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.
Highlights
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
We evaluate the biomechanical behaviour of otodontid shark teeth by means of Finite Element Analysis (FEA)
Stress is distributed along the center of the crown in teeth with crowns approximating an equilateral or isosceles triangular morphology, such as the anterior teeth of O. chubutensis and O. megalodon
Summary
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, leading to the evolution of titanic body sizes in the most recent forms (including the emblematic Otodus megalodon). Possessing thick layers of blubber, these taxa would have represented ideal prey for large-sized mesotherms to meet the metabolic demands of their active lifestyles[10,11,12] Within this scenario, the earliest otodontids subsisted on comparatively small prey items, presumably fishes, whereas the largest and more recent species, including O. megalodon, consumed larger marine m ammals[8,9,13,14]. Puncture was simulated under life-size absolute force estimates (i.e., bite forces that each species would have exerted in life considering their estimated body size) and scaled forces (i.e., force magnitudes scaled to maintain a constant force to surface area ratio across all models to account for morphology o nly32); and draw was simulated under scaled forces only
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