<Cranial thoracic vertebra of Nacholapithecus> 2025

The thoracic vertebra from the cranial series of Nacholapithecus kerioi has a unique set of characteristics. The major characteristics observed are dorsally positioned (in relation to the vertebral body) and dorsolaterally oriented transverse process, suggesting a weak spinal invagination and a long transverse process. As a whole, this thoracic vertebra sheds light on a new aspect of the spinal anatomy of N. kerioi.

Kikuchi Y, Amano H, Ogihara N, Nakatsukasa M, Nakano Y, Shimizu D, Kunimatsu Y, Tsujikawa H, Takano T, Ishida H.  

Retrodeformation and functional anatomy of a cranial thoracic vertebra in Nacholapithecus kerioi.

Journal of Human Evolution, 198: 103613

https://doi.org/10.1016/j.jhevol.2024.103613

<Sexual dimorphism of Nacholapithecus> 2018

This study examined body mass sexual dimorphism in Nacholapithecus kerioi, finding it comparable to that of Gorilla, with males about twice the size of females. Unlike Gorilla or Pongo, however, the high dimorphism may not reflect similar mating systems, possibly due to taphonomic bias or different social structures. Fossil apes may have had more diverse mating systems than extant hominoids.

Kikuchi Y, Nakatsukasa M, Tsujikawa H, Nakano Y, Kunimatsu Y, Shimizu D, Ogihara N, Takano T, Nakaya H, Sawada Y, Ishida H. 

Journal of Human Evolution, 123: 129-140. 

https://doi.org/10.1016/j.jhevol.2018.07.003 

<Sacral vertebral remains of Nacholapithecus> 2016

Two new sacral specimens of Nacholapithecus kerioi suggest it had a small lumbosacral articular surface relative to body mass, similar to great apes and Proconsul. The sacrum shows a high craniocaudal vertebral body reduction (CVR), resembling Old World monkeys, which typically have three sacral vertebrae. This raises the possibility that N. kerioi also had only three sacral vertebrae, indicating a primitive or transitional sacral morphology.

Kikuchi Y, Nakatsukasa M, Nakano Y, Kunimatsu Y, Shimizu D, Ogihara N, Tsujikawa H, Takano T, Ishida H.  

Journal of Human Evolution, 94: 117-125. 

 https://doi.org/10.1016/j.jhevol.2016.03.006 

<Thoracolumbar spine of Nacholapithecus> 2015

New thoracic and lumbar vertebrae of Nacholapithecus kerioi show features similar to extant great apes, including craniocaudally expanded, caudally directed spinous processes and non-projecting postzygapophyses. These traits enhance vertebral stability and suggest antipronograde behaviors. Unlike extant apes, N. kerioi had at least two post-diaphragmatic vertebrae. Overall, the vertebral morphology supports a combination of arboreal quadrupedalism and upright postural behaviors.

Kikuchi Y, Nakatsukasa M, Nakano Y, Kunimatsu Y, Shimizu D, Ogihara N, Tsujikawa H, Takano T, Ishida H.

Journal of Human Evolution, 88: 25-42. 

https://doi.org/10.1016/j.jhevol.2015.09.003

<Cervical vertebrae of Nacholapithecus> 2012

The cervical vertebrae of Nacholapithecus kerioi are robust and large, likely supporting strong forelimb use. While some features are primitive, others—like the atlas and axis morphology—show similarities to extant great apes, suggesting incipient orthograde adaptations. These mixed traits imply that N. kerioi was beginning to specialize toward the upright posture and locomotor behaviors seen in modern hominoids.

Kikuchi Y, Nakano Y, Nakatsukasa M, Kunimatsu Y, Shimizu D, Ogihara N, Tsujikawa H, Takano T, Ishida H.  

Journal of Human Evolution, 62: 677-695. 

https://doi.org/10.1016/j.jhevol.2012.03.002 

<Functional anatomy and adaptation of the third to sixth thoracic vertebrae in primates using three‑dimensional geometric morphometrics> 2021

This study analyzed the 3rd to 6th thoracic vertebrae of various primates, revealing that hominoids have more dorsally positioned transverse processes than monkeys, contributing to greater dorsal vertebral depth. Vertebral shapes reflect locomotor behavior more than phylogeny; for example, the suspensory Ateles and arboreal Nasalis share similar vertebral features despite distant relations, highlighting functional adaptation in thoracic morphology.

Kikuchi Y, Ogihara N.  

Functional anatomy and adaptation of the third to sixth thoracic vertebrae in primates using three‑dimensional geometric morphometrics

Primates, 62: 845-855. 

https://doi.org/10.1007/s10329-021-00929-3 

<Sexual Dimorphism of Endocranial, Facial and Limb Measurements in the Yellow Baboon (Papio cynocephalus> 2015

In yellow baboons (Papio cynocephalus), sexual dimorphism is most pronounced in palate length and least in endocranial volume. Males tend to have longer, more pointed muzzles enhancing canine display for social signaling and male competition, rather than larger facial size linked to body size or diet. Most facial and body measurements show weak allometric scaling with body mass, highlighting the role of sexual selection in shaping dimorphic traits.

Kikuchi Y, Kuraoka A. 

Anatomia Histologia Embryologia, 44: 275-282. 

https://doi.org/10.1111/ahe.12136 

<Relationship between humeral geometry and shoulder muscle power among suspensory, knuckle-walking, and digitigrade/palmigrade quadrupedal primates> 2012

This study analyzed humeral cortical bone thickness (Cbt) and shoulder muscle PCSA in primates with different locomotion. Gibbons, specialized brachiators, have high Cbt and small PCSA, suggesting strong passive tendon tension and internal fascia for brachiation. Chimpanzees, despite some suspensory behavior, show traits closer to quadrupeds but have larger deltoid and subscapularis muscles adapted for knuckle-walking. Cercopithecids have thin cortical bone and large PCSA, reflecting lower tendon stress in quadrupedal locomotion.

Kikuchi Y, Takemoto H, Kuraoka A.  

Journal of Anatomy, 220: 29-41. 

https://doi.org/10.1111/j.1469-7580.2011.01451.x 

<Geometric characters of the radius and tibia in Macaca mulatta and Macaca fascicularis> 2009

Comparing distal radius and tibia cross-sections in Macaca mulatta (terrestrial) and M. fascicularis (arboreal) revealed species- and sex-specific differences. M. fascicularis males showed greater bone geometry measures in fore- and hindlimbs than females, likely linked to muscle mass and leaping ability. M. mulatta had longer bones and larger tibial parameters, reflecting adaptations for flat-ground locomotion, while M. fascicularis forelimbs endure compressive stress during arboreal movement.

Kikuchi Y, Hamada Y.

Primates, 50: 169-183. 

https://doi.org/10.1007/s10329-008-0120-3 

<Quantitative analyses of cross-sectional shape of the distal radius in three species of macaques>

  2004

This study quantitatively analyzed distal radial shaft shapes in three macaque species with different locomotion. Semi-terrestrial M. fuscata showed intermediate traits between arboreal M. fascicularis and terrestrial M. mulatta. Differences in muscle groove sizes and ulnar notch shape reflect adaptations to their positional behaviors. The distal forearm morphology closely relates to muscle development and joint forces, making it useful for reconstructing locomotor habits in fossil primates.

Kikuchi Y.

Primates, 45: 129-134. 

https://doi.org/10.1007/s10329-003-0068-2 

<Morphology of brachial plexus and axillary artery in bonobo (Pan paniscus)> 2011

The first detailed study of the bonobo (Pan paniscus) brachial plexus and axillary artery shows a brachial plexus pattern similar to other apes and humans. However, the axillary artery path is unusual—it runs entirely anterior to the brachial plexus without penetrating it, a rare pattern seen in only 4.9% of humans. Additionally, the brachial artery passes superficially in front of the plexus branches.

Kikuchi Y, Oishi M, Shimizu D.

Anatomia Histologia Embryologia, 40: 68-72. 

https://doi.org/10.1111/j.1439-0264.2010.01040.x 

<Age-change of bone mineral density in the distal radius of chimpanzees and Japanese macaques>

  2003

Using pQCT, this study examined age-related changes in distal radius bone density in chimpanzees and Japanese macaques. Both species showed similar three-stage patterns, with differences in bone mineral content and timing reflecting size and lifespan variations. Their cortical bone density changes closely resemble humans, suggesting a shared bone metabolism pattern across catarrhines throughout life.

Anthropological Science, 111: 165-186. 

https://doi.org/10.1537/ase.111.165 

<Bone mineral density in chimpanzees, humans, and Japanese macaques> 2003

This study compared distal radius bone properties in chimpanzees, humans, and Japanese macaques. Chimpanzees and macaques had similar cortical bone areas, while humans had significantly less. Cortical and trabecular bone densities were consistent across species. Findings suggest chimpanzee bone properties align more with digitigrade macaques than humans, and that conserved bone metabolism maintains a necessary trabecular bone proportion for healthy turnover in catarrhines.

Kikuchi Y, Udono T, Hamada Y. 

Primates, 44: 151-155, 2003. 

https://doi.org/10.1007/s10329-002-0031-7