Analysis of the bite force and mechanical design of the feeding mechanism of the durophagous horn shark Heterodontus francisci

Abstract

Three-dimensional static equilibrium analysis of the forces generated by the jaw musculature of the horn shark Heterodontus francisci was used to theoretically estimate the maximum force distributions and loadings on its jaws and suspensorium during biting. Theoretical maximum bite force was then compared with bite forces measured (1) voluntarily in situ, (2) in restrained animals and (3) during electrical stimulation of the jaw adductor musculature of anesthetized sharks. Maximum theoretical bite force ranged from 128·N at the anteriormost cuspidate teeth to 338·N at the posteriormost molariform teeth. The hyomandibula, which connects the posterior margin of the jaws to the base of the chondrocranium, is loaded in tension during biting. Conversely, the ethmoidal articulation between the palatal region of the upper jaw and the chondrocranium is loaded in compression, even during upper jaw protrusion, because H. francisci's upper jaw does not disarticulate from the chondrocranium during prey capture. Maximum in situ bite force averaged 95·N for free-swimming H. francisci, with a maximum of 133·N. Time to maximum force averaged 322·ms and was significantly longer than time away from maximum force (212·ms). Bite force measurements from restrained individuals (187·N) were significantly greater than those from free-swimming individuals (95·N) but were equivalent to those from both theoretical (128·N) and electrically stimulated measurements (132·N). The mean mass-specific bite of H. francisci was greater than that of many other vertebrates and second highest of the cartilaginous fishes that have been studied. Measuring bite force on restrained sharks appears to be the best indicator of maximum bite force. The large bite forces and robust molariform dentition of H. francisci correspond to its consumption of hard prey.

Hard prey, soft jaws and the ontogeny of feeding mechanics in the spotted ratfishHydrolagus colliei

“…Linear regression was used to determine the predictive ability of head width and height with respect to bite force in H. colliei. Lastly, maximum bite forces and body masses from 14 species of fishes were compiled from the available literature (Hernandez & Motta 1997;Clifton & Motta 1998;Huber & Motta 2004;Korff & Wainwright 2004;Huber et al 2005Huber et al , 2006Huber 2006). When species data were available for a range of sizes, mean bite forces and masses were calculated.…”

“…Although the biomechanical model used in this analysis has accurately predicted maximum bite forces in numerous cartilaginous fishes (Huber & Motta 2004;Huber et al 2005;Huber 2006), theoretical maximum anterior bite force was significantly greater than tetanically stimulated anterior bite force. Hypothetically, this discrepancy could be due to a difference between the specific tensions of holocephalan and elasmobranch muscles, the latter of which was used to calculate maximum tetanic forces of the jaw adductors in H. colliei.…”

Morphology does not predict performance: jaw curvature and prey crushing in durophagous stingrays

“…Kolmann and Huber, 2009;Mara et al, 2010), anecdotal evidence suggests that the diversity of strategies for durophagy in elasmobranchs has only begun to be characterized. For example, the bonnethead shark (Sphyrna tiburo) and the horn shark (Heterodontus francisci) both purportedly use rapid, repeated jaw contractions to crush prey (Wilga and Motta, 2000;Huber et al, 2005;Mara et al, 2010), a method of cyclical loading to fatigue stiff exoskeletal materials that has also been documented in durophagous crabs (Kosloski and Allmon, 2015). In our study, we only tested the effects of constant rates of compression, but observations of myliobatid prey capture suggest that they may also use cyclical jaw movements in prey crushing (Sasko et al, 2006).…”

The ontogenetic scaling of bite force and head size in loggerhead sea turtles (Caretta caretta): implications for durophagy in neritic, benthic habitats

“…Similarly, bonnethead sharks (Sphyrna tiburo), which are durophagous crab specialists, demonstrate a maximum bite force of ~108N posteriorly and ~26N at the jaw tips (Mara et al, 2010). More impressive are horn sharks (Heterodontus francisci) and black tip sharks, for which the maximum theoretical bite force is reported as 128 and 423N, respectively, at the anterior teeth (Huber et al, 2005;Huber et al, 2006). These data suggest that loggerhead turtles newly recruited to neritic habitats have a bite capability great enough to allow them to consume a variety of smaller hard prey, and as individuals grow, larger and harder items become available, reducing competition.…”