A simple morphological predictor of bite force in rodents

Bite force was quantified for 13 species of North American rodents using a piezo-resistive sensor. Most of the species measured (11) formed a tight relationship between body mass and bite force (log 10(bite force)=0.43(log 10(body mass))+0.416; R ²>0.98). This high correlation exists despite the ecological (omnivores, grazers and more carnivorous) and taxonomic (Cricetidae, Heteromyidae, Sciuridae and Zapodidae) diversity of species. Two additional species, Geomys bursarius (Geomyidae) and a Sciurus niger (Sciuridae), bit much harder for their size. We found a simple index of strength based on two measurements of the incisor at the level of the alveolus ( Z_i =((anterior-posterior length)²× (medial-lateral width))/6) that is highly predictive of bite force in these rodents (R²>0.96). Z_i may be useful for prediction of bite force (log10 (Bite Force)=0.566log10 ( Z_i )+1.432) when direct measurements are not available.     

Disparity between Feeding Performance and Predicted Muscle Strength in the Pharyngeal Musculature of Black Drum, Pogonias cromis (Sciaenidae)

Synopsis Pogonias cromis, black drum, is the largest durophagous sciaenid and feeds almost exclusively on hard-shelled bivalves and gastropods using powerful pharyngeal jaws. I estimated pharyngeal jaw bite forces used to crush live molluscs during feeding trials from juvenile and young adult Pogonias cromis, and they are the highest yet documented for bony fishes. Crushing ability in P. cromis scaled with strong positive allometry suggesting large adult fish may have one of the strongest bites among vertebrates. Physiological estimates of pharyngeal muscle strength derived from muscle cross sectional area accounted for only half of the force generated during actual feeding performance trials. The significant disparity between feeding performance and pharyngeal muscle strength in P. cromis indicates the presence of novel biomechanical linkages that enhance crushing ability for feeding on hard-shelled molluscs. I present a biomechanical model in which the lower pharyngeal jaw architecture of P. cromis emulates a second class lever mechanism that can amplify muscle forces transmitted to the shell of the prey.     

Omnivory in lacertid lizards: adaptive evolution or constraint?

Feeding specializations such as herbivory are an often cited example of convergent and adaptive evolution. However, some groups such as lizards appear constrained in the evolution of morphological specializations associated with specialized diets. Here we examine whether the inclusion of plant matter into the diet of omnivorous lacertid lizards has resulted in morphological specializations and whether these specializations reflect biomechanical compromises as expected if omnivores are constrained by functional trade-offs. We examined external head shape, skull shape, tooth structure, intestinal tract length and bite performance as previous studies have suggested correlations between the inclusion of plants into the diet and these traits. Our data show that omnivorous lacertid lizards possess modifications of these traits that allow them to successfully exploit plant material as a food source. Conversely, few indications of a compromise phenotype could be detected, suggesting that the evolution towards herbivory is only mildly constrained by functional trade-offs.     

Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli, an ancient apex predator

Placoderms are a diverse group of armoured fishes that dominated the aquatic ecosystems of the Devonian Period, 415-360 million years ago. The bladed jaws of predators such as Dunkleosteus suggest that these animals were the first vertebrates to use rapid mouth opening and a powerful bite to capture and fragment evasive prey items prior to ingestion. Here, we develop a biomechanical model of force and motion during feeding in Dunkleosteus terrelli that reveals a highly kinetic skull driven by a unique four-bar linkage mechanism. The linkage system has a high-speed transmission for jaw opening, producing a rapid expansion phase similar to modern fishes that use suction during prey capture. Jaw closing muscles power an extraordinarily strong bite, with an estimated maximal bite force of over 4400 N at the jaw tip and more than 5300 N at the rear dental plates, for a large individual (6 m in total length). This bite force capability is the greatest of all living or fossil fishes and is among the most powerful bites in animals.     

Does whole‐organism performance constrain resource use? A community test with desert lizards

Discovering the mechanisms by which communities of co‐existing species exist has proven to be one of the greatest challenges for evolutionary ecologists. A recent perspective emphasizes the role of functional traits, such as whole‐organism performance, as key limiting factors in the evolution of communities, yet few studies have examined this possibility. We examine how bite force and morphology influence the ability of ten lizard species in a single community to access insect prey, as defined by prey type and prey hardness. We gathered over 3 years of data from a desert lizard community comprised of ten species and found significant variation among species for bite force and prey hardness, as well as significant differences in performance and niche breadth for each species. In general, higher levels of absolute bite force broadens resource accessibility (sizes of prey), and does not generally result in a reduced ability to access smaller prey. For example, large lizard species that are hard biters can still consume soft prey. On the other hand, small lizard species that are weak biters are more limited in their ability to access hard prey, although the overall decline in resource accessibility is modest. Our findings highlight how functional traits can influence which species can access key resources within a community of similar species. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●● , ●●–●●.     

The shrew tamed by Wolff's law: Do functional constraints shape the skull through muscle and bone covariation?

Bone is a highly plastic tissue that reflects the many potential sources of variation in shape. Here, we focus on the functional aspects of bone remodeling. We choose the skull for our analyses because it is a highly integrated system that plays a fundamental role in feeding and is thus, likely under strong natural selection. Its principal mechanical components are the bones and muscles that jointly produce bite force and jaw motion. Understanding the covariations among these three components is of interest to understand the processes driving the evolution of the feeding apparatus. In this study, we quantitatively and qualitatively compare interactions between these three components in shrews from populations known to differ in shape and bite force. Bite force was measured in the field using a force transducer and skull shape was quantified using surface geometric morphometric approaches based on µCT‐scans of the skulls of same individuals. The masseter, temporalis, pterygoideus, and digastricus muscles of these individuals were dissected and their cross sectional areas determined. Our results show strong correlations between bite force and muscle cross sectional areas as well as between bite force and skull shape. Moreover, bite force explains an important amount of skull shape variation. We conclude that interactions between bone shape and muscle characteristics can produce different morpho‐functional patterns that may differ between populations and may provide a suitable target for selection to act upon. J. Morphol. 276:301–309, 2015. © 2014 Wiley Periodicals, Inc.