The first definitive Middle Jurassic atoposaurid (Crocodylomorpha, Neosuchia), and a discussion on the genusTheriosuchus.
Atoposaurids were a clade of semiaquatic crocodyliforms known from the Late Jurassic to the latest Cretaceous. Tentative remains from Europe, Morocco, and Madagascar may extend their range into the Middle Jurassic. Here we report the first unambiguous Middle Jurassic (late Bajocian-Bathonian) atoposaurid: an anterior dentary from the Isle of Skye, Scotland, UK. A comprehensive review of atoposaurid specimens demonstrates that this dentary can be referred toTheriosuchusbased on several derived characters, and differs from the five previously recognized species within this genus. Despite several diagnostic features, we conservatively refer it toTheriosuchussp., pending the discovery of more complete material. As the oldest known definitively diagnostic atoposaurid, this discovery indicates that the oldest members of this group were small-bodied, had heterodont dentition, and were most likely widespread components of European faunas. Our review of mandibular and dental features in atoposaurids not only allows us to present a revised diagnosis ofTheriosuchus, but also reveals a great amount of variability within this genus, and indicates that there are currently five valid species that can be differentiated by unique combinations of dental characteristics. This variability can be included in future broad-scale cladistics analyses of atoposaurids and closely related crocodyliforms, which promise to help untangle the complicated taxonomy and evolutionary history of Atoposauridae.  © 2015 The Authors. Zoological Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of The Linnean Society of London.
School of GeoSciences, Grant Institute, The King's BuildingsUniversity of EdinburghJames Hutton RoadEdinburghEH9 3FEUK; School of Ocean and Earth Science, National Oceanography CentreUniversity of SouthamptonEuropean WaySouthamptonSO14 3ZHUK.
Mark T
0000-0002-7263-6505
MT
Young
Department of Earth Science and Engineering Imperial College London London SW6 2AZ UK.
Jonathan P
JP
Tennant
School of GeoSciences, Grant Institute, The King's BuildingsUniversity of EdinburghJames Hutton RoadEdinburghEH9 3FEUK; National Museums ScotlandChambers StreetEdinburghEH1 1JFUK.
Stephen L
SL
Brusatte
School of GeoSciences, Grant Institute, The King's Buildings University of Edinburgh James Hutton Road Edinburgh EH9 3FE UK.
Thomas J
TJ
Challands
School of GeoSciences, Grant Institute, The King's BuildingsUniversity of EdinburghJames Hutton RoadEdinburghEH9 3FEUK; National Museums ScotlandChambers StreetEdinburghEH1 1JFUK.
Nicholas C
NC
Fraser
The Hunterian University of Glasgow University Avenue Glasgow G12 8QQ UK.
Neil D L
ND
Clark
Staffin Museum 6 Ellishadder Staffin Isle of Skye IV51 9JE UK.
Dugald A
DA
Ross
Atoposauridae; Bathonian; Crocodyliformes; Scotland; Valtos Sandstone Formation