Charles de Gerville and the first remains of Plesiosauria reported in the Lower Jurassic of France (Hettangian, Valognes region, Manche department)

The historian, archaeologist, and naturalist Charles de Gerville (1769–1853) reported as early as January 1816 the presence of fossil bones in the quarries of the region of Valognes, in the department of Manche. These quarries exploited the “Calcaire de Valognes” and the underlying “Argiles et Calcaires d’Huberville”, both formations dated as Lower Hettangian (Lower Jurassic). De Gerville communicated to Jacques-Louis-Marin Defrance a watercolour drawing of one of these fossil bones, discovered in July 1820, in which it is possible to recognize a plesiosaur femur. This femur, as well as a fragment of rib and three vertebrae of Plesiosauria from de Gerville's collection, was then figured in a publication by Arcisse de Caumont, in 1825. The plesiosaur femur was later acquired by Pierre Tesson of Caen, who owned one of the most important collections of fossils in Normandy. The Tesson collection was later purchased in 1857 by the British Museum (now The Natural History Museum, London), where the femur has been rediscovered. This specimen is the first known plesiosaur specimen ever discovered in the Lower Jurassic of France, before the genus Plesiosaurus was established upon material from the Lias of southwestern England. One of the vertebrae figured by de Caumont has been rediscovered in the “Muséum Emmanuel-Liais” (Cherbourg-en-Cotentin), which had acquired part of de Gerville's collection. The interpretation of the “fossil bones of Valognes” by Georges Cuvier, Henri Marie Ducrotay de Blainville, Arcisse de Caumont, Jacques-Amand Eudes-Deslongchamps and Constant Duméril is revealed through unpublished documents.