Individual variation in the postcranial skeleton of the Early Cretaceous Iguanodon bernissartensis (Dinosauria: Ornithopoda)

At the end of nineteenth century, approximately thirty nearly complete skeletons of the ornithopod dinosaur Iguanodon bernissartensis were discovered in Lower Cretaceous deposits in Bernissart (Belgium). Because most of the specimens are approximately the same size, they offer a unique opportunity for studying individual variation (i.e., differences among individuals of the same or roughly the same age) in iguanodontians. Here, we report the results of a study combining both morphometric and visual analyses of the postcranial skeleton of the Bernissart specimens. We found significant individual variation in the morphology of the axis, sacrum, caudal vertebrae, scapula, humerus, pollex, ilium, ischium, femur, and tibia. No definitive evidence of sexual dimorphism was identified in I. bernissartensis. Individual variation in I. bernissartensis has significant implications for phylogenetic and ontogenetic studies as well as for evaluating diagnostic characters in Iguanodon and other iguanodontians. For example, the status of the basal styracosternan 'Delapparentia turolensis' from the lower Barremian of Spain is discussed; given the individual variation in the postcranial skeleton of I. bernissartensis, it is in fact impossible to distinguish 'Delapparentia' from Iguanodon species based on the available material.