Carpal allometry of African apes among mammals

Abstract

Objectives Morphological variation in African ape carpals has been used to support the idea that Pan and Gorilla evolved knuckle‐walking independently. Little work, however, has focused on the effect of body mass on carpal morphology. Here, we compare carpal allometry in Pan and Gorilla to that of other quadrupedal mammals with similar body mass differences. If allometric trends in Pan and Gorilla carpals mirror those of other mammals with similar body mass variation, then body mass differences may provide a more parsimonious explanation for African ape carpal variation than the independent evolution of knuckle‐walking. Materials and Methods Three linear measurements were collected on the capitate, hamate, lunate, and scaphoid (or scapholunate) of 39 quadrupedal species from six mammalian families/subfamilies. Relationships between linear measurements and estimated body mass were analyzed using reduced major axis regression. Slopes were compared to 0.33 for isometry. Results Within Hominidae, higher body mass taxa (Gorilla) have relatively anteroposteriorly wider, mediolaterally wider, and/or proximodistally shorter capitates, hamates, and scaphoids than low body mass taxa (Pan). These allometric relationships are mirrored in most, but not all, mammalian families/subfamilies included in the analysis. Conclusions Within most mammalian families/subfamilies, carpals of high body mass taxa are proximodistally shorter, anteroposteriorly wider, and mediolaterally wider than those of low body mass taxa. These distinctions may be caused by the need to accommodate relatively higher forelimb loading associated with greater body mass. Because these trends occur within multiple mammalian families/subfamilies, some carpal variation in Pan and Gorilla is consistent with body mass differences.

A Bayesian model‐based reduced major axis regression

“…In addition, RMA is less prone to outliers and the relationship between the two assessed variables can be described by physical laws (Carroll & Ruppert, 1996;Hatvani et al, 2023). Due to these properties, RMA is widely used in zoology, botany, ecology, forestry, biology, and spectroscopy, see Brenner et al (2023), Dai et al (2019), de Jesús Martín-Camacho et al (2023), Dufeau and Witmer (2015), Goldstein and Sylvester (2023), Huang et al (2019), Islam et al (2016), Labonte et al (2016), Mason et al (2023), and among others.…”

“…(2019), de Jesús Martín‐Camacho et al. (2023), Dufeau and Witmer (2015), Goldstein and Sylvester (2023), Huang et al. (2019), Islam et al.…”