The Hand of Cercopithecoides williamsi (Mammalia, Primates): Earliest Evidence for Thumb Reduction among Colobine Monkeys.

Thumb reduction is among the most important features distinguishing the African and Asian colobines from each other and from other Old World monkeys. In this study we demonstrate that the partial skeleton KNM-ER 4420 from Koobi Fora, Kenya, dated to 1.9 Ma and assigned to the Plio-Pleistocene colobine species Cercopithecoides williamsi, shows marked reduction of its first metacarpal relative to the medial metacarpals. Thus, KNM-ER 4420 is the first documented occurrence of cercopithecid pollical reduction in the fossil record. In the size of its first metacarpal relative to the medial metacarpals, C. williamsi is similar to extant African colobines, but different from cercopithecines, extant Asian colobines and the Late Miocene colobines Microcolobus and Mesopithecus. This feature clearly links the genus Cercopithecoides with the extant African colobine clade and makes it the first definitive African colobine in the fossil record. The postcranial adaptations to terrestriality in Cercopithecoides are most likely secondary, while ancestral colobinans (and colobines) were arboreal. Finally, the absence of any evidence for pollical reduction in Mesopithecus implies either independent thumb reduction in African and Asian colobines or multiple colobine dispersal events out of Africa. Based on the available evidence, we consider the first scenario more likely.

Pattern and pace of dental eruption in Tarsius.

This article uses data on the dental eruption pattern and life history of Tarsius to test the utility of Schultz's rule. Schultz's rule claims a relationship between the relative pattern of eruption and the absolute pace of dental development and life history and may be useful in reconstructing life histories in extinct primates. Here, we document an unusual eruption pattern in Tarsius combining early eruption (relative to molars) of anterior replacement teeth (P2 and incisors) and relatively late eruption of the posterior replacement teeth (C, P3, and P4). This eruption pattern does not accurately predict the "slow" pace of life documented for Tarsius [Roberts: Int J Primatol 15 (1994) 1-28], nor aspects of life history directly associated with dental development as would be expected using Schultz's rule. In Tarsius, the anterior teeth and M1 erupt at an early age and therefore are not only fast in a relative sense but also fast in an absolute sense. This seems to be related to a developmental anomaly in the deciduous precursor teeth, which are essentially skipped. This decoupling among dental eruption pattern, dental eruption pace, and life history pace in Tarsius undermines the assumptions that life histories can accurately be described as "fast" or "slow" and that dental eruption pattern alone can be used to infer overall life history pace. The relatively and absolutely early eruption of the anterior dentition may be due to the utility of these front teeth in early food acquisition rather than with the pace of life history.

Geometric morphometric analysis of tibial shape and presentation among Catarrhine taxa.

The proximal component of the talo-crural joint, the tibia, was compared, using geometric morphometrics, in 240 specimens from 10 extant taxa to identify differences in shape and the factors influencing them. The specimens were laser scanned, digitally reconstructed, and landmarked. Regression analysis was used to evaluate tibial shape, and significant amounts of shape variation among taxa were due to body mass, tibial size, superfamily, and substrate preference in the whole tibia, as well as, separate analysis of the distal tibial articular facets, and the medial malleolar facet. The most important factor for whole tibial shape was tibial robusticity, which closely correlated with body mass. However, substrate preference was also a significant factor in tibial shape and independent from body mass. Substrate preference was also the most important factor defining distal articular morphology. Principal components analysis and pairwise permutation tests were used to compare differences in morphology among taxa. Nearly all were significantly different in overall tibial shape, and distal morphology. Shape and presentational morphology associated with body mass, tibial size, superfamily, and substrate preference were identified, along with the similarities and differences among individual taxa. These were visualized by TPS deformation of an exemplar surface. Relationships among these factors were assessed with their dot-product. Results demonstrated that size significantly influenced proximal presentation, while substrate preference influenced articular morphology.

Bringing up baby: Developmental simulation of the adult cranial morphology of rungwecebus kipunji.

Rungwecebus kipunji is a recently discovered, critically endangered primate endemic to southern Tanzania. Although phenetically similar to mangabeys, molecular analyses suggest it is more closely related to Papio or possibly descended from an ancient population of baboon-mangabey hybrids. At present, only a single kipunji specimen, an M1-stage juvenile male, is available for study; thus, the cranial morphology of the adult kipunji is unknown. In this study, we used developmental simulation to estimate the adult kipunji's 3D cranial morphology. We examined variation in cercopithecine developmental vectors, applied selected vectors to the juvenile cranium, and compared the resulting simulated adults to actual adult male papionins. Differences between papionin developmental vectors were small and statistically insignificant. This uniformity suggests conservation of an ancestral papionin developmental program. Simulated kipunji adults were likewise extremely similar. As a group, the simulated adults were morphometrically distinct from other papionins, corroborating the kipunji's generic status. Simulated adults were phenetically most similar to Lophocebus aterrimus but were distinguished from all adult papionins by the same unique traits that characterize the kipunji juvenile: a tall neurocranium, broad face, short nasal bones, concave anteorbital profile, and dorsally rotated palate. This concordance between juvenile and estimated-adult morphologies confirms that papionin cranial shape is largely established before M1 eruption. The estimated kipunji adult's neurocranium strongly resembles that of Papio, providing the first cranial evidence supporting their phylogenetic relationship. If the kipunji does indeed have a hybrid origin, then its phenetic affinity to L. aterrimus favors Lophocebus as the proto-kipunji's paternal lineage.