Scaling of Primate Forearm Muscle Architecture as It Relates to Locomotion and Posture

Abstract

It has been previously proposed that distal humerus morphology may reflect the locomotor pattern and substrate preferred by different primates. However, relationships between these behaviors and the morphological capabilities of muscles originating on these osteological structures have not been fully explored. Here, we present data about forearm muscle architecture in a sample of 44 primate species (N = 55 specimens): 9 strepsirrhines, 15 platyrrhines, and 20 catarrhines. The sample includes all major locomotor and substrate use groups. We isolated each antebrachial muscle and categorized them into functional groups: wrist and digital extensors and flexors, antebrachial mm. that do not cross the wrist, and functional combinations thereof. Muscle mass, physiological cross-sectional area (PCSA), reduced PCSA (RPCSA), and fiber length (FL) are examined in the context of higher taxonomic group, as well as locomotor/postural and substrate preferences. Results show that muscle masses, PCSA, and RPCSA scale with positive allometry while FL scales with isometry indicating that larger primates have relatively stronger, but neither faster nor more flexible, forearms across the sample. When accounting for variation in body size, we found no statistically significant difference in architecture among higher taxonomic groups or locomotor/postural groups. However, we found that arboreal primates have significantly greater FL than terrestrial ones, suggesting that these species are adapted for greater speed and/or flexibility in the trees. These data may affect our interpretation of the mechanisms for variation in humeral morphology and provide information for refining biomechanical models of joint stress and movement in extant and fossil primates. Anat Rec, 301:484-495, 2018. © 2018 Wiley Periodicals, Inc.

Mechanical similarity across ontogeny of digging muscles in an Australian marsupial (Isoodon fusciventer)

“…However, as FL is proportional to shortening velocity, longer fibers shorten at greater velocity and therefore are capable of greater power generation, difference in FL between species have been linked to differences in function (Lieber & Ward, ; Rose, Nudds, & Codd, ). It has been suggested that positive scaling of FL is often associated with muscles for which there is a strong functional signal for particular behavior (i.e., differing diets, different locomotor styles) (Leischner et al, ). As such, we might expect that if larger Quenda are digging to a greater extent that FL should have increased with positive allometry.…”

“…This trade‐off is common, for example, in jaw muscles (Hartstone‐Rose, Perry, & Morrow, ) and hindlimbs (Marchi et al, ) as larger animals have different functional pressures than smaller species. The positive allometry in PCSA of the primate's forelimbs combined with isometry in FL, suggest that larger species rely on stronger forearms while smaller species have relatively faster and more flexible forearms (Leischner et al, ). A similar case was made for interspecific variation in the forelimb muscles of felids (Cuff et al, ); however, after a phylogenetic correction was performed, these results were not significant.…”

Extraordinary grip strength and specialized myology in the hyper‐derived hand of Perodicticus potto?

“…Leischner et al. ), or the collection of manual pressure distributions during gripping behaviors (e.g. Williams‐Hatala et al.…”

“…Eight taxa (including P. potto ) were dissected for the purposes of this study; the remaining data are derived from a previously published dataset (Leischner et al. ).…”

“… The presence of an asterisk (*) indicates the species that were dissected for this study and added to the Leischner et al. () dataset. For select individuals, muscle by muscle data were not available (indicated by a blank cell). …”