Effects of substrate and phylogeny on quadrupedal gait in free‐ranging platyrrhines.
arboreal quadrupedalism; MAMMALS; locomotion; platyrrhine; PHYLOGENY; QUADRUPEDALISM; NEW World monkeys; phylogenetic eigenvector; COSTA Rica
Objectives: Primate diagonal sequence (DS) gaits are often argued to be an adaptation for moving and foraging in the fine‐branch niche; however, existing data have come predominantly from laboratory studies that are limited in taxonomic breadth and fail to account for the structural and ecological variation of natural substrates. We test the extent to which substrate diameter and orientation influence gait sequence type and limb phase in free‐ranging primates, as well as how phylogenetic relatedness might condition response patterns. Materials and methods: We filmed quadrupedal locomotion in 11 platyrrhine species at field sites in Ecuador and Costa Rica and measured the diameter and orientation of locomotor substrates using remote sensors. We quantified limb phase values and classified strides by gait sequence type (N = 988 strides). Results: Our results show that most of the species in our sample consistently used DS gaits, regardless of substrate diameter or orientation; however, all taxa also used asymmetrical and/or lateral sequence gaits. By incorporating phylogenetic eigenvectors into our models, we found significant differences in gait sequence patterns and limb phase values among the major platyrrhine clades, suggesting that phylogeny may be a better predictor of gait than substrate diameter or orientation. Discussion: Our field data generally corroborate locomotor patterns from laboratory studies but capture additional aspects of gait variability and flexibility in response to the complexity of natural environments. Overall, our results suggest that DS gaits are not exclusively tailored to narrow or oblique substrates but are used on arboreal substrates in general. [ABSTRACT FROM AUTHOR]
Dunham Noah T; McNamara Allison; Shapiro Liza J; Hieronymus Tobin L; Phelps Taylor; Young Jesse W
American Journal Of Physical Anthropology
2019
2019-12
Journal Article
<a href="http://doi.org/10.1002/ajpa.23942" target="_blank" rel="noreferrer noopener">10.1002/ajpa.23942</a>
Jaw-muscle force and excursion scale with negative allometry in platyrrhine primates.
feeding behavior; fiber length; jaw-adductor muscles; New World monkeys; PCSA
OBJECTIVES: Platyrrhines span two orders of magnitude in body size and are characterized by diverse feeding behaviors and diets. While size plays an important role in primate feeding behavior and masticatory apparatus morphology, we know little about size-correlated changes in the force-generating (physiologic cross-sectional area; PCSA) and excursion/stretch (fiber length; Lf ) capabilities of the jaw-closing muscles in platyrrhines. METHODS: We examined scaling relationships of the superficial masseter and temporalis muscles in 21 platyrrhine species. Previous work suggests that larger platyrrhines are at a mechanical disadvantage for generating bite forces compared with smaller platyrrhines. We hypothesize that scaling of jaw-muscle fiber architecture counters this size-correlated decrease in mechanical advantage. Thus, we predicted that jaw-muscle PCSAs and muscle weights scale with positive allometry while Lf s scale with negative allometry, relative to load-arm estimates for incisor/molar biting and chewing. RESULTS: Jaw-muscle PCSAs and Lf s appear to scale with negative allometry relative to load-arm estimates and body size. Negative allometry of jaw-muscle weights partially accounts for the size-correlated decreases in PCSA and Lf . Estimates of bite force also scale with negative allometry. CONCLUSION: Large-bodied platyrrhines (e.g., Alouatta) are at a relative disadvantage for generating jaw-muscle and bite force as well as jaw-muscle stretch, compared with smaller species (e.g., Callithrix). The net effect is that larger platyrrhines likely produce relatively smaller maximal bite forces compared with smaller taxa. Relative to small- and intermediate-sized platyrrhines, large-bodied platyrrhines feed on some of the least mechanically challenging foods, consistent with the size-correlated decrease in relative muscle and bite forces across the clade. Am J Phys Anthropol, 2015. (c) 2015 Wiley Periodicals, Inc. Am J Phys Anthropol 158:242-256, 2015. (c) 2015 Wiley Periodicals, Inc.
Taylor Andrea B; Yuan Tian; Ross Callum F; Vinyard Christopher J
American journal of physical anthropology
2015
2015-10
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1002/ajpa.22782" target="_blank" rel="noreferrer noopener">10.1002/ajpa.22782</a>