Comparisons of specimens attributed to Tyrannosaurus: One or three species ?

Abstract

Abstract Tyrannosaurus was a massive carnivorous dinosaur which existed for roughly 2 million years in North America prior to its extinction at the end of the Cretaceous Period. It was recently proposed by Gregory Paul and colleagues that fossil specimens historically attributed to the species T. rex represent three species, not one. This conclusion reflects an essential problem in palaeontology of defining species and recognizing species boundaries. In this study we test the T1 hypothesis that specimens attributed to T. imperator, T. regina, and T. rex represent the single species T. rex (recognising that, per the International Code of Zoological Nomenclature the nomen T. rex (1905) has precedence over T. regina and T. imperator). Based on an analysis of skull and postcranial dimensions of three iconic Tyrannosaurus specimens and application of a probabilistic morphometric definition of species as described by Thackeray & Dykes, our results indicate a high probability of conspecificity, thus supporting the T1 hypothesis.