Ornithopod dinosaurs evolved numerous craniodental innovations related to herbivory.
Nonetheless, the relationship between occlusion, tooth wear rate, and tooth replacement
rate has been neglected. Here, we reconstruct tooth wear rates by measuring tooth
replacement rates and tooth wear volumes, and document their dental microwear. We
demonstrate that total tooth volume and rates of tooth wear increased steadily during
ornithopod evolution, with deeply-nested taxa wearing up to 3360 mm 3 of tooth volume/day.
Increased wear resulted in asymmetric tooth crown formation with uneven von Ebner
line increment width by the Late Jurassic, and in faster tooth replacement rates in
multiple lineages by the mid-Cretaceous. Microwear displays a contrasting pattern,
with decreasing complexity and pit percentages in deeply-nested and later-occurring
taxa. We hypothesize that early ornithopods were browsers and/or frugivores but deeply
nested iguanodontians were bulk-feeders, eating tougher, less nutritious plants; these
trends correlate with increasing body mass and longer gut passage times.
