Catarrhine hallucal metatarsals from the early Miocene site of Songhor, Kenya.

Songhor is an early Miocene fossil locality in Kenya known for its diverse primate assemblage that includes catarrhine species belonging to the genera Kalepithecus, Limnopithecus, Dendropithecus, Rangwapithecus, and Proconsul. Expeditions to Songhor since the 1930s have recovered unassociated catarrhine postcranial remains from both the fore- and hindlimbs, including multiple elements from the feet. In this study, we describe KNM-SO 31233, a complete left hallucal metatarsal (Mt1), along with several other fragmentary Mt1 specimens (KNM-SO 1080, 5129, 5141, 22235). These fossils were compared to extant catarrhines and platyrrhines, as well as available fossil Miocene catarrhine Mt1s. Morphometric data were obtained from 3D surface renderings and subjected to a number of analyses to assess their phenetic affinity with the comparative sample, make predictions of body mass, and to infer their functional morphology. The size and shape of the Songhor Mt1s are diverse, exhibiting a large robust morph (KNM-SO 5141) similar in size but not in shape to extant African apes, medium-sized morphs (KNM-SO 1080, 5129 and 22235), and a smaller, slender one (KNM-SO 31233) that has a shape resembling arboreal quadrupedal leaping monkeys and suspensory atelines and hylobatids. KNM-SO 31233 is unlike other known fossil Mt1s, and in general, none of the Songhor Mt1s resembled any single extant anthropoid clade or species. The morpho-functional diversity of Songhor Mt1s is consistent with an extensive morphological and phylogenetic catarrhine diversity in the early part of the Miocene epoch.

Sacral vertebral remains of the Middle Miocene hominoid Nacholapithecus kerioi from northern Kenya.

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 specimen, KNM-BG 42753I, is smaller than that in Old World monkeys but similar to that in extant great apes and New World monkeys, as well as Proconsul nyanzae. The relatively narrow dimensions of the first sacral vertebral body in the transverse and sagittal planes are characteristics of N. kerioi and P. nyanzae and similar to those of extant great apes. In N. kerioi, lumbosacral surface area relative to body mass is small. This may simply be an extension of a trend from the previously reported small thoracolumbar vertebrae to the sacrum. ​The first sacral vertebrae of N. kerioi and Epipliopithecus vindobonensis have a higher craniocaudal vertebral body reduction (CVR; a higher CVR indicates a wider cranial width relative to a narrower caudal width), similar to that in Old World monkeys. Old World monkeys have a higher CVR, and usually have three sacral vertebrae, fewer than seen in extant great apes, which have a lower CVR and four to six (sometimes as many as eight) sacral vertebrae. New World monkeys have a lower CVR than Old World monkeys, but generally possess only three sacral vertebrae, and have a large caudal articular surface, which may be related, at least in the Atelidae, to the grasping ability of their tails. The possibility that N. kerioi had only three sacral vertebrae cannot be ruled out, because E. vindobonensis and Old World monkeys, with higher CVRs, have sacra consisting of three sacral vertebrae.

Carpal bones of Nacholapithecus kerioi, a Middle Miocene Hominoid From Northern Kenya.

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 describe a pisiform recently assigned to the type specimen of N. kerioi, KNM-BG 35250. RESULTS: In the Nacholapithecus wrist, the ulnar styloid process articulates with both the triquetrum and pisiform, and the triquetrum facet on the hamate is relatively proximodistally oriented in dorsal view. The Nacholapithecus capitate possesses a moderate distopalmar hook-like process and separated radial articular facets for the trapezoid and the second metacarpal due to the carpometacarpal ligament attachment that is absent in the Proconsul capitate. DISCUSSION: The carpal anatomy of Nacholapithecus is similar to that of the early Miocene hominoid Proconsul. However, Nacholapithecus wrist anatomy appears to exhibit slightly more emphasized stability. Am J Phys Anthropol 160:469-482, 2016. © 2016 Wiley Periodicals, Inc.

Dental microwear profilometry of African non-cercopithecoid catarrhines of the Early Miocene.

The Early Miocene of Kenya has yielded the remains of many important stem catarrhine species that provide a glimpse of the East African primate radiation at a time of major faunal turnover. These taxa have been subject to innumerable studies, yet there is still no consensus on their dietary niches. Here we report results of an analysis of dental microwear textures of non-cercopithecoid catarrhines from the Early Miocene of Kenya. Scanning confocal profilometry of all available molar specimens with undamaged occlusal surfaces revealed 82 individuals with unobscured antemortem microwear, representing Dendropithecus, Micropithecus, Limnopithecus, Proconsul, and Rangwapithecus. Scale-sensitive fractal analysis was used to generate microwear texture attributes for each individual, and the fossil taxa were compared with each other using conservative non-parametric statistical tests. This study revealed no discernible variation in microwear texture among the fossil taxa, which is consistent with results from a previous feature-based microwear study using smaller samples. Our results suggest that, despite their morphological differences, these taxa likely often consumed foods with similar abrasive and fracture properties. However, statistical analyses of microwear texture data indicate differences between the Miocene fossil sample and several extant anthropoid primate genera. This suggests that the African non-cercopithecoid catarrhines included in our study, despite variations in tooth form, had generalist diets that were not yet specialized to the degree of many modern taxa.

First steps of bipedality in hominids: evidence from the atelid and proconsulid pelvis.

Upright walking absent a bent-hip-bent-knee gait requires lumbar lordosis, a ubiquitous feature in all hominids for which it can be observed. Its first appearance is therefore a central problem in human evolution. Atelids, which use the tail during suspension, exhibit demonstrable lordosis and can achieve full extension of their hind limbs during terrestrial upright stance. Although obviously homoplastic with hominids, the pelvic mechanisms facilitating lordosis appear largely similar in both taxa with respect to abbreviation of upper iliac height coupled with broad sacral alae. Both provide spatial separation of the most caudal lumbar(s) from the iliac blades. A broad sacrum is therefore a likely facet of earliest hominid bipedality. All tailed monkeys have broad alae. By contrast all extant apes have very narrow sacra, which promote "trapping" of their most caudal lumbars to achieve lower trunk rigidity during suspension. The alae in the tailless proconsul Ekembo nyanzae appear to have been quite broad, a character state that may have been primitive in Miocene hominoids not yet adapted to suspension and, by extension, exaptive for earliest bipedality in the hominid/panid last common ancestor. This hypothesis receives strong support from other anatomical systems preserved in Ardipithecus ramidus.