What is Geosaurus? Redescription of Geosaurus giganteus (Thalattosuchia: Metriorhynchidae) from the Upper Jurassic of Bayern, Germany

Authors: YOUNG, MARK THOMAS; DE ANDRADE, MARCO BRANDALISE

Source: Zoological Journal of the Linnean Society, Volume 157, Number 3, November 2009 , pp. 551-585(35)

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Abstract:

The holotype and referred specimens of Geosaurus giganteus, a metriorhynchid crocodile from the Tithonian (Upper Jurassic) of Germany, is redescribed, along with a historical overview of the genus and species. This taxon is unique among metriorhynchids as its serrated, strongly lateromedially compressed dentition is arranged as opposing blades, suggesting it was adapted to efficiently slice through fleshy prey. A new phylogenetic analysis of Crocodylomorpha is presented, which finds G. giganteus to be nested within what is currently considered Dakosaurus, whereas the other species currently assigned to Geosaurus form a clade with Enaliosuchus and the holotype of Cricosaurus. The phyletic relationship of G. giganteus with other metriorhynchids indicates that the current definition of the genus Geosaurus is polyphyletic, and that the inclusion of subsequent longirostrine species to this genus is in error. The re-analysis presented herein demonstrates Geosaurus to be composed of three species sensu stricto. The appropriate taxonomic amendments to the Metriorhynchidae are also provided.

Keywords: Cricosaurus; Crocodylia; Dakosaurus; Mörnsheim Formation; Metriorhynchidae; phylogeny; Rhacheosaurus

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1096-3642.2009.00536.x

Affiliations: 1: Department of Earth Sciences, University of Bristol, Wills' Memorial Building, Queen's Road, Bristol, BS8 1RJ, UK

Publication date: 2009-11-01