Genus author:
Welles, 1943
Maastrichtian, Late Cretaceous
Panoche hills, south of Moreno Gulch, near Mendota, Fresno County, California, USA
Referred material (sp.):
Type species:

H. alexandrae

H. alexandrae
Species author:
Welles, 1943
Type specimen:
U. C. Mus. Pal. no 33912. A nearly complete skeleton.
Maastrichtian, Late Cretaceous
Geological formation:
Type location:
Sun Ray gypsum mine in the Panoche hills, south of Moreno Gulch, near Mendota, Freso County, California, USA
Referred material:

Hydrotherosaurus is a long-necked elasmosaurid from California, USA. It is represented by one of the most complete elasmosaurid skeletons ever discovered, so Hydrotherosaurus is one of the best known members of this family. The almost complete type skeleton of Hydrotherosaurus was discovered in the Panoche Hills by Mr. Frank C. Paiva in 1937, and was excavated by the University of California Museum of Palaeontology, Berkeley, and Fresno State College. A cast of the holotype skeleton is on public display in the California Academy of Sciences.

The taxon was named and described in detail by Samuel P. Welles (1943, 1952) and differs most obviously from other elasmosaurids in its cervical vertebral count of 60. Welles (1943) derived the genus name from the word “fisherman”, hence “fisherman lizard”. However, the genus translates more literally as “water beast reptile”.

Skull of Hydrotherosaurus in dorsal and lateral view, from Welles (1943).
Skull of Hydrotherosaurus
Skeleton of Hydrotherosaurus in lateral view, from Welles (1943).
Articulated skeleton of Hydrotherosaurus. From Welles 1943.
Hydrotherosaurus head painting by Zdenek Burian.
Hydrotherosaurus by CollectA (formerly Procon)