Biomechanical insights into the dentition of megatooth sharks (Lamniformes: Otodontidae)

Abstract

The evolution of gigantism in extinct otodontid sharks was paralleled by a series of drastic modifications in their dentition including widening of the crowns, loss of lateral cusplets, and acquisition of serrated cutting edges. These traits have generally been interpreted as key functional features that enabled the transition from piscivory to more energetic diets based on marine mammals, ultimately leading to the evolution of titanic body sizes in the most recent forms (including the emblematic Otodus megalodon). To investigate this hypothesis, we evaluate the biomechanics of the anterior, lateral, and posterior teeth of five otodontid species under different loading conditions by using two-dimensional finite element analysis. Stress distribution patterns are remarkably similar among all models under puncture and draw (i.e., when subjected to vertical and lateral forces, respectively). Contrary to expectation, higher average stress values are detected under both loading scenarios in more recent species. Altogether, this suggests little correlation between tooth morphology and key aspects of biomechanical behaviour in otodontids, making it difficult to frame the morphological trend of their dentitions within an adaptive scenario. We propose that this pattern most likely emerged as a non-functional by-product of heterochronic processes driven by selection towards larger body sizes.

The efficacy of computed tomography scanning versus surface scanning in 3D finite element analysis

“…Once we calculated mean von Mises stress values for all models, we also calculated the mesh-weighted arithmetic mean (MWAM) von Mises stress value for each model using R ( R Core Team, 2021 ). This method accounts for element size differences within non-uniform meshes and has been used in previous biomechanical studies of vertebrate palaeobiology ( Marcé-Nogué et al, 2016 ; Morales-García et al, 2019 ; Ballell & Ferrón, 2021 ). It can reduce discrepancies in von Mises stress between CT scanned models and surface scanned models.…”

Taking a stab at modelling canine tooth biomechanics in mammalian carnivores with beam theory and finite-element analysis

“…Single summary values of von Mises stress or strains, like average von Mises stress [ 29 , 32 , 48 , 49 ] or strains [ 50 ] and maximum von Mises stress [ 29 , 52 ] or strains [ 51 ] and median von Mises stress [ 57 ] have been used in previous research as indicators of biomechanical performance in a comparative context [ 48 ], or to undertake subsequent statistical analyses [ 15 , 32 , 51 ]. While such numerical comparisons defeat the primary purpose of FEA, modelling the distribution of stresses and strain across a complex structure, they can still yield valuable insights in a simplified comparative context.…”

“…To simulate pulling (PULL), force was applied in the anterior direction (negative z axis), and to simulate shaking (SHAKE), force was applied in the lingual direction (negative y axis) of the tooth (figure 2b). While our loading conditions are approximations of the feeding behaviours due to being static and unidirectional simulations, we have used the terms PULL and SHAKE for consistency with previous studies [30,32,[48][49][50][51][52]. We chose to simulate these behaviours at 50% and 90% of the tooth height to vary the amount of tooth embedded in the prey giving four loading conditions (PULL 50%, PULL 90%, SHAKE 50% and SHAKE 90%).…”

“…For consistency with BTA, a compressive force of 300 N was applied across all loading conditions. Again, although our loading conditions are approximations of the feeding behaviours, we have used the terms BITE, PULL and SHAKE for consistency with previous studies [30,32,[48][49][50][51][52].…”

Cenozoic megatooth sharks occupied extremely high trophic positions

“…Its large, triangular, serrated teeth [e.g., ( 2 )] and bite marks in fossil cetacean and pinniped bones suggest that adult O. megalodon had a diet of marine mammals [( 28 – 30 ) and references therein]. While this evidence is compelling, the morphological trend observed in the megatooth shark lineage may not necessarily suggest any possible dietary preference or shift ( 31 ), and bite marks reflect brief events that may not represent the overall diet of O. megalodon . A high trophic level for O. megalodon has been inferred from low δ 44/42 Ca values of two Pliocene teeth ( 7 ); however, this evidence is so far limited in scope with respect to sample size, temporal span, and spatial distribution.…”