;58(3):252-61. Epub 2010 Jan 8.

Department of Mechanical Engineering, Faculty of Science and Technology, Keio University, Kohoku-ku, Yokohama, Japan.

Studying the bipedal locomotion of non-human primates is important for clarifying the evolution of habitual bipedalism in the human lineage. However, quantitative descriptions of three-dimensional kinematics of bipedal locomotion in non-human primates are very scarce, due to difficulties associated with measurements. In this study, we performed a kinematic analysis of bipedal locomotion on two highly trained (performing) Japanese macaques walking on a treadmill at different speeds and estimated three-dimensional angular motions of hindlimb and trunk segments, based on a model-based registration method. Our results demonstrated a considerable degree of axial rotation occurring at the trunk and hip joints during bipedal locomotion, suggesting that bipedal locomotion in Japanese macaques is essentially three-dimensional. In addition, ranges of angular motions at the hip and ankle joints were larger and the knee joint was more flexed in the mid-stance phase with increasing speed, indicating that gait kinematics are modulated depending on speed. Furthermore, macaques were confirmed to have actually acquired, at least to some extent, the energy conservation mechanism of walking due to pendular exchange of potential and kinetic energy, but effective utilization of this mutual exchange of energy was found to occur only at comparatively low velocity. Spring-like running mechanics were probably more exploited at higher speed because the duty factor was above 0.5. Fundamental differences in bipedal strategy seem to exist between human and non-human primate bipedal locomotion.
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http://dx.doi.org/10.1016/j.jhevol.2009.11.009DOI Listing
March 2010

Rib orientation and implications for orthograde positional behavior in nonhuman anthropoids.

Primates 2009 Oct 16;50(4):305-10. Epub 2009 Jun 16.

Laboratory of Physical Anthropology, Department of Zoology, Graduate School of Science, Kyoto University, Sakyo, Kyoto, Japan.

Strong caudal obliquity of the lower ribs is one of the assumed characteristics of the thoracic region in hominoids and Ateles. Strong caudal obliquity keeps the scapula of the weight-bearing forelimb on the dorsal surface of the trunk via the serratus anterior muscles during propulsion (Stern et al. 1980). We examined the orientation of odd-numbered ribs in lateral view in remounted thoracic skeletons of fifteen nonhuman anthropoids. Hominoids exhibit pronounced caudal obliquity in the seventh and ninth ribs compared to Old and New World monkeys. The position of the maximum thoracic cage width, which approximates the attachment of the serratus anterior muscle, is more caudally located in Hylobates and Pongo. The overall pattern of rib obliquity is generally similar between New and Old World monkeys, including Ateles. Perhaps not only forelimb suspensory behavior but also various orthograde positional behaviors are related to the strong obliquity of the lower ribs; however, further investigation is necessary.
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http://dx.doi.org/10.1007/s10329-009-0147-0DOI Listing
October 2009

Development of an anatomically based whole-body musculoskeletal model of the Japanese macaque (Macaca fuscata).

Am J Phys Anthropol 2009 Jul;139(3):323-38

Laboratory of Physical Anthropology, Department of Zoology, Graduate School of Science, Kyoto University, Kitashirakawa-oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan.

We constructed a three-dimensional whole-body musculoskeletal model of the Japanese macaque (Macaca fuscata) based on computed tomography and dissection of a cadaver. The skeleton was modeled as a chain of 20 bone segments connected by joints. Joint centers and rotational axes were estimated by joint morphology based on joint surface approximation using a quadric function. The path of each muscle was defined by a line segment connecting origin to insertion through an intermediary point if necessary. Mass and fascicle length of each were systematically recorded to calculate physiological cross-sectional area to estimate the capacity of each muscle to generate force. Using this anatomically accurate model, muscle moment arms and force vectors generated by individual limb muscles at the foot and hand were calculated to computationally predict muscle functions. Furthermore, three-dimensional whole-body musculoskeletal kinematics of the Japanese macaque was reconstructed from ordinary video sequences based on this model and a model-based matching technique. The results showed that the proposed model can successfully reconstruct and visualize anatomically reasonable, natural musculoskeletal motion of the Japanese macaque during quadrupedal/bipedal locomotion, demonstrating the validity and efficacy of the constructed musculoskeletal model. The present biologically relevant model may serve as a useful tool for comprehensive understanding of the design principles of the musculoskeletal system and the control mechanisms for locomotion in the Japanese macaque and other primates.
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http://dx.doi.org/10.1002/ajpa.20986DOI Listing
July 2009

Comparative study of Moroto vertebral specimens.

J Hum Evol 2008 Oct 31;55(4):581-8. Epub 2008 Jul 31.

Laboratory of Physical Anthropology, Kyoto University, Sakyo, Kyoto 606-8502, Japan.

The hypodigm of Morotopithecus bishopi includes several vertebral specimens from Moroto II in addition to a scapular fragment, and femoral and craniodental specimens. The Moroto vertebral specimens include UMP 67.28, which is a well-preserved lumbar vertebra. Based on the derived morphological traits in UMP 67.28, together with evidence from other postcranial elements, it has been claimed that certain aspects of the modern hominoid body plan appeared in the hominoid lineage by as early as 20Ma. Other vertebral specimens from the site are not well-preserved and have not been described in detail. This article provides the first detailed description of these specimen with an emphasis on a lumbar vertebral body UMP 68.06. Results confirm the existing interpretations that M. bishopi had a more dorsostable lumbar column compared to other African Miocene hominoids, such as Proconsul nyanzae/heseloni or Nacholapithecus kerioi. The vertebral body is craniocaudally short and the median ventral keel is absent through the lumbar column. However, M. bishopi might have had a similar number segments as inferred for P. nyanzae (6-7) if UMP 68.06 and UMP 67.28 are associated. Likewise, the ventral wedging of UMP 68.06 may suggest that M. bishopi had more lumbar vertebrae than extant great apes. The origin of the transverse process relative to the vertebral body is variable by level among the Moroto specimens. Thus, if these specimens derive from a single taxon, this may suggest considerable variability in this feature that would advise caution when using this feature to draw taxonomic or functional conclusions.
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http://dx.doi.org/10.1016/j.jhevol.2008.04.009DOI Listing
October 2008

Variation in limb proportions between Jomon foragers and Yayoi agriculturalists from prehistoric Japan.

Am J Phys Anthropol 2008 Oct;137(2):164-74

Department of Anthropology, The Ohio State University, Columbus, OH 43210-1364, USA.

Variation in limb proportions between prehistoric Jomon and Yayoi people of Japan are explored by this study. Jomon people were the descendents of Pleistocene nomads who migrated to the Japanese Islands around 30,000 yBP. Phenotypic and genotypic evidence indicates that Yayoi people were recent migrants to Japan from continental Northeast Asia who likely interbred with Jomon foragers. Limb proportions of Jomon and Yayoi people were compared using RMA regression and "Quick-Test" calculations to investigate relative variability between these two groups. Cluster and principal components analyses were performed on size-standardized limb lengths and used to compare Jomon and Yayoi people with other groups from various climatic zones. Elongated distal relative to proximal limb lengths were observed among Jomon compared to Yayoi people. Jomon limb proportions were similar to human groups from temperate/tropical climates at lower latitudes, while Yayoi limb proportions more closely resemble groups from colder climates at higher latitudes. Limb proportional similarities with groups from warmer environments among Jomon foragers likely reflect morphological changes following Pleistocene colonization of the Japanese Islands. Cold-derived limb proportions among the Yayoi people likely indicate retention of these traits following comparatively recent migrations to the Japanese Islands. Changes in limb proportions experienced by Jomon foragers and retention of cold-derived limb proportions among Yayoi people conform to previous findings that report changes in these proportions following long-standing evolution in a specific environment.
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http://dx.doi.org/10.1002/ajpa.20853DOI Listing
October 2008

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

Proc Natl Acad Sci U S A 2007 Dec 16;104(49):19220-5. Epub 2007 Nov 16.

Primate Research Institute, Kyoto University, Aichi 484-8506, Japan.

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.
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http://dx.doi.org/10.1073/pnas.0706190104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2148271PMC
December 2007

Morphological study of the anthropoid thoracic cage: scaling of thoracic width and an analysis of rib curvature.

Primates 2008 Apr 28;49(2):89-99. Epub 2007 Sep 28.

Laboratory of Physical Anthropology, Department of Zoology, Graduate School of Science, Kyoto University, Sakyo, Kyoto, 606-8502, Japan.

While a relatively broad thorax and strongly curved ribs are widely regarded as common features of living hominoids, few studies have quantitatively examined these traits by methods other than calculating the chest index. The present study aims to quantify variations in thoracic cage morphology for living anthropoids. The odd-numbered ribs (first to eleventh) were articulated with the corresponding vertebrae and the cranial and lateral views subsequently photographed. Rib profiles were digitized in both views and line-fitted by a Bézier curve to create a three-dimensional morphological data set. When thoracic cage width was scaled against body mass, Hylobates (and possibly Pongo) plotted above non-hominoid anthropoids at almost all rib levels, while Pan did not differ from non-hominoid anthropoids. The overall pattern of the normalized thoracic width differed between Hylobates and other hominoids. In Hylobates, an upward convex curve was seen between the first and seventh ribs while a more linear pattern was observed in Pan and Pongo. This result quantitatively confirmed that the barrel-shaped thoracic cage in Hylobates can be distinguished from the funnel-shaped form in other hominoids. Conversely, all hominoids shared two distinct features in the upper half-thorax: (1) a pronounced dorsal protrusion of the proximal part of the rib in accordance with ventral displacement of the thoracic spine and (2) a relatively medially projecting sternal end. Although these features are likely to provide some mechanical advantage in orthograde and/or suspensory positional behaviors, they were barely present in the suspensory Ateles.
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http://dx.doi.org/10.1007/s10329-007-0064-zDOI Listing
April 2008

Textural characteristics of the iliac-femoral trabecular pattern in a bipedally trained Japanese macaque.

Primates 2008 Jan 14;49(1):16-25. Epub 2007 Jul 14.

Laboratoire de Planétologie et Géodynamique, UMR CNRS 6112, Université de Nantes, 2 rue de la Houssinière, BP 92208, 44322 Nantes Cedex 3, France.

Previous research has revealed that Japanese macaques (Macaca fuscata) trained in bipedal performance (Saru-mawashi) display a number of functionally related external skeletal changes, as well as some site-specific endostructural cortical and cancellous adaptations. Through radiography assisted by digital image processing, we investigated the trabecular pattern of the ilium and femoral neck of Sansuke, a macaque habitually bipedally trained for 8 years. A set of eight regions of interest on Sansuke were recorded for subtle structural characterization of the cancellous network and compared to a sample of 5 ilia and 23 femurs from 26 adult wild Japanese macaques. The measured variables include trabecular thickness, trabecular bone volume, and degree of anisotropy. As a whole, the site-specific textural characteristics of the cancellous network detected on the ilium and proximal femur of the bipedally trained macaque can be interpreted as functional adaptive responses to more compressive loads dissipated along the axis from the sacro-iliac to the coxo-femoral joint, and back.
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http://dx.doi.org/10.1007/s10329-007-0053-2DOI Listing
January 2008

Ground-reaction-force profiles of bipedal walking in bipedally trained Japanese monkeys.

J Hum Evol 2007 Sep 14;53(3):302-8. Epub 2007 Jun 14.

Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan.

Ground-reaction-force (GRF) profiles of bipedal locomotion in bipedally trained Japanese macaques (performing monkeys) were analyzed in order to clarify the dynamic characteristics of their locomotion. Five trained and two ordinary monkeys participated in the experiment. They walked on a wooden walkway at a self-selected speed, and three components of the GRF vector were measured using a force platform. Our measurements reveal that trained monkeys exhibited vertical-GRF profiles that were single-peaked, similar to those of ordinary monkeys; they did not generate the double-peaked force curve that is seen in humans, despite their extensive training. However, in the trained monkeys, the peak appeared relatively earlier in the stance phase, and overall shape was more triangular than that of the more parabolic profile generated by ordinary monkeys. Comparisons of vertical fluctuation of the center of body mass calculated from the measured profiles suggest that this was larger in the trained monkeys, indicating that storage and release of potential energy actually took place in their bipedal walking. This energetic advantage seems limited, however, because efficient exchange of potential and kinetic energy during walking were not completely out of phase as in human walking. We suggest that anatomically restricted range of hip-joint motion impedes the inherently quadrupedal monkeys from generating humanlike bipedal locomotion, and that morphological rearrangement of the hip joint was an essential precondition for protohominids to acquire humanlike bipedalism.
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http://dx.doi.org/10.1016/j.jhevol.2007.04.004DOI Listing
September 2007

Vertebral morphology of Nacholapithecus kerioi based on KNM-BG 35250.

J Hum Evol 2007 Apr 14;52(4):347-69. Epub 2006 Sep 14.

Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Kyoto 6068502, Japan.

This paper describes the morphology of the vertebral remains of the KNM-BG 35250 Nacholapithecus kerioi individual from the Middle Miocene of Kenya. Cervical vertebrae are generally large relative to presumed body mass, suggesting a heavy head with large jaws and well-developed neck muscles. The atlas retains the lateral and posterior bridges over the vertebral artery. The axis has a robust dens and a large angle formed by superior articular surfaces. The thoracic vertebral specimens include the diaphragmatic vertebra and one post-diaphragmatic vertebra. The thoracic vertebral bodies are much smaller that those of male Papio cynocephalus, whereas many of the dorsal elements are large and robust, exceeding those of male P. cynocephalus. Lumbar vertebral bodies are small relative to body mass, craniocaudally moderately long, and have a median ventral keel. The transverse process is craniocaudally long and arises from the widest part of the body cranially and the pedicle above the inferior vertebral notch caudally. Anapophyses are present in one of the preserved lumbar vertebrae. The postzygapophyses are thick dorsoventrally. These lumbar features are broadly shared with Proconsul. However, the base of the spinous process is longer and more caudally positioned in N. kerioi compared to Proconsul, and is more similar to the condition in Pongo. They are not dorsally (or moderately caudally) directed as is seen in P. nyanzae, Pan, and most other extant primates. A caudally directed spinous process does not permit a broad range of spinal dorsiflexion. The presumed stiff back in N. kerioi suggests a different locomotor repertoire than in Proconsul. Morotopithecus bishopi, although not possessing the same features, exhibits another morphological suite of characters for lumbar stiffness. Diverse functional adaptations of the lumbar spine were present in African hominoids during the Early to Middle Miocene.
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http://dx.doi.org/10.1016/j.jhevol.2006.08.008DOI Listing
April 2007

Femur length, body mass, and stature estimates of Orrorin tugenensis, a 6 Ma hominid from Kenya.

Primates 2007 Jul 22;48(3):171-8. Epub 2007 Feb 22.

Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Sakyo, Kyoto, 606-8502, Japan.

To understand the palaeobiology of extinct hominids it is useful to estimate their body mass and stature. Although many species of early hominid are poorly preserved, it is occasionally possible to calculate these characteristics by comparison with different extant groups, by use of regression analysis. Calculated body masses and stature determined using these models can then be compared. This approach has been applied to 6 Ma hominid femoral remains from the Tugen Hills, Kenya, attributed to Orrorin tugenensis. It is suggested that the best-preserved young adult individual probably weighed approximately 35-50 kg. Another fragmentary femur results in larger estimates of body mass, indicative of individual variation. The length of the femur of the young adult individual was estimated, by using anthropoid-based regression, to be a minimum of 298 mm. Because whole-femur proportions for Orrorin are unknown, this prediction is conservative and should be revised when additional specimens become available. When this predicted value was used for regression analysis of bonobos and humans it was estimated to be 1.1-1.2 m tall. This value should, however, be viewed as a lower limit.
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http://dx.doi.org/10.1007/s10329-007-0040-7DOI Listing
July 2007

Computerized restoration of nonhomogeneous deformation of a fossil cranium based on bilateral symmetry.

Am J Phys Anthropol 2006 May;130(1):1-9

Laboratory of Physical Anthropology, Department of Zoology, Graduate School of Science, Kyoto University, Kitashirakawa-oiwakecho, Kyoto 606-8502, Japan.

We developed a computerized method of correcting plastic deformation of a fossil skull, based on bilateral symmetry with respect to the midsagittal plane, and applied this method to reconstruction of a fossilized Proconsul heseloni cranium (KNM-RU-7290A). A three-dimensional (3D) model of the fossil was generated using consecutive cross-sectional images retrieved from computed tomography. 3D coordinates of anatomical landmarks that should be located on the midsagittal plane and pairs of landmarks that should be symmetrical with respect to this plane were acquired. These landmarks were then repositioned so that geometrical constraints were satisfied, while translated distances of landmarks were minimized. We adopted a thin-plate spline function to mathematically describe the 3D nonlinear volumetric transformation between acquired and repositioned landmarks. Using this function, the entire fossil shape was transformed, and the effect of reversing the deformation could be visualized. The results indicated that the proposed method was effective in eliminating nonhomogeneous deformation of the fossil skull. The antemortem appearance of the skull cannot be completely restored by this method alone, due to methodological limitations. However, the presented method has a role as an adjunct in complementing conventional restoration techniques on account of its objective nature.
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http://dx.doi.org/10.1002/ajpa.20332DOI Listing
May 2006

Muscle dimensions in the chimpanzee hand.

Primates 2005 Oct 6;46(4):275-80. Epub 2005 Sep 6.

Laboratory of Physical Anthropology, Department of Zoology, Graduate School of Science, Kyoto University, Sakyo, Kyoto, Japan.

We dissected the forearms and hands of a female chimpanzee and systematically recorded mass, fiber length, and physiological cross-sectional area (PCSA) of all muscles including those of intrinsic muscles that have not been reported previously. The consistency of our measurements was confirmed by comparison with the published data on chimpanzees. Comparisons of the hand musculature of the measured chimpanzee with corresponding published human data indicated that the chimpanzee has relatively larger forearm flexors but smaller thenar eminence muscles, as observed in previous studies. The interosseous muscles were also confirmed to be relatively larger in the chimpanzee. However, a new finding was that relative PCSA, which reflects a muscle's capacity to generate force, might have increased slightly in humans as a result of relatively shorter muscle fiber length. This suggests that the human intrinsic muscle architecture is relatively more adapted to dexterous manipulative functions. Shortening of the metacarpals and the intervening interosseous muscles might accordingly be a prerequisite for the evolution of human precision-grip capabilities.
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http://dx.doi.org/10.1007/s10329-005-0136-xDOI Listing
October 2005

Kinematic analysis of bipedal locomotion of a Japanese macaque that lost its forearms due to congenital malformation.

Primates 2005 Jan 6;46(1):11-9. Epub 2004 Aug 6.

Laboratory of Physical Anthropology, Department of Zoology, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan.

Spontaneously acquired bipedal locomotion of an untrained Japanese monkey (Macaca fuscata) is measured and compared with the elaborated bipedal locomotion of highly trained monkeys to assess the natural ability of a quadrupedal primate to walk bipedally. The subject acquired bipedalism by himself because of the loss of his forearms and hands due to congenital malformation. Two other subjects are performing monkeys that have been extensively trained for bipedal posture and locomotion. We videotaped their bipedal locomotion with two cameras in a lateral view and calculated joint angles (hip, knee, and ankle) and inertial angle of the trunk from the digitized joint positions. The results show that all joints are relatively more flexed in the untrained monkey. Moreover, it is noted that the ankle is less plantar flexed and the knee is more flexed in mid-to-late stance phase in the untrained monkey, suggesting that the trunk is not lifted up to store potential energy. In the trained monkeys, the joints are extended to bring the trunk as high as possible in the stance phase, and then stored potential energy is exchanged for kinetic energy to move forward. The efficient inverted pendulum mechanism seems to be absent in the untrained monkey's locomotion, implying that acquisition of such efficient bipedal locomotion is not a spontaneous ability for a Japanese monkey. Rather, it is probably a special skill that can only be acquired through artificial training for an inherently quadrupedal primate.
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http://dx.doi.org/10.1007/s10329-004-0100-1DOI Listing
January 2005

Acquisition of bipedalism: the Miocene hominoid record and modern analogues for bipedal protohominids.

J Anat 2004 May;204(5):385-402

Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Japan.

The well-known fossil hominoid Proconsul from the Early Miocene of Kenya was a non-specialized arboreal quadruped with strong pollicial/hallucial assisted grasping capability. It lacked most of the suspensory specializations acquired in living hominoids. Nacholapithecus, however, from the Middle Miocene of Kenya, although in part sharing with Proconsul the common primitive anatomical body design, was more specialized for orthograde climbing, 'hoisting' and bridging, with the glenoid fossae of the scapula probably being cranially orientated, the forelimbs proportionally large, and very long toes. Its tail loss suggests relatively slow movement, although tail loss may already have occurred in Proconsul. Nacholapithecus-like positional behaviour might thus have been a basis for development of more suspensory specialized positional behaviour in later hominoids. Unfortunately, after 13 Ma, there is a gap in the hominoid postcranial record in Africa until 6 Ma. Due to this gap, a scenario for later locomotor evolution prior to the divergence of Homo and Pan cannot be determined with certainty. The time gap also causes difficulties when we seek to determine polarities of morphological traits in very early hominids. Interpretation of the form-function relationships of postcranial features in incipient hominids will be difficult because it is predicted that they had incorporated bipedalism only moderately into their total positional repertoires. However, Japanese macaques, which are trained in traditional bipedal performance, may provide useful hints about bipedal adaptation in the protohominids. Kinematic analyses revealed that these macaques walked bipedally with a longer stride and lower stride frequency than used by ordinary macaques, owing to a more extended posture of the hindlimb joints. The body centre of gravity rises during the single-support phase of stance. Energetic studies of locomotion in these bipedal macaques revealed that energetic expenditure was 20-30% higher in bipedalism than in quadrupedalism, regardless of walking velocity.
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http://dx.doi.org/10.1111/j.0021-8782.2004.00290.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1571308PMC
May 2004

Do highly trained monkeys walk like humans? A kinematic study of bipedal locomotion in bipedally trained Japanese macaques.

J Hum Evol 2004 Jun;46(6):739-50

Laboratory of Biological Anthropology, Graduate School of Human Sciences, Osaka University, Suita, Osaka 5650871, Japan.

In this study, we examined the kinematics of bipedal walking in macaque monkeys that have been highly trained to stand and walk bipedally, and compared them to the kinematics of bipedal walking in ordinary macaques. The results revealed that the trained macaques walked with longer and less frequent strides than ordinary subjects. In addition, they appear to have used inverted pendulum mechanics during bipedal walking, which resulted in an efficient exchange of potential and kinetic energy. These gait characteristics resulted from the relatively more extended hindlimb joints of the trained macaques. By contrast, the body of the ordinary macaques translated downward during the single-limb stance phase due to more flexed hindlimb joints. This resulted in almost in-phase fluctuations of potential and kinetic energy, which indicated that energy transformation was less efficient in the ordinary macaques. The findings provide two insights into the early stage of the evolution of human bipedalism. First, the finding that training considerably improved bipedal walking a posteriori may explain why the very first bipeds that might not yet have been morphologically adapted to bipedal walking continued to walk bipedally. The evolutionary transition from quadrupedalism to bipedalism might not be as difficult as has been envisioned. In addition, the finding that macaques, which are phylogenetically distant from humans and in which bipedal walking is unlike human walking, could develop humanlike gait characteristics with training, provides strong support for the commonly held but unproven idea that the characteristics of the human gait are advantageous to human bipedalism.
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http://dx.doi.org/10.1016/j.jhevol.2004.04.004DOI Listing
June 2004

Maxillae and associated gnathodental specimens of Nacholapithecus kerioi, a large-bodied hominoid from Nachola, northern Kenya.

J Hum Evol 2004 Apr;46(4):365-400

Primate Research Institute, Kyôto University, Kanrin, Inuyama, Aichi, 484-8506, Japan.

The middle Miocene large-bodied hominoid from Nachola, initially attributed to Kenyapithecus, was recently transferred to a new genus and species Nacholapithecus kerioi. The hypodigm of N. kerioi consists of numerous maxillae, mandibles, and isolated teeth, as well as a number of postcranial bones. A detailed description of the previously discovered postcranial material has already been presented. This article aims to give a detailed description of maxillary specimens (including some mandibular fragments associated with them) of N. kerioi collected by the Japan-Kenya Joint Project team during the field seasons of 1982, 1984, and 1986. The maxillary specimens of N. kerioi retain a set of primitive catarrhine features, such as a relatively shallow palate, low position of the anterior zygomatic root, and the lack of enlarged premolars. Yet, compared to the Early Miocene Proconsul, N. kerioi is derived in having a moderately elongated subnasal clivus that appears to have overlapped the hard palate.
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http://dx.doi.org/10.1016/j.jhevol.2003.12.008DOI Listing
April 2004

Preliminary analysis of Nacholapithecus scapula and clavicle from Nachola, Kenya.

Primates 2004 Apr 9;45(2):97-104. Epub 2004 Mar 9.

Département d'Histoire de la Terre du Muséum National d'Histoire Naturelle, UMR 5143 et PICS 1048, CNRS, 8, rue Buffon, 75005 Paris, France.

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.
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http://dx.doi.org/10.1007/s10329-003-0073-5DOI Listing
April 2004

Nacholapithecus skeleton from the Middle Miocene of Kenya.

J Hum Evol 2004 Jan;46(1):69-103

Department of Human Nursing, University of Shiga Prefecture, Hikone, Shiga 5228533, Japan.

An almost entire skeleton of a male individual of Nacholapithecus kerioi (KNM-BG 35250) was discovered from Middle Miocene (approximately 15 Ma) sediments at Nachola, northern Kenya. N. kerioi exhibits a shared derived subnasal morphology with living apes. In many postcranial features, such as articular shape, as well as the number of the lumbar vertebrae, N. kerioi resembles Proconsul heseloni and/or P. nyanzae, and lacks suspensory specializations characteristic of living apes. Similarly, N. kerioi shares some postcranial characters with Kenyapithecus spp. However, despite the resemblance, N. kerioi and Proconsul spp. are quite different in their body proportions and some joint morphologies. N. kerioi has proportionally large forelimb bones and long pedal digits compared to its hindlimb bones and lumbar vertebrae. Its distinctive body proportions suggest that N. kerioi was more derived for forelimb dominated arboreal activities than P. nyanzae and P. heseloni. On the other hand, it exhibits a mixture of derived and primitive cranio-dental and postcranial features relative to the contemporaneous Kenyapithecus and Early MioceneMorotopithecus. While the phylogenetic position of N. kerioi is unsettled, it seems necessary to posit parallel evolution of cranio-dental and/or postcranial features in fossil and living apes.
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http://dx.doi.org/10.1016/j.jhevol.2003.10.001DOI Listing
January 2004

Comparative and functional anatomy of phalanges in Nacholapithecus kerioi, a Middle Miocene hominoid from northern Kenya.

Primates 2003 Oct 24;44(4):371-412. Epub 2003 Sep 24.

Laboratory of Physical Anthropology, Kyoto University, Sakyo, Kyoto 606-8502, Japan.

We describe phalanges of the KNM-BG 35250 Nacholapithecus kerioi skeleton from the Middle Miocene of Kenya. Phalanges of N. kerioi display similarities to those of Proconsul heseloni despite their enhanced robusticity. They do not show highly specialized features as in living suspensory primates. However, N. kerioi manifests several distinctive features that are observed in neither living arboreal quadrupeds nor P. heseloni or P. nyanzae. The most remarkable of them is its phalangeal elongation. N. kerioi phalanges (particularly pedal) are as long as those of Pan despite its much smaller body size. While lengthened digits enable a secure grip of supports and are especially adaptive for grasping large vertical trunks, the skeletal and soft tissues are subjected to greater stress. Probably, strong selective pressures favored powerful hallucal/pollical assisted grips. Although this functional adaptation does not exclude the possible use of the terrestrial environment, arboreal behavioral modes must have been crucial in its positional repertoire. N. kerioi is distinguished from P. heseloni in the greater size of its manual phalanges over its pedal phalanges. These derived features of N. kerioi suggest positional modes supporting more weight on the forelimb, and which occur more frequently on vertical supports. If Proconsul is referred to as an "above-branch arboreal quadruped" with a deliberate and effective climbing capability, N. kerioi may be thought of as an "orthograde climber". While living apes are powerful orthograde climbers, they are also more or less suspensory specialists. Suspensory behavior (plus climbing) and pronograde quadrupedalism (plus climbing) are the two main arboreal behavioral adaptations in living anthropoids. Thus, N. kerioi is an unusual fossil primate in that it cannot be incorporated into this dichotomy. It is plausible that a N. kerioi-like orthograde climber with large forelimbs and cheiridia was a precursor of suspensory living apes, and N. kerioi may demonstrate what an initial hominoid of this grade might have looked like.
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http://dx.doi.org/10.1007/s10329-003-0051-yDOI Listing
October 2003

Scaling of lumbar vertebrae in anthropoids and implications for evolution of the hominoid axial skeleton.

Primates 2003 Apr 19;44(2):127-35. Epub 2003 Feb 19.

Laboratory of Physical Anthropology, Department of Zoology, Graduate School of Science, Kyoto University, Kyoto 606-8502, Sakyo, Japan.

We investigated allometric relationships between vertebral centrum cranial surface areas and body weight and skeletal lumbar length in extant platyrrhine and cercopithecid species. Platyrrhines have smaller lumbar vertebral centra regarding the cranial surface area relative to their body weight than extant catarrhines. However, the stress to the spine of quadrupeds is not only influenced by the body weight but also its length, which contributes to the amount of bending moment. Our results indicated that platyrrhines and cercopithecids have similar lumbar vertebral centrum surface areas when they are scaled on the product of the body weight and skeletal lumbar length. Platyrrhines generally tend to have relatively short lumbar columns for a given body weight. As a result of this tendency, their vertebral centra appear relatively small if only body weight is taken into account. The centrum surface area is rather constant relative to the product of the body weight and skeletal lumbar length within platyrrhines or cercopithecids, despite the fact that skeletal lumbar length is in itself rather variable relative to body weight. This result indicates that the vertebral centrum articular area, the lumbar column length and the body weight are strongly correlated with each other and that such relationships are similar between platyrrhines and cercopithecids. These relationships were observed using both the zygapophyseal and rib definitions of the lumbar vertebrae. However, they were more clearly observed when the zygapophyseal definition was adopted. It appeared that lumbar vertebrae of Proconsul nyanzae (KNM-MW 13142) had distinctively smaller surface areas relative to its body weight and lumbar length than for platyrrhines and cercopithecids, differing from extant hominoids, which have comparatively larger lumbar vertebrae. In the case of Morotopithecus, the lumbar vertebral surface area seems to be as large as in extant platyrrhines and cercopithecids if it had a reduced number of lumbar vertebrae. It is uncertain whether its lumbar vertebral surface area was as large as in extant hominoids.
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http://dx.doi.org/10.1007/s10329-002-0010-zDOI Listing
April 2003

Morphology of the hallucial phalanges in extant anthropoids and fossil hominoids.

Z Morphol Anthropol 2002 Mar;83(2-3):361-72

Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Sakyo, Kyoto, Japan.

Pedal phalanges of living anthropoids and several Miocene fossil hominoid taxa were studied to reveal functional adaptations of living anthropoid feet and to infer positional behavior of fossil hominoids. Among the examined living anthropoids, Pan has a very developed (long and robust) hallux. Proconsul and Nacholapithecus, a large hominoid from Nachola, northern Kenya, display a moderately long hallux like Alouatta and Cebus, suggesting the well-developed capability of a hallux-assisted power grip. Allometric analyses revealed that the Miocene hominoids examined (mainly from East Africa) as a whole displayed a different scaling pattern about the width of the proximal articular surface of the hallucial terminal phalanx from that of living anthropoids. Larger-sized hominoids display a wider articular surface than comparable-sized living anthropoids while smaller-sized fossil hominoids do the reverse. Such a difference was less marked for the height of the articular surface. These results may suggest that positional adaptations of Miocene hominoids are not merely resultants of a common body size function that is observed in living anthropods. The wide articular surface of fossil hominoid hallucial terminal phalanges suggests an adaptation for vertical climbing and clinging, in which the hallux is kept perpendicularly to the long axis of the vertical support.
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March 2002