Assessing thoraco‐pelvic covariation in Homo sapiens and Pan troglodytes: A 3D geometric morphometric approach

Abstract

Objectives: Understanding thoraco-pelvic integration in Homo sapiens and their closest living relatives (genus Pan) is of great importance within the context of human body shape evolution. However, studies assessing thoraco-pelvic covariation across Hominoidea species are scarce, although recent research would suggest shared covariation patterns in humans and chimpanzees but also species-specific features, with sexual dimorphism and allometry influencing thoraco-pelvic covariation in these taxa differently. Material and Methods: N = 30 adult H. sapiens and N = 10 adult Pan troglodytes torso 3D models were analyzed using 3D geometric morphometrics and linear measurements. Effects of sexual dimorphism and allometry on thoraco-pelvic covariation were assessed via regression analyses, and patterns of thoraco-pelvic covariation in humans and chimpanzees were computed via Two-Block Partial Least Squares analyses. Results: Results confirm the existence of common aspects of thoraco-pelvic covariation in humans and chimpanzees, and also species-specific covariation in H. sapiens that is strongly influenced by sexual dimorphism and allometry. Species-specific covariation patterns in chimpanzees could not be confirmed because of the small sample size, but metrics point to a correspondence between the most caudal ribs and iliac crest morphology that would be irrespective of sex. Conclusions: This study suggests that humans and chimpanzees share common aspects of thoraco-pelvic covariation but might differ in others. In humans, torso integration is strongly influenced by sexual dimorphism and allometry, whilst in chimpanzees it may not be. This study also highlights the importance not only of torso widths but also of torso depths when describing patterns of thoraco-pelvic covariation in primates. Larger samples are necessary to support these interpretations.

An integrative approach to examining the influences of size, phylogeny, and locomotion on os coxae shape variation in primates

“…However, African apes exhibit multiple musculoskeletal adaptations to suspension including features of the shoulder girdle and torso (Almécija et al, 2021; Larson, 1998; Nakatsukasa, 2019; Thompson et al, 2018; Ward, 2015). Given recent work examining covariation between torso morphology and pelvis morphology (Torres‐Tamayo et al, 2020), we might expect the pelvis of African apes to be at least as influenced by suspension as it is by terrestrial locomotion. Indeed, if all nonhuman apes examined here were categorized as suspensory, they would occupy a region of the phylomorphospace with suspensory atelines and would not overlap any other locomotor groups (Figures 2 and 3).…”

“…The majority of previous work on functional correlates of pelvic morphology in primates has examined linear measures (e.g., ilium length, ilium width, ischium length) in both univariate and multivariate analyses and related these linear measures to locomotion (e.g., Anemone, 1993; Ashton et al, 1981; Berge, 1984; Fleagle & Anapol, 1992; Hammond & Almécija, 2017; Leutenegger, 1974; Lewton, 2015a, 2015b; Lewton & Scott, 2017; Morgan et al, 2015; Steudel, 1981; Ward, 1991, 1993; Waterman, 1929). Compared to other aspects of the postcranial skeleton, there have been relatively few studies on 3D pelvic shape (but see Betti et al, 2014; Fatica et al, 2019; Fischer & Mitteroecker, 2015; Lewton, 2015a, 2015b; Lycett & von Cramon‐Taubadel, 2013; Middleton et al, 2017; Moffett, 2017, 2021; Torres‐Tamayo et al, 2020; Ward et al, 2018) and these have either focused on specific clades (e.g., strepsirrhines [Lewton, 2015b]; anthropoids [Moffett, 2017; Ward et al, 2018]; catarrhines [Lycett & von Cramon‐Taubadel, 2013]; gorillas [Fatica et al, 2019]; humans [Betti et al, 2014]) or did not incorporate phylogenetic comparative methods. As a result, our understanding of how function, phylogeny, and body size together affect 3D primate pelvic shape remains limited.…”

New insights into patterns of integration in the femur and pelvis among catarrhines

“…Moreover, some authors have shown that in humans, pelvic morphology displays integration with other anatomical areas. Examples include elements of the shoulder girdle and rib cage (Agosto & Auerbach, 2022; Torres‐Tamayo, Martelli, et al, 2020; Torres‐Tamayo, Schlager, et al, 2020), and even proposed covariation with skull size in relation to obstetrical selection pressure (Fischer & Mitteroecker, 2015). Comparable morphological integrations are not documented in chimpanzees and baboons.…”

“…This approach has been broadly used in biological anthropology to describe and quantify morphology of several anatomical features (for a review see Mitteroecker & Schaefer, 2022). Furthermore, the use of geometric morphometric datasets is common in the study of integration (Agosto & Auerbach, 2022; Hanot et al, 2018; Klingenberg, 2009; Komza et al, 2022; Neaux et al, 2017; Torres‐Tamayo, Martelli, et al, 2020; Torres‐Tamayo, Schlager, et al, 2020).…”

Sex classification using the human sacrum: Geometric morphometrics versus conventional approaches

“…Moreover, interactions between the independent variables were investigated using Procrustes ANOVAs with the ‘advanced.procD.lm’ function in the R geomorph package [ 50 , 51 ]. To further account for potential sex driven allometric trends within the sample, the protocol of Torres-Tamayo et al [ 52 ] and their corresponding R script (available from https://osf.io/zrgbf/?view_only=ffd87b50e6744ca780d43a758403d05a ) was implemented to isolate size effects. The latter analysis was performed by regressing the allometric residuals (dependent variable) on sex (independent variable) in binary form.…”