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A new leptocleidid (Sauropterygia, Plesiosauria) from the Vectis Formation (Early Barremian–early Aptian; Early Cretaceous) of the Isle of Wight and the evolution of Leptocleididae, a controversial clade

A new leptocleidid (Sauropterygia, Plesiosauria) from the Vectis Formation (Early Barremian–early Aptian; Early Cretaceous) of the Isle of Wight and the evolution of Leptocleididae, a controversial clade
A new leptocleidid (Sauropterygia, Plesiosauria) from the Vectis Formation (Early Barremian–early Aptian; Early Cretaceous) of the Isle of Wight and the evolution of Leptocleididae, a controversial clade
Among the most enigmatic and controversial plesiosaurian clades is the Early Cretaceous Leptocleididae, a small group of (mostly) short-necked taxa with ‘intermediate' or ‘pliosauromorph' body proportions. Leptocleidids have often been interpreted as basal members of Pliosauroidea, and their presence in marginal marine and even freshwater facies has led to suggestions that they might represent late-surviving relicts, perhaps related to the Lower Jurassic rhomaleosaurids. We describe a new leptocleidid, Vectocleidus pastorum gen. et sp. nov., from the late Barremian part of the Cowleaze Chine Member (Vectis Formation), Isle of Wight, UK, and undertake a detailed reassessment of leptocleidid anatomy and relationships. New data on the long-necked Brancasaurus gives extra support to a monophyletic Leptocleididae with taxa of ‘intermediate' body plan and robust skulls, Leptocleidus superstes, Leptocleidus capensis, Nichollssaura and Vectocleidus. Thus, leptocleidids adopted a range of body plans on the pliosauromorph–plesiosauromorph spectrum. Support for a placement of Leptocleididae within Pliosauroidea is weak, and most proposed synapomorphies fail the test of similarity. However, numerous synapomorphies, including many new observations, support a derived position within Plesiosauroidea. Thus, the ‘intermediate' body plan of many leptocleidids is not plesiomorphic, and plesiosaurian body plan evolution was complex and highly plastic. We also summarize the anatomy of ‘Cimoliasaurus' valdensis, a short-necked Early Cretaceous taxon. ‘C.' valdensis is a valid taxon for which we erect the new monotypic genus Hastanectes. Hastanectes shows evidence of possible pliosaurid affinities. Thus, multiple plesiosaurian clades may have invaded margin and freshwater environments.
plesiosaurians, Leptocleidia, Wealden, body plan evolution, Early Cretaceous
1477-2019
233-250
Benson, Roger B.J.
4d625c64-d890-4995-ace0-3c71a9a1cffd
Ketchum, Hilary F.
4cb0b9ca-7529-4461-a0e4-55ffcd140ee7
Naish, Darren
6cd448f6-99cc-4c45-93d1-bdd24ee3d281
Turner, Langan E.
b196eeb8-e166-4a96-9507-e9a51e6d722f
Benson, Roger B.J.
4d625c64-d890-4995-ace0-3c71a9a1cffd
Ketchum, Hilary F.
4cb0b9ca-7529-4461-a0e4-55ffcd140ee7
Naish, Darren
6cd448f6-99cc-4c45-93d1-bdd24ee3d281
Turner, Langan E.
b196eeb8-e166-4a96-9507-e9a51e6d722f

Benson, Roger B.J., Ketchum, Hilary F., Naish, Darren and Turner, Langan E. (2013) A new leptocleidid (Sauropterygia, Plesiosauria) from the Vectis Formation (Early Barremian–early Aptian; Early Cretaceous) of the Isle of Wight and the evolution of Leptocleididae, a controversial clade. Journal of Systematic Palaeontology, 11 (2), 233-250. (doi:10.1080/14772019.2011.634444).

Record type: Article

Abstract

Among the most enigmatic and controversial plesiosaurian clades is the Early Cretaceous Leptocleididae, a small group of (mostly) short-necked taxa with ‘intermediate' or ‘pliosauromorph' body proportions. Leptocleidids have often been interpreted as basal members of Pliosauroidea, and their presence in marginal marine and even freshwater facies has led to suggestions that they might represent late-surviving relicts, perhaps related to the Lower Jurassic rhomaleosaurids. We describe a new leptocleidid, Vectocleidus pastorum gen. et sp. nov., from the late Barremian part of the Cowleaze Chine Member (Vectis Formation), Isle of Wight, UK, and undertake a detailed reassessment of leptocleidid anatomy and relationships. New data on the long-necked Brancasaurus gives extra support to a monophyletic Leptocleididae with taxa of ‘intermediate' body plan and robust skulls, Leptocleidus superstes, Leptocleidus capensis, Nichollssaura and Vectocleidus. Thus, leptocleidids adopted a range of body plans on the pliosauromorph–plesiosauromorph spectrum. Support for a placement of Leptocleididae within Pliosauroidea is weak, and most proposed synapomorphies fail the test of similarity. However, numerous synapomorphies, including many new observations, support a derived position within Plesiosauroidea. Thus, the ‘intermediate' body plan of many leptocleidids is not plesiomorphic, and plesiosaurian body plan evolution was complex and highly plastic. We also summarize the anatomy of ‘Cimoliasaurus' valdensis, a short-necked Early Cretaceous taxon. ‘C.' valdensis is a valid taxon for which we erect the new monotypic genus Hastanectes. Hastanectes shows evidence of possible pliosaurid affinities. Thus, multiple plesiosaurian clades may have invaded margin and freshwater environments.

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More information

Published date: 2013
Keywords: plesiosaurians, Leptocleidia, Wealden, body plan evolution, Early Cretaceous
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 352050
URI: http://eprints.soton.ac.uk/id/eprint/352050
ISSN: 1477-2019
PURE UUID: e9447f22-5d35-4bf8-98c0-3f4f53c72a89

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Date deposited: 30 Apr 2013 09:45
Last modified: 07 Jan 2022 21:27

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Contributors

Author: Roger B.J. Benson
Author: Hilary F. Ketchum
Author: Darren Naish
Author: Langan E. Turner

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