Re-description of 'Steneosaurus' obtusidens Andrews, 1909, an unusual macrophagous teleosaurid crocodylomorph from the Middle Jurassic of England

Johnson, Michela M., Young, Mark T., Steel, Lorna, Foffa, Davide, Smith, Adam S., Hua, Stéphane, Havlik, Philipe, Howlett, Eliza A. and Dyke, Gareth (2018) Re-description of 'Steneosaurus' obtusidens Andrews, 1909, an unusual macrophagous teleosaurid crocodylomorph from the Middle Jurassic of England. Zoological Journal of the Linnean Society, 182 (2), 385-418. (doi:10.1093/zoolinnean/zlx035).

Abstract

Teleosaurids were a clade of crocodylomorphs that attained near-global distribution during the Jurassic Period. Within Teleosauridae, one particular sub-clade of durophagous/macrophagous taxa achieved large body sizes and were apex predators in shallow marine environments during the Late Jurassic and Early Cretaceous in Europe and around the coast of the Tethys Seaway. Unfortunately, the origins of this clade are still poorly understood. 'Steneosaurus' obtusidens is a little-studied macrophagous species from the Oxford Clay Formation (Callovian, Middle Jurassic) of the UK and near Migné-les-Lourdines (Middle Callovian) in France. Despite being considered a sister taxon of the Late Jurassic taxon Machimosaurus, the taxonomy of 'S.' obtusidens remains unclear. Although three different synonymies have been proposed (variously a subjective synonym of other taxa), these taxonomic hypotheses have not been based on detailed anatomical comparisons and thus have not been tested. Here, we re-describe the holotype of 'S.' obtusidens, demonstrate that it is indeed a valid taxon, restrict the referred specimens to a fragmentary skeleton, nearly complete skull, and partial rostrum, and establish a new monotypic genus, Lemmysuchus. Our re-description reveals five autapomorphies for Lemmysuchus obtusidens and nine apomorphic characters that support the tribe Machimosaurini (Lemmysuchus + Machimosaurus).

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