Читать книгу Hadrosaurs - David A. Eberth - Страница 100

“Trachodon cantabrigiensis” and ‘Iguanodon’ hillii are poorly known ornithopod taxa from the “middle” Cretaceous of England that were both named on the basis of a single isolated tooth. The holotype of “T.” cantabrigiensis was collected from the Cambridge Greensand Member of the Melbury Marly Chalk Formation (Cenomanian) and was reworked from late Albian deposits, while that of ‘I.’ hillii is from the slightly younger Totternhoe Stone Member of the Zig Zag Chalk Formation (middle Cenomanian). Both taxa have been suggested to represent hadrosaurids, and if correctly identified would form the earliest-known records of this predominantly latest Cretaceous dinosaur clade. Here we provide redescriptions of these teeth, and evaluate their morphology with reference to the phylogenetic distributions of hadrosauroid dental characters. In addition, we incorporate “T. cantabrigiensis” into a morphometric analysis of iguanodontian tooth crown shape. Results indicate that although both taxa share many features in common with hadrosaurids, neither can be referred to this clade. Nevertheless, both taxa appear to nest in a grade of hadrosauroid taxa, including Bactrosaurus and Telmatosaurus, which are among the closest relatives of hadrosaurids. Consequently, these isolated European records need to be considered when discussing the paleobiogeography of hadrosaurid origins.