Is the Locomotor Diversity in Odd-Nosed Monkeys Reflected in Their Olecranon Size or Orientation?

More suspensory anthropoids typically have relatively short and posteriorly oriented olecranon processes. Odd-nosed monkeys perform more suspensory locomotor behavior than other colobines and have been shown to have a lower olecranon to ulna ratio, however, their olecranon lengths relative to body size and olecranon orientations have not been described. Here, odd-nosed monkeys are compared to a broad sample of anthropoids to see if their olecranon length and orientation resemble apes or spider monkeys more so than other colobines. Olecranon and distal ulna lengths were measured from the center of rotation at the trochlear notch, with olecranon orientation defined as the angle between these two lines. Size was corrected by a geometric mean of limb joint surfaces. Angles and ratios were compared by ANOVA with Bonferroni post hoc adjustment. Olecranon/ distal ulna length ratio is lowest in highly suspensory anthropoids: hylobatids, Pongo, and Ateles. Odd-nosed monkeys and Presbytis have the next lowest ratios. Relative olecranon length is shortest among hominoids; odd-nosed monkeys, Ateles, Presbytis and Piliocolobus have the next lowest ratios. Hylobatids have the longest distal ulnae, while Pygathrix, Ateles, Presbytis, and Erythrocebus have the next longest, followed by Pongo, Nasalis, Mandrillus, and Theropithecus. Hominoids have the most posteriorly oriented olecranons, but olecranon angle does not significantly differ between odd-nosed monkeys and other arboreal cercopithecines. Odd-nosed monkeys, therefore, are intermediate to hominoids and other colobines in olecranon length, but not orientation. Whether this reflects current differences in locomotor behaviors or nascent suspensory adaptations requires further investigation.