Relationships between the hard and soft dimensions of the nose in Pan troglodytes and Homo sapiens reveal the positions of the nasal tips of Plio-Pleistocene hominids.

By identifying homogeneity in bone and soft tissue covariation patterns in living hominids, it is possible to produce facial approximation methods with interspecies compatibility. These methods may be useful for producing facial approximations of fossil hominids that are more realistic than currently possible. In this study, we conducted an interspecific comparison of the nasomaxillary region in chimpanzees and modern humans with the aim of producing a method for predicting the positions of the nasal tips of Plio-Pleistocene hominids. We addressed this aim by first collecting and performing regression analyses of linear and angular measurements of nasal cavity length and inclination in modern humans (Homo sapiens; n = 72) and chimpanzees (Pan troglodytes; n = 19), and then performing a set of out-of-group tests. The first test was performed on four subjects that belonged to the same genus as the training sample, i.e., Homo (n = 2) and Pan (n = 2), and the second test, which functioned as an interspecies compatibility test, was performed on Pan paniscus (n = 1), Gorilla gorilla (n = 3), Pongo pygmaeus (n = 1), Pongo abelli (n = 1), Symphalangus syndactylus (n = 3), and Papio hamadryas (n = 3). We identified statistically significant correlations in both humans and chimpanzees with slopes that displayed homogeneity of covariation. Prediction formulae combining these data were found to be compatible with humans and chimpanzees as well as all other African great apes, i.e., bonobos and gorillas. The main conclusion that can be drawn from this study is that our set of regression models for approximating the position of the nasal tip are homogenous among humans and African apes, and can thus be reasonably extended to ancestors leading to these clades.

Towards the restoration of ancient hominid craniofacial anatomy: Chimpanzee morphology reveals covariation between craniometrics and facial soft tissue thickness.

In modern humans, facial soft tissue thicknesses have been shown to covary with craniometric dimensions. However, to date it has not been confirmed whether these relationships are shared with non-human apes. In this study, we analyze these relationships in chimpanzees (Pan troglodytes) with the aim of producing regression models for approximating facial soft tissue thicknesses in Plio-Pleistocene hominids. Using CT scans of 19 subjects, 637 soft tissue, and 349 craniometric measurements, statistically significant multiple regression models were established for 26 points on the face and head. Examination of regression model validity resulted in minimal differences between observed and predicted soft tissue thickness values. Assessment of interspecies compatibility using a bonobo (Pan paniscus) and modern human subject resulted in minimal differences for the bonobo but large differences for the modern human. These results clearly show that (1) soft tissue thicknesses covary with craniometric dimensions in P. troglodytes, (2) confirms that such covariation is uniformly present in both extant Homo and Pan species, and (3) suggests that chimp-derived regression models have interspecies compatibility with hominids who have similar craniometric dimensions to P. troglodytes. As the craniometric dimensions of early hominids, such as South African australopithecines, are more similar to P. troglodytes than those of H. sapiens, chimpanzee-derived regression models may be used for approximating their craniofacial anatomy. It is hoped that the results of the present study and the reference dataset for facial soft tissue thicknesses of chimpanzees it provides will encourage further research into this topic.

Variation in obstetric dimensions of the human bony pelvis in relation to age-at-death and latitude.

OBJECTIVES: Previous studies associate females who died in young adulthood with narrower obstetric pelvic dimensions, presumably in association with obstetric insufficiency (though this causal relationship is unresolved). In this study, we examine whether females within groups living at higher latitudes present this pattern, as high-latitude groups have larger pelvic dimensions than groups previously examined. These patterns are compared with males. We assess whether there is evidence for younger ages-at-death in females to have been in response to natural selection against narrower true pelvis dimensions. METHODS: We measured 14 pelvic dimensions in 327 adults (188 females, 139 males), representing archaeological sites from mid-latitude and high-latitude North America. Individuals were placed into a "young" or "not young" age-at-death category. Latitude, sex, and age-at-death groups were compared using ANOVAs and scaled variance, and evidence for selection was examined with F-tests. RESULTS: Pelvic dimensions were larger in high-latitude females and males. Females but not males who died at younger ages had smaller pelvic canals than older individuals, especially in the mediolateral inlet and anteroposterior outlet dimensions. Variance in all pelvic dimensions is equal between the two female age-at-death groups. CONCLUSIONS: We found narrower obstetrical dimensions in the female pelvis among individuals who died at younger ages. However, statistically equivalent variances in the two female age-at-death groups does not support natural selection on pelvic dimensions as leading to younger ages at death. We instead argue that this difference is result of continued growth due to remodeling in the pelvis occurring in females, but not males, after early adulthood.

Dietary signals in the premolar dentition of primates.

Dietary adaptations specific to the premolar row remain largely undocumented across primates. This study examines how relative premolar size varies among broad dietary groups (i.e., folivores, frugivores, insectivores, hard-object feeders) using a phylogenetically and ecologically diverse sample of species. We quantified relative premolar size with shape ratios computed using mandibular length, body mass, palate area, and M1 area to evaluate hypotheses that link variation in relative premolar size to differences in tooth loading, energy requirements, the probability of tooth-food-tooth contact during mastication, and shifts in preferred bite point. Our results revealed the following dietary signals. First, primate folivores have large premolar rows relative to palate area in comparison to frugivores and insectivores. This contrast is consistent with the hypothesis that folivores require large postcanine teeth relative to the size of the oral cavity to increase the probability of particle fracture during mastication. Second, hard-object feeders are distinct from other groups in having P4s that are large relative to their M1s. This morphology is not associated with an increase in the size of the premolar row relative to mandibular length. This combination challenges the idea that hard-object feeders have large premolars as an adaptive response to resisting the loads incurred when processing mechanically challenging foods. We therefore interpret the large P4/M1 ratios of hard-object feeders as indicating greater functional integration across the premolar-molar boundary owing to a mesial shift in preferred bite point. Finally, in a restricted subset of anthropoids, we found that, relative to mandibular length, premolar area increases with dietary elastic modulus (E) and toughness (R), indicating that relative premolar size is evolutionarily sensitive to food mechanical properties. Thus, our results show that relative premolar size is correlated with diet, highlighting the importance of this region for understanding the evolutionary history of primate dietary adaptations.