New femoral remains of Nacholapithecus kerioi: Implications for intraspecific variation and Miocene hominoid evolution

Marta Pina; Yasuhiro Kikuchi; Masato Nakatsukasa; Yoshihiko Nakano; Yutaka Kunimatsu; Naomichi Ogihara; Daisuke Shimizu; Tomo Takano; Hiroshi Tsujikawa; Hidemi Ishida

doi:10.1016/j.jhevol.2021.102982

New femoral remains of Nacholapithecus kerioi: Implications for intraspecific variation and Miocene hominoid evolution

J Hum Evol. 2021 Jun:155:102982. doi: 10.1016/j.jhevol.2021.102982. Epub 2021 Apr 13.

Authors

Affiliations

¹ Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan; Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, C/ Columnes S/n, Campus de La UAB, 08193, Cerdanyola Del Vallès, Barcelona, Spain. Electronic address: marta.pinamiguel@manchester.ac.uk.
² Division of Human Anatomy and Biological Anthropology, Department of Anatomy and Physiology, Faculty of Medicine, Saga University, Saga, 849-8501, Japan.
³ Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan.
⁴ Department of Biological Anthropology, Osaka University, Suita, Osaka, 565-8502, Japan.
⁵ Department of Business Administration, Faculty of Business Administration, Ryukoku University, Kyoto, 612-8577, Japan.
⁶ Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, 113-0033, Japan.
⁷ Faculty of Nursing and Rehabilitation, Chubu Gakuin University, Seki, Gifu, 504-0837, Japan.
⁸ Japan Monkey Centre, Aichi, 484-0081, Japan.
⁹ Department of Rehabilitation, Faculty of Medical Science and Welfare, Tohoku Bunka Gakuen University, Sendai, 981-8551, Japan.
¹⁰ Kyoto University, Kyoto, 606-8502, Japan.

PMID: 33862402
DOI: 10.1016/j.jhevol.2021.102982

Abstract

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).

Keywords: Femur; Functional morphology; Miocene hominoids; Positional behavior.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Biological Evolution*
Female
Femur / anatomy & histology*
Fossils*
Hominidae / anatomy & histology*
Hominidae / classification*
Hominidae / physiology
Kenya
Male
Species Specificity