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1 September 2014 Anatomy of Colymbosaurus megadeirus (Reptilia, Plesiosauria) from the Kimmeridge Clay Formation of the U.K., and High Diversity Among Late Jurassic Plesiosauroids
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Abstract

We describe the syntype postcranial skeletons of the cryptoclidid plesiosauroid Colymbosaurus megadeirus. C. megadeirus is the type species of Colymbosaurus, and one other valid species, C. svalbardensis, is known. Although it is in widespread usage, C. trochanterius is a not valid species, although the presence of an anteroposteriorly oriented ridge bisecting the distal surfaces of the holotype humerus allows its referral to Colymbosaurus sp. Some specimens previously referred to C. trochanterius, including the holotype of ‘Plesiosaurus’ manselii, lack this feature, or show other differences from our hypodigm, suggesting that they are taxonomically distinct from Colymbosaurus, and countering previous suggestions that the Kimmeridge Clay Formation represents a depauperate plesiosauroid fauna. Substantial differences between the atlas-axis complexes and cervical vertebrae of Kimmerosaurus langhami, ‘Plesiosaurus’ manselii, C. megadeirus, and specimens referred here to cf. Spitrasaurus indicate that at least four plesiosauroid taxa were present in the Kimmeridge Clay Formation. This proposition is also supported by coracoid morphotypes, and demonstrates that Late Jurassic plesiosauroids were taxonomically diverse. Most Late Jurassic-Early Cretaceous cryptoclidids belong to a monophyletic Colymbosaurinae, but Kimmerosaurus and its sister taxon Tatenectes originated independently from Middle Jurassic cryptoclidids.

© 2014 by the Society of Vertebrate Paleontology
Roger B. J. Benson and Timothy Bowdler "Anatomy of Colymbosaurus megadeirus (Reptilia, Plesiosauria) from the Kimmeridge Clay Formation of the U.K., and High Diversity Among Late Jurassic Plesiosauroids," Journal of Vertebrate Paleontology 34(5), (1 September 2014). https://doi.org/10.1080/02724634.2014.850087
Received: 19 July 2013; Accepted: 1 September 2013; Published: 1 September 2014
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