4.5 Editorial Material

Dentary groove morphology does not distinguish 'Nanotyrannus' as a valid taxon of tyrannosauroid dinosaur. Comment on: Distribution of the dentary groove of theropod dinosaurs: Implications for theropod phylogeny and the validity of the genus Nanotyrannus Bakker et al., 1988

Journal

CRETACEOUS RESEARCH
Volume 65, Issue -, Pages 232-237

Publisher

ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.cretres.2016.02.007

Keywords

Nanotyrannus; Tyrannosaurus; Tyrannosauroid; Dinosaur; Theropod; Ontogeny

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There has been considerable debate about whether the controversial tyrannosauroid dinosaur 'Nanotyrannus lancensis' from the uppermost Cretaceous of North America is a valid taxon or a juvenile of the contemporaneous Tyrannosaurus rex. In a recent Cretaceous Research article, Schmerge and Rothschild (2016) brought a new piece of evidence to this discussion: the morphology of the dentary groove, a depression on the lateral surface of the dentary that houses neurovascular foramina. They argued that an alleged 'Nanotyrannus' specimen, which possesses a groove, cannot be referable to Tyrannosaurus rex, which they considered as lacking the groove, and they hypothesized that 'Nanotyrannus' is closely related to albertosaurine tyrannosauroids, which also are said to possess the groove. However, we show that the groove is a widespread feature of tyrannosauroids that is present in T. rex and many other specimens, and that it is an ontogenetically variable feature that changes from a sharp, deeply-impressed groove to a shallower sulcus as an individual matures. As a result, the presence or absence of a dentary groove does not clarify the validity of 'Nanotyrannus' or its phylogenetic position among tyrannosauroids. We consider it most parsimonious that 'Nanotyrannus' specimens belong to juvenile T. rex. (C) 2016 Elsevier Ltd. All rights reserved.

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