Evolution Of Jaw Mechanisms In Ornithopod Dinosaurs PDF Download

Understanding the feeding mechanisms and diet of ornithopod dinosaurs is fundamental to understanding their role in Late Cretaceous ecosystems. Current hypotheses of feeding behaviour are based on functional morphology, and testing these is problematic. Microscopic scratches, microwear, that form on teeth in vivo during feeding are known to record the relative movement of the tooth rows and to capture evidence of tooth-food interactions; however, their applicability to ornithischian dinosaurs has not been tested. The development of a fast non-abrasive and residue free method for the removal of resistant consolidant, along with a safe, rapid technique for replicating tooth surfaces was the first step towards assessing the suitability of quantitative tooth microwear analysis techniques for dinosaur teeth. An evaluation of appropriate statistical analysis methods followed, identifying suitably stringent tests for the analysis of variance in the multi-modal directional microwear data. Analysis of microwear orientation in Iguana iguana provided direct evidence for relative motion of the jaws. Microwear from the basal ornithischian Lesothosaurus diagnosticus revealed three distinct sets of scratches in different orientations that were comparable to those of I. iguana, confirming the isognathic, near-vertical, simple adduction predicted for this dinosaur. Results from the basal ornithopod Hypsilophodon foxii indicate a propalinal translation of the lower jaw during feeding and provide strong support for muscular cheeks, whilst those from the hadrosaurid Edmontosaurus indicate a near-vertical posterodorsal power stroke with a secondary propalinal action and support the presence of a pleurokinetic hinge. Analysis of a range of hadrosaurid taxa found that three differing mastication methods existed, potentially diet related. Furthermore, microwear suggests that here is no significant difference in the jaw mechanics between iguanodontians and hadrosaurids. The results demonstrate that microwear has great potential for unravelling the mystery of dinosaur feeding and identifying key stages in the evolution of jaw mechanics in ornithopods.