Abstract

The family Hadrosauridae as originally named by E. D. Cope in 1869 is reevaluated using shared derived characters, and found to exhibit a dichotomy suggesting a diphyletic origin. The newly defined Hadrosauridae is found to share a number of derived characters with the genus Iguanodon, whereas the newly defined Lambeosauridae shares a number of derived characters with the genus Ouranosaurus. The newly defined families are defined exclusively with shared derived characters.

Introduction

In 1869, Edward Drinker Cope proposed the family name Hadrosauridae for the herbivorous bipedal dinosaurs having several vertical rows of teeth forming a dental battery. Although there was some discussion in later years as to whether or not the family should be called the Trachodontidae (Lydekker 1888; Marsh 1890), the Hadrosauridae has been retained. For nearly a century, all of the “duckbilled” dinosaurs have been considered a single family, broken down into a variety of subfamilies (Brown 1914; Lambe 1918; Parks 1923; Lull and Wright 1942; Sternberg 1954). Lull and Wright (1942) give the family characters of the Hadrosauridae as follows:

Bipedal, unarmored dinosaurs, with a complicated dental battery consisting of many rows of teeth whose enamelled crowns, at least in the dentary, form a tessellated pavement. Individual teeth enamelled on one face only. Premaxillae edentulous and, together with the predentary, forming a more or less broadened, duck-like beak. Rear of skull either flat, or crested in varying degree.