Seeleyosaurus Temporal range: Early Jurassic, Toarcian PreꞒ Ꞓ O S D C P T J K Pg N
Cast of Seeleyosaurus guilelmiimperatoris fossil with reconstructed parts based on the holotype
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	†Sauropterygia
Order:	†Plesiosauria
Family:	†Microcleididae
Genus:	†Seeleyosaurus White, 1940
Type species
†Seeleyosaurus guilelmiimperatoris (Dames, 1895)
Synonyms
Plesiosaurus guilelmiimperatoris Dames, 1895 Seeleyosaurus holzmadensis White, 1940

Seeleyosaurus is an extinct genus of plesiosaur that was initially placed within the genus Plesiosaurus in 1895^[1] and was given its own genus in 1940.^[2] Two species were known: the type, S. guilelmiimperatoris, and the now obsolete species S. holzmadensis,^[2] which has since been absorbed into S. guilelmiimperatoris. It was a relatively small plesiosaur, measuring 2.9–3.6 m (9.5–11.8 ft) long.^[3][4] The holotype is MB.R.1992, a large almost complete skeleton from the Upper Lias (Toarcian) Lias Group Formations of Württemberg, Germany. There seems to be the impression of a rhomboidal flap of skin in a vertical plane; if so, many plesiosaurs may have been equipped in this way.^[5] A second specimen (SMNS 12039), preserved in 3D, is the holotype of S. holzmadensis.^[2]

Classification

The following cladogram follows an analysis by Ketchum & Benson, 2011.^[5]

Gallery

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  Restoration
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  Holotype of S. guilelmiimperatoris in 1895^[1]
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  Seeleyosaurus (left) and Thaumatosaurus, now Meyerasaurus (right) as depicted in Water reptiles of the past and present (1914)