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The first definitive Middle Jurassic atoposaurid (Crocodylomorpha, Neosuchia), and a discussion on the genus Theriosuchus

The first definitive Middle Jurassic atoposaurid (Crocodylomorpha, Neosuchia), and a discussion on the genus Theriosuchus
The first definitive Middle Jurassic atoposaurid (Crocodylomorpha, Neosuchia), and a discussion on the genus Theriosuchus
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 to Theriosuchus based on several derived characters, and differs from the five previously recognized species within this genus. Despite several diagnostic features, we conservatively refer it to Theriosuchus sp., 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 of Theriosuchus, 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.
Atoposauridae, Bathonian, Crocodyliformes, Scotland, Valtos Sandstone Formation
0024-4082
443-462
Young, Mark T.
d9880973-1dd1-4b1c-81a8-7494170dbac2
Tennant, Jonathan P.
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Brusatte, Stephen L.
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Challands, Thomas J.
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Fraser, Nicholas C.
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Clark, Neil D.L.
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Ross, Dugald A.
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Young, Mark T.
d9880973-1dd1-4b1c-81a8-7494170dbac2
Tennant, Jonathan P.
9b0914cd-101d-48a7-9f6c-c9629e8a0781
Brusatte, Stephen L.
80497252-b249-4d92-a0a0-9975734d97af
Challands, Thomas J.
f0f73e72-9645-4b23-a2ff-0a83469b3308
Fraser, Nicholas C.
997a42fe-7bbb-44d0-86b1-66be1634702f
Clark, Neil D.L.
d5940e5d-aefb-4789-8064-31f4c811e0e5
Ross, Dugald A.
716f4c25-5612-4094-b706-41d5077956c5

Young, Mark T., Tennant, Jonathan P., Brusatte, Stephen L., Challands, Thomas J., Fraser, Nicholas C., Clark, Neil D.L. and Ross, Dugald A. (2016) The first definitive Middle Jurassic atoposaurid (Crocodylomorpha, Neosuchia), and a discussion on the genus Theriosuchus. Zoological Journal of the Linnean Society, 176 (2), 443-462. (doi:10.1111/zoj.12315).

Record type: Article

Abstract

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 to Theriosuchus based on several derived characters, and differs from the five previously recognized species within this genus. Despite several diagnostic features, we conservatively refer it to Theriosuchus sp., 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 of Theriosuchus, 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.

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Accepted/In Press date: 24 June 2015
e-pub ahead of print date: 9 September 2015
Published date: February 2016
Keywords: Atoposauridae, Bathonian, Crocodyliformes, Scotland, Valtos Sandstone Formation
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 381669
URI: http://eprints.soton.ac.uk/id/eprint/381669
ISSN: 0024-4082
PURE UUID: 2ef0d065-a3ea-43e9-8d3b-0977da10480b

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Date deposited: 17 Sep 2015 08:42
Last modified: 09 Jan 2022 09:49

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Contributors

Author: Mark T. Young
Author: Jonathan P. Tennant
Author: Stephen L. Brusatte
Author: Thomas J. Challands
Author: Nicholas C. Fraser
Author: Neil D.L. Clark
Author: Dugald A. Ross

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