The giant Tyrannosaurs of the Late Cretaceous are some of the most iconic of all dinosaurs, but the group has more humble roots, originating as roughly human-sized predators in the Middle Jurassic, and only growing to large sizes in the last 20 million years of the Mesozoic. These early Tyrannosaurs have not been well understood until recently, when a series of new discoveries has greatly increased our understanding of the group's origin.
In a forthcoming paper in the journal Acta Palaeontologica Polonica Stephen Brusatte of the Division of Paleontology at the American Museum of Natural History and Roger Benson of the Department of Earth Sciences at the University of Cambridge carry out a systematic review of the early Tyrannosaurs, and as a result move one species into a new genus.
Stokesosaurus langhami was described in 2008 by Roger Benson, in a paper in the Journal of Vertebrate Paleontology, from a partial skeleton from the Late Jurassic of Dorset, England. It showed a number of similarities to Stokesosaurus clevelandi, an American species described in 1974. Subsequently a number of new species of Jurassic Tyranosaurs have been discovered, which share many of the same features as S. langhami and S. clevelandi, but which do not otherwise seem to be closely related, suggesting that these features were widespread within early members of the group. On the basis of this Brusatte and Benson conclude that there is no good reason to keep the species in the genus Stokesosaurus and assign it to a new genus, Juratyrant (Jurassic Tyrant).
(A) Right ilium of Juratyrant langhami (image reversed). (B) Left ilium of Stokesosaurus clevelandi. (C) Left ilium of Eotyrannus langhami. Arrows indicate position of lateral ridge, previously thought to be diagnostic of the genus Stokesosaurus. Scale bars are all 5 cm. From Brusatte and Benson (2012).
(A) Right pubis of Juratyrant langhami. (B) Left ischium of Juratyrant langhami. (C) Pubic peduncle of the left ilium of Stokesosaurus clevelandi. Scale bars are all 5 cm. From Brusatte and Benson (2012).