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

Ryan M Campbell,Gabriel Vinas,Maciej Henneberg,Caroline Wilkinson

doi:10.1371/journal.pone.0245760

Ryan M Campbell, Gabriel Vinas + Show 2 more

Open Access

https://doi.org/10.1371/journal.pone.0245760

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Abstract

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.

Highlights

The primate family of Hominidae is comprised of the African apes, humans and all ancestors leading to these clades
The present study is motivated by the aforementioned concerns and while we hold that the findings reported here are valuable we raise three caveats at the outset: 1) As in previous studies of chimpanzee soft tissues [24,25,26], this study includes only a small sample of chimpanzees and, the conclusions from the results are subject to further testing on larger samples; 2) We do not include other members of the African ape clade and so we cannot expand our findings to the entire Hominoidea superfamily; and 3) We do not claim to eliminate the need for informed speculation in hominid facial approximation entirely
The results of this study show that soft tissue and craniometric measurements covary in chimpanzees, which confirms that such covariation is uniformly present in both extant Homo and Pan species

Summary

Introduction

The primate family of Hominidae is comprised of the African apes, humans and all ancestors leading to these clades. Hominidae, called here hominids, has become an increasingly popular practice with many approximations of their faces presented in museum exhibitions, popular science publications, and at conference presentations worldwide [1,2,3]. In these contexts, reconstructions of the face and body have proven to be an effective vehicle for the dissemination of scientific information about human evolution. There is clearly variation in the replicability across existing reconstruction methods depending on the robustness of the empirical data supporting them and, since there is currently very little applicable data that can be extrapolated to Plio/Pleistocene hominids, results vary depending on methods used and individualities of practitioners

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