Vertebral morphology of Nacholapithecus kerioi based on KNM-BG 35250 Masato Nakatsukasa a, * , Yutaka Kunimatsu b , Yoshihiko Nakano c , Hidemi Ishida d a Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Kyoto 6068502, Japan b Primate Research Institute, Kyoto University, Aichi 4848506, Japan c Department of Biological Anthropology, Osaka University, Osaka 5650871, Japan d Department of Human Nursing, University of Shiga Prefecture, Hikone, Shiga 5228533, Japan Received 2 May 2005; accepted 8 August 2006 Abstract 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. Ó 2006 Published by Elsevier Ltd. Keywords: East Africa; Fossils; Locomotion; Lumbar stability; Miocene hominoid; Spine Introduction The discovery of the KNM-BG 35250 Nacholapithecus kerioi skeleton from Nachola, northern Kenya (ca. 15 Ma) pro- vides an opportunity to refine evolutionary and phylogenetic hypotheses of Miocene hominoids (Ishida et al., 2004). The present paper describes the vertebral part of this skeleton and discusses its functional adaptations. The vertebral column is a key region for analysis of primate locomotor behavior (Slijper, 1946; Erikson, 1963; Rose, 1975), as well as for assessment of hominoid phylogeny (Pilbeam, 1996, 2004). Unfortunately, vertebral specimens are less abundant than limb bone specimens in fossil hominoid postcranial collec- tions. The vertebral remains of N. kerioi expand the existing sample of fossil hominoid (and propliopithecoid) vertebral el- ements. Fossil vertebrae are also known for Proconsul nyanzae (Ward, 1993; Ward et al., 1993), P. heseloni (Walker and Pickford, 1983), Morotopithecus bishopi (Walker and Rose, 1968; Sanders and Bodenbender, 1994; MacLatchy et al., * Corresponding author. E-mail addresses: nakatsuk@anthro.zool.kyoto-u.ac.jp (M. Nakatsukasa), kunimat@pri.kyoto-u.ac.jp (Y. Kunimatsu), nakano@hus.osaka-u.ac.jp (Y. Nakano), hishida@nurse.usp.ac.jp (H. Ishida). 0047-2484/$ - see front matter Ó 2006 Published by Elsevier Ltd. doi:10.1016/j.jhevol.2006.08.008 Journal of Human Evolution 52 (2007) 347e369