Sagittal suture strain in capuchin monkeys (Sapajus and Cebus) during feeding

Abstract

Objectives: Morphological variation in cranial sutures is used to infer aspects of primate feeding behavior, including diet, but strain regimes across sutures are not well documented. Our aim is to test hypotheses about sagittal suture morphology, strain regime, feeding behavior, and muscle activity relationships in robust Sapajus and gracile Cebus capuchin primates.Materials and Methods: Morphometrics of sinuosity in three regions of the sagittal suture were compared among museum specimens of Sapajus and Cebus, as well as in robust and gracile lab specimens. In vivo strains and bilateral electromyographic (EMG) activity were recorded from these regions in the temporalis muscles of capuchin primates while they fed on mechanically-varying foods.Results: Sapajus and the anterior suture region exhibited greater sinuosity than Cebus and posterior regions. In vivo data reveal minor differences in strain regime between robust and gracile phenotypes but show higher strain magnitudes in the middle suture region and higher tensile strains anteriorly. After gage location, feeding behavior has the most consistent and strongest impact on strain regime in the sagittal suture. Strain in the anterior suture has a high tension to compression ratio compared to the posterior region, especially during forceful biting in the robust Sapajus-like individual.Discussion: Sagittal suture complexity in robust capuchins likely reflects feeding behaviors associated with mechanically challenging foods. Sutural strain regimes in other anthropoid primates may also be affected by activity in feeding muscles.

Gape drives regional variation in temporalis architectural dynamics in tufted capuchins

“…As reported in Byron et al . [84], the working-side SPT peaks significantly earlier than the balancing-side SMT and SPT, and the working-side SMT and superficial masseter (all p < 0.05; electronic supplementary material, figure S1 and table S4) in rank order comparisons. These comparisons also suggest the working-side SAT peaks significantly earlier than the balancing-side SPT, which peaks significantly later than the balancing-side SAT (both p < 0.05; electronic supplementary material, table S4).…”

“…The EMG data were collected using indwelling bipolar fine-wire electrodes following procedures described in Byron et al . [84]. Briefly, the ends of two EMG wires were threaded into a 25-gauge or smaller hypodermic needle, then folded against the needle shaft to create a hook.…”

The biomechanics of chewing and suckling in the infant: A potential mechanism for physiologic metopic suture closure

“…As we found in our human models, Behrent et al found the sagittal suture to be placed under medial-laterally directed tension during chewing in macaques, but the findings are limited due to the use of single-element gauges [ 33 ]. The nonhuman primate for which the best in vivo data are available is the capuchin monkey Cebus/Sapajus from Byron et al [ 73 ]. In vivo strains were measured at three sites along the sagittal suture in adult capuchins using rosette strain gages.…”

“…They also show that the sagittal suture is not loaded in purely laterally directed tension, as is often assumed, but is subjected to torsion or twisting, probably due to asymmetrical activity of the temporalis muscle. However, the data show that tensile strains are larger at the front of the sagittal suture than the back, and this is associated with greater sinuosity in the anterior suture than more posteriorly [ 74 ]. Conflicting data exists for rat models, such as those reported by Shibazaki et al, who measured the interfrontal suture to be in compression during chewing [ 31 ].…”