Odd-nosed Monkey Scapular Morphology Is Convergent with Hominoids and Atelines

Reconstruction of hominoid locomotor evolution necessarily relies on analogies with extant taxa. Recent studies have shown that odd-nosed monkeys utilize more varied locomotor modes than other cercopithecoids, including below branch locomotion, and converge behaviorally with hominoids and atelines. Odd-nosed monkeys are more closely related to hominoids than atelines and also lack a prehensile tail, making them potential models for early hominoid locomotor behavior. Here, we test if locomotor behaviors of odd-nosed monkeys are reflected in their scapulae. Specifically, we test several ratios and angles that identify suspensory and clambering features, to see if odd-nosed monkeys ( Nasalis , Pygathrix , and Rhinopithecus ) are more similar to apes than other cercopithecoids. Principal components analysis separates taxa based on mediolateral breadth, and spine and glenoid orientation, with hominoids having positive loadings and cercopithecines negative. Atelines and odd-nosed monkeys are closer to hominoids, with cebines and other colobines intermediate. When each angle and ratio is considered individually, odd-nosed monkeys and Piliocolobus are consistently the closest taxa among cercopithecoids to, and often having overlapping values with, atelines and hominoids. Odd-nosed monkeys have glenoid angles comparable to Alouatta and Lagothrix , spine angles similar to Pongo and Gorilla , and mediolateral breadth ratios intermediate between hominoids and other colobines. These results show that odd-nosed monkeys are the most similar among cercopithecoids to hominoid scapular morphology. They are convergent with, but less highly derived than Ateles , Pan and hylobatids. Furthermore, such convergence supports previous functional interpretations of hominoid scapular morphology as adaptations for suspensory and/or clambering locomotion.