Ontogeny of bite force in a validated biomechanical model of the American alligator

Abstract

Three-dimensional computational modeling offers tools with which to investigate forces experienced by the skull during feeding and other behaviors. American alligators (Alligator mississippiensis) generate some of the highest measured bite forces among extant tetrapods. A concomitant increase in bite force accompanies ontogenetic increases in body mass, which has been linked with dietary changes as animals increase in size. Because the flattened skull of crocodylians has substantial mediolaterally oriented muscles, crocodylians are an excellent model taxon in which to explore the role of mediolateral force components experienced by the feeding apparatus. Many previous modeling studies of archosaur cranial function focused on planar analysis, ignoring the mediolateral aspects of cranial forces. Here, we used three-dimensionally accurate anatomical data to resolve 3D muscle forces. Using dissection, imaging and computational techniques, we developed lever and finite element models of an ontogenetic series of alligators to test the effects of size and shape on cranial loading and compared estimated bite forces with those previously measured in vivo in A. mississippiensis. We found that modeled forces matched in vivo data well for intermediately sized individuals, and somewhat overestimated force in smaller specimens and underestimated force in larger specimens, suggesting that ontogenetically static muscular parameters and bony attachment sites alone cannot account for all the variation in bite force. Adding aponeurotic muscle attachments would likely improve force predictions, but such data are challenging to model and integrate into analyses of extant taxa and are generally unpreserved in fossils. We conclude that anatomically accurate modeling of muscles can be coupled with finite element and lever analyses to produce reliable, reasonably accurate estimate bite forces and thus both skeletal and joint loading, with known sources of error, which can be applied to extinct taxa.

Convergence and functional evolution of longirostry in crocodylomorphs

“…In these cases, attachment sites were identified in the digital Pelagosaurus model and inferred by homology with extant crocodilians (Holliday & Witmer ; Sellers et al . ).…”

“…The cartilago transiliens, a cartilaginous element that acts as the origin and insertion point of some jaw adductors (Tsai & Holliday ), was not modelled here, following previous muscle reconstructions in extant crocodilians (Holliday & Witmer ; Sellers et al . ). Instead, the mPSTs and the mIM were considered as a single muscle complex (mPSTs) extending from the mPSTs origin site to the mIM insertion surface.…”

“…; Sellers et al . ) and a muscle reconstruction of the teleosaurid thalattosuchian Steneosaurus brevior (Mueller‐Töwe ) served as guides to identify muscle attachment sites in Pelagosaurus . Three additional Pelagosaurus specimens, ranging from juveniles to adults, in the BRLSI (M1416, M1418 and M1420) were also examined, in addition to the study specimen.…”

Reproductive phenotype predicts adult bite‐force performance in sex‐reversed dragons (Pogona vitticeps)

“…In contrast to the situation in P. vitticeps , sex‐reversed female mice (X*Y) were found to have greater bite‐force performance than both concordant females and males (Ginot et al, 2017). However, as in P. vitticeps , the greater bite force is associated with greater head size, thus highlighting the close relationship between head size and bite force (related to jaw muscle physiological cross‐sectional area, e.g., Erickson et al, 2003; Gans, 1982; Gröning et al, 2013; Santana et al, 2010; Sellers et al, 2017). The results for both taxa hint at the diversity of phenotypic responses to sex reversal that may exist in nature.…”

“…To test the scaling of bite force for allometry across ontogeny (including juveniles and adults) for each of the three groups (ZZf, ZWf, and ZZm) we fitted linear models of log10‐transformed bite force as a function of log10‐transformed SVL, mass, and each of the head dimensions to each group separately (Table 3). Maximum bite force performance should scale isometrically with the cross‐sectional area of the jaw muscles contributing to the bite (Erickson, Lappin, & Vliet, 2003; Gans, 1982; Gröning et al, 2013; Santana, Dumont, & Davis, 2010; Sellers, Middleton, Davis, & Holliday, 2017). Therefore, if bite force performance in Pogona scales isometrically with the size it should scale to the square of linear measurements (e.g., SVL) with a slope of 2.000 and to the two‐thirds power of volumes (e.g., body mass) with a slope of 0.667 (Erickson et al, 2003).…”