Scapular breadth is associated with forelimb‐dominated suspensory behavior in Atelidae: Comments on Selby and Lovejoy (2017)

Abstract

Scapular breadth is associated with forelimb-dominated suspensory behavior in Atelidae: Comments on Selby and Lovejoy (2017) Recently, Selby and Lovejoy (2017) argued that most apparent synapomorphies in the hominoid scapula are not independent adaptive traits but rather secondary developmental characters driven by a few underlying adaptive changes. According to their argument, chief among these adaptive changes is the mediolateral narrowing of the hominoid scapula. This interpretation is consistent with recent work suggesting that scapular blade shape is the most phylogenetically conserved aspect of the hominoid scapula (Young, Capellini, Roach, & Alemseged, 2015). Selby and Lovejoy (2017) then assert, contrary to previously published work (e.g., Hunt, 1991;Green, 2013), that a mediolaterally narrow scapula is unrelated to suspensory locomotion and therefore that early crown hominoids could not have been suspensory and were instead clambering arboreal quadrupeds. This conclusion is based on their assertion that among extant border height, while both are narrower than either Lagothrix or Cebus (P < .0001). When the ratio of scapular border size relative to geometric mean is calculated, this relationship disappears. Instead, Ateles has the narrowest scapula, followed by Lagothrix, then Alouatta, and finally Cebus (Figure 1B; P < .002 for all pairwise comparisons). Based on published descriptions of atelid positional repertoires (Cant, Youlatos, and Rose, 2001;Defler, 1999;Fontaine 1990;Gebo, 1992), the taxa with the narrowest scapulae are also the most suspensory ( Figure 1B). This pattern holds whether only suspensory locomotion (P < .0001, R 2 5 .81), only suspensory positional behavior (P < .0001, R 2 5 .80), or the full positional repertoire (P < .0001, R 2 5 .82) of each genus is considered.The discrepancy between our results and those reported by Selby and Lovejoy (2017) is driven by the relatively tall vertebral border of Alouatta ( Figure 1C). Further, the relationship we observed between scapular narrowness and suspension is not explained by allometry or other factors potentially associated with suspension, such as the angle of the vertebral spine or long arms. Selby and Lovejoy (2017) found a slightly positively allometric trend in the vertebral border of anthropoids, but the smallest primate analyzed here, Cebus, has the second largest relative vertebral border height while the largest primate, Ateles, Am J Phys Anthropol. 2018;1-3. wileyonlinelibrary.com/journal/ajpa V C 2018 Wiley Periodicals, Inc. | 1

Scapular breadth does not discriminate suspension from clambering in hominoids: A response to Spear and Williams

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Spear and Williams (2018) are incorrect in stating that we (Selby & Lovejoy, 2017) argued that "a mediolaterally narrow scapula is unrelated to suspensory locomotion and therefore. .

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