Mandibular shape variation in mainland and insular hylobatids

Abstract

Although hylobatids are the most speciose of the living apes, their morphological interspecies and intraspecies variation remains poorly understood. Here, we assess mandibular shape variation in two species of Hylobates, white‐handed (Hylobates lar) and black‐handed (Hylobates agilis) gibbons. Using 71 three‐dimensional landmarks to quantify mandibular shape, interspecies and intraspecies variation and geographic patterns of mandibular shape are examined in a mixed sex sample of adult H. lar and H. agilis through generalized Procrustes analysis, Procrustes analysis of variance, and principal components analysis. We find that relative to H. agilis, H. lar exhibits a higher amount of variation in mandibular shape. Both species demonstrate similar allometric patterns in mandibular shape. We also highlight a geographic pattern in mandibular shape variation. Compared to mainland hylobatids, insular hylobatids have relatively lower, more posteriorly oriented, and anteroposteriorly wider mandibular condyles, with an increased distance between the condyles and the coronoid processes. This geographic pattern could reflect differences in functional demands on the mandible during mastication and/or could be driven by factors often associated with evolutionary pressures of island populations relative to mainland populations. The findings of this study highlight how little is known about Hylobates morphological variation and how important this is for using Hylobates to help interpret the primate fossil record. Understanding interspecific and intraspecific variation in extant primates is vital to interpreting variation in the primate fossil record.

Anatomy of the mandibular corpus of extant cercopithecids : taxonomy and variation

“…The shape of the extant catarrhines corpus is a useful taxonomic discriminator and has been implicated in taxonomic discrimination among extant cercopithecoids (Takahashi and Pan, 1994; Jablonski et al, 1998; Daegling and McGraw, 2001; Pan et al, 2002, 2008; Wright et al, 2008) and hominoids (Daegling, 1989; Humphrey et al, 1999; Taylor, 2002; Taylor and Groves, 2003; Taylor, 2006a; Pitirri and Begun, 2019; Pitirri et al, 2020). The sources of variation in corpus shape, notably sexual dimorphism and ontogeny, were clarified in extant hominoids (Wood et al, 1991; Daegling, 1996; Brown, 1997; Taylor, 2006b; Singh, 2014; Pitirri and Begun, 2020).…”

Comparison of captive and wild fascicularis‐group macaques (Primates, Cercopithecidae) provides insight into cranial form changes in response to rapid environmental changes

“…Across anthropoid primates, several geographically widespread clades exhibit patterns of morphological covariation with geographic and environmental parameters (e.g., Cáceres et al, 2014; Cardini et al, 2007; Cardini & Elton, 2009; Fooden & Albrecht, 1993; Frost et al, 2003; Groves, 1970; Grunstra et al, 2018; Harvati & Weaver, 2006; Jabbour & Pearman, 2016; Meloro, Cáceres, Carotenuto, Passaro, et al, 2014; Pitirri et al, 2020; Turner et al, 1997, 2018; Weinstein, 2011). In particular, latitudinal patterns in body size and relative limb lengths reflecting Bergmann's and Allen's rules respectively have been observed in many mammalian taxa, including primates (e.g., Albrecht & Miller, 1993; Ashton et al, 2000; Harcourt & Schreier, 2009; Meiri & Dayan, 2003; Turner et al, 2018; Weinstein, 2011).…”

Deciphering the mandibular shape variation in a group of Malagasy primates using Fourier outline analysis

“…Factors threatening primates are dynamic and interact with each other at local, regional, and national scales, leading to a reduction in population sizes and, a probable extinction (Estrada et al, 2017). Previous studies have shown that morphology covaries with ecological parameters in Malagasy primates (e.g., Andrews et al, 2020;Meloro et al, 2015;Pitirri et al, 2020;Pitirri & Begun, 2019;Raveloson et al, 2005;Ravosa, 1990Ravosa, , 1991Ravosa, , 1992Ross et al, 2012) but also that the morphofunctional adaptations are difficult to discern from other sources of mandibular variation (e.g., Humphrey et al, 1999;Marcé-Nogué et al, 2017;Meloro et al, 2015;Pitirri et al, 2020;Raveloson et al, 2005;Ravosa, 1990;Ross et al, 2012;Schmittbuhl et al, 2007;Taylor & Groves, 2003). In addition, morphology clearly carries a phylogenetic signal (Fleagle et al, 2010(Fleagle et al, , 2016Masters et al, 2014;Masters & Couette, 2015;St Clair & Boyer, 2016).…”