Estimating maximum bite performance in Tyrannosaurus rex using multi-body dynamics

Abstract

Bite mechanics and feeding behaviour in Tyrannosaurus rex are controversial. Some contend that a modest bite mechanically limited T. rex to scavenging, while others argue that high bite forces facilitated a predatory mode of life. We use dynamic musculoskeletal models to simulate maximal biting in T. rex. Models predict that adult T. rex generated sustained bite forces of 35 000-57 000 N at a single posterior tooth, by far the highest bite forces estimated for any terrestrial animal. Scaling analyses suggest that adult T. rex had a strong bite for its body size, and that bite performance increased allometrically during ontogeny. Positive allometry in bite performance during growth may have facilitated an ontogenetic change in feeding behaviour in T. rex, associated with an expansion of prey range in adults to include the largest contemporaneous animals.

Figure 1.

MDA model of adult T. rex. (a) Three-dimensional digitized skull with soft tissues reconstructed for mass and muscle properties (red, adductor mandibulae externus group; blue, adductor mandibulae posterior group; purple, pterygoideus group). (b) MDA model with joint centres (green circle), muscles (red cylinders), and ‘contact’ springs (blue spheres and cylinder) on the teeth in the initial simulation starting pose. (c) MDA model during sustained biting.

Figure 2.

(a) Bite force versus time for mid-jaw positions in the MDA models, showing an initial force peak representing the bite impact, before levelling off to record the sustained bite force (time normalized across models so that initiation of biting coincides). (b) Range in bite performance predictions for adult T. rex about the initial model for each parameter in the sensitivity analysis. Blue diamonds, initial model force; red squares, initial model velocity. (c) Mechanical advantage of jaw-closing muscles in the models. (d) Results of isometrically scaling all models to the mass of adult T. rex. White bars, force; grey bars, velocity. (e) Summed muscle force in the isometrically scaled models. (f) Comparison of biting forces predicted in this study with some of the largest values in the literature for terrestrial vertebrates ([–8,12,13], grey bars are values from previous studies; white bars are from this analysis). (a,c) Lines: black, human; green, juvenile Alligator; red, adult Alligator; yellow, Allosaurus; blue, adult T. rex; purple, juvenile T. rex.