Abstract
Lanzhousaurus magnidens, a large non-hadrosauriform iguanodontian dinosaur from the Lower Cretaceous Hekou Group of Gansu Province, China has the largest known herbivorous dinosaur teeth. Unlike its hadrosauriform relatives possessing tooth batteries of many small teeth, Lanzhousaurus utilized a small number (14) of very large teeth (~10 cm long) to create a large, continuous surface for mastication. Here we investigate the significance of Lanzhousaurus in the evolutionary history of iguanodontian-hadrosauriform transition by using a combination of stable isotope analysis and CT imagery. We infer that Lanzhousaurus had a rapid rate of tooth enamel elongation or amelogenesis at 0.24 mm/day with dental tissues common to other Iguanodontian dinosaurs. Among ornithopods, high rates of amelogenesis have been previously observed in hadrosaurids, where they have been associated with a sophisticated masticatory apparatus. These data suggest rapid amelogenesis evolved among non-hadrosauriform iguanodontians such as Lanzhousaurus, representing a crucial step that was exapted for the evolution of the hadrosaurian feeding mechanism.
Highlights
Of the holotype of Lanzhousaurus to answer these questions
Lanzhousaurus magnidens was discovered above the basal thick conglomerates at the base of a channel sandstone that cuts through a series of calcic paleosols
Phosphate oxygen isotopic composition (δ18Op) of Lanzhousaurus has a cyclic pattern when plotted relative to sample location along the long axis of the tooth
Summary
The ultimate test of tooth growth rate would be to thin section the teeth and count lines of von Ebner. Less damage is incurred on these unique teeth by using stable isotopic analysis, allowing us to infer tooth elongation (rather than growth rate). We use stable isotope data to infer rapid amelogenesis for Lanzhousaurus. We test these inferred amelogenesis rates using CT imaging, which revealed long-period or Andresen lines[7,8] whose thickness is consistent with the rapid rates of amelogenesis derived from stable isotope patterns. In an attempt to resolve the relationship between amelogenesis rate and tooth growth rate we conducted preliminary CT imaging of the sampled teeth
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