The cranial biomechanics and feeding performance of Homo floresiensis

Homo floresiensis is a small-bodied hominin from Flores, Indonesia, that exhibits plesiomorphic dentognathic features, including large premolars and a robust mandible, aspects of which have been considered australopith-like. However, relative to australopith species, H. floresiensis exhibits reduced molar size and a cranium with diminutive midfacial dimensions similar to those of later Homo , suggesting a reduction in the frequency of forceful biting behaviours. Our study uses finite-element analysis to examine the feeding biomechanics of the H. floresiensis cranium. We simulate premolar (P 3 ) and molar (M 2 ) biting in a finite-element model (FEM) of the H. floresiensis holotype cranium (LB1) and compare the mechanical results with FEMs of chimpanzees, modern humans and a sample of australopiths (MH1, Sts 5, OH5). With few exceptions, strain magnitudes in LB1 resemble elevated levels observed in modern Homo . Our analysis of LB1 suggests that H. floresiensis could produce bite forces with high mechanical efficiency, but was subject to tensile jaw joint reaction forces during molar biting, which perhaps constrained maximum postcanine bite force production. The inferred feeding biomechanics of H. floresiensis closely resemble modern humans, suggesting that this pattern may have been present in the last common ancestor of Homo sapiens and H. floresiensis .

The role of the submentalis muscle in the feeding biomechanics of the marine toad, Rhinella marina

It is well documented that coordination of feeding behavior in anuran amphibians requires precise coordination of the jaw levators and depressors with the timing of the protraction of the tongue. (for review, see Nishikawa, 2000). However, the neuronal mechanism initiating and synchronizing this coordination is not well understood. In addition to the intermandibularis muscle and tongue musculature in the lower jaw, there is a small, transverse muscle at the tip of the jaw, the m. submentalis. Previous anatomical work has demonstrated the presence of muscle spindles in the submentalis, leading to the hypothesis that the activation of this muscle may provide proprioceptive information to aid in coordinating the feeding biomechanics in Rhinella marina. Here, we demonstrate that the submentalis likely acts as a ‘trigger’ to initiate the hypoglossal nerve to activate the tongue, and without feedback information from the muscle spindles of the submentalis, tongue protraction is compromised.

The role of the submentalis muscle in the feeding biomechanics of the marine toad, Rhinella marina

It is well documented that coordination of feeding behavior in anuran amphibians requires precise coordination of the jaw levators and depressors with the timing of the protraction of the tongue. (for review, see Nishikawa, 2000). However, the neuronal mechanism initiating and synchronizing this coordination is not well understood. In addition to the intermandibularis muscle and tongue musculature in the lower jaw, there is a small, transverse muscle at the tip of the jaw, the m. submentalis. Previous anatomical work has demonstrated the presence of muscle spindles in the submentalis, leading to the hypothesis that the activation of this muscle may provide proprioceptive information to aid in coordinating the feeding biomechanics in Rhinella marina. Here, we demonstrate that the submentalis likely acts as a ‘trigger’ to initiate the hypoglossal nerve to activate the tongue, and without feedback information from the muscle spindles of the submentalis, tongue protraction is compromised.