Polycotylidae

Trinacromerum is an extinct genus of sauropterygian reptile, a member of the polycotylid plesiosaurs. It contains two species, T. bentonianum and T. kirki. Specimens have been discovered in the Late Cretaceous fossil deposits of what is now modern Kansas and Manitoba. Some fossils are also found in the Southern United States such as in the Mooreville Chalk of Alabama.

Dolichorhynchops is an extinct genus of polycotylid plesiosaur from the Late Cretaceous of North America, containing the species D. osborni and D. herschelensis, with two previous species having been assigned to new genera. Definitive specimens of D. osborni have been found in the late Coniacian to early Campanian rocks, while those of D. herschelensis have been found in the late Campanian to early Maastrichtian rocks. Dolichorhynchops was a relatively small plesiosaur, measuring around long. Its Greek generic name means "long-nosed face".

Plesiopleurodon (/ˌpliːsiəˈplʊərədɒn/; , meaning "near to", pleuro, meaning "side", and don, meaning "tooth") is an extinct genus of Mesozoic marine reptiles, belonging to the Sauropterygia, known from the Late Cretaceous of North America. It was named by Kenneth Carpenter based on a complete skull with a mandible, cervical vertebra, and a coracoid. In naming the specimen, Carpenter noted "Of all known pliosauroids, Plesiopleurodon wellesi most closely resembles Liopleurodon ferox from the Oxfordian of Europe, hence the generic reference." It was initially described as a pliosauroid due to it

Polycotylidae is a family of plesiosaurs from the Cretaceous. Polycotylids first appeared during the Albian stage of the Early Cretaceous, before becoming abundant and widespread during the early Late Cretaceous. Several species survived into the final stage of the Cretaceous, the Maastrichtian around . The possible latest surviving member Rarosaurus from the late Maastrichtian is more likely a crocodylomorph.

Edgarosaurus is a genus of polycotylid plesiosaur from the Thermopolis Shale, containing one species, E. muddi. The type specimen was found in Early Cretaceous (late Albian) rocks in the state of Montana in the United States. At the time, this location was covered by part of the Western Interior Seaway. Edgarosaurus was one of the first polycotylids that evolved to become native to the Western Interior Seaway.

Sulcusuchus is a genus of polycotylid plesiosaur from the Maastrichtian of Argentina.

Thililua is a genus of polycotylid plesiosaur, containing one species, T. longicollis.

Polycotylus is a genus of plesiosaur within the family Polycotylidae. The type species is P. latippinis and was named by American paleontologist Edward Drinker Cope in 1869. Eleven other species have been identified. The name means 'much-cupped vertebrae', referring to the shape of the vertebrae. It lived in the Western Interior Seaway of North America toward the end of the Cretaceous. One fossil preserves an adult with a single large fetus inside of it, indicating that Polycotylus gave live birth, an unusual adaptation among reptiles. ==History==

thumb|left|Skull thumb|left|Life restoration Manemergus is a genus of polycotylid plesiosaur from the Late Cretaceous (Turonian) of Morocco. Manemergus was described in 2005 and contains only one species, M. anguirostris. The type specimen was discovered close to the town of Goulmima (Tizi-n-Imnayen) in Morocco's High Atlas mountains, in the same locality as another polycotylid, Thililua, was discovered.

Eopolycotylus is a genus of polycotylid plesiosaur known from the Cenomanian-age Tropic Shale of Utah.

Palmulasaurus is a genus of polycotylid plesiosaur from the Turonian Tropic Shale of Utah. It was originally described as Palmula, but that name was already occupied by a genus of Cretaceous foraminifera first described in 1833.

Serpentisuchops (meaning "snaky crocodile-face") is a genus of polycotylid plesiosaur from the late Cretaceous Pierre Shale of Wyoming, United States. The genus contains a single species, S. pfisterae, known from a partial skeleton.

Pahasapasaurus is an extinct genus of polycotylid plesiosaurs from Late Cretaceous rocks of the United States. Distinctive features of the taxon include elongate epipodial bones (radius/ulna - tibia/fibula) and the nature of the palate bones (roof of the mouth). The genus contains two species; type species, Pahasapasaurus haasi, was named in 2007 based on remains from the late Cenomanian-aged Greenhorn Limestone of South Dakota, In 2025, a second species was named, Pahasapasaurus gillettei, based on a complete skull and partial skeleton from the early Turonian-aged Tropic Shale of Utah.

Mauriciosaurus (meaning "Mauricio [Fernández Garza's] reptile") is a genus of polycotylid plesiosaur from the Late Cretaceous of Mexico. It contains a single species, M. fernandezi (also named after Fernández Garza), described in 2017 by Eberhard Frey and colleagues from a single well-preserved juvenile specimen about long. Morphologically, it is overall most similar to the polycotyline polycotylids Trinacromerum and Dolichorhynchops. However, several features separate Mauriciosaurus from all other polycotylids, warranting the naming of a new genus. These include the sophisticated pattern of r

Georgiasaurus ("Georgy's lizard"; after V. A. Otschev's father, Georgy Otschev, a geodesist who died shortly before Otschev published the description in 1976) is an extinct genus of plesiosaur from the Late Cretaceous of Russia. Otschev (or Ochev) originally named the specimen Georgia, but that name was preoccupied by the colubrid snake Georgia Baird & Girard, 1853. Originally a complete skeleton, the specimen, holotype POKM 11658 consisting of seven neck vertebrae, vertebral impressions, both scapulae and two limbs, was damaged in preparation of the quarry stone. It was found near the village

Martinectes is an extinct genus of polycotylid plesiosaur from the Late Cretaceous (Campanian stage) of North America and possibly European Russia. The genus contains a single species M. bonneri, known from multiple skeletons and skulls. Martinectes was historically considered to represent a species of the genus Trinacromerum and later Dolichorhynchops before it was moved to its own genus. It was a large polycotylid measuring around long.

Scalamagnus is an extinct genus of polycotylid plesiosaur from the Late Cretaceous Tropic Shale Formation of the United States. The genus contains a single species S. tropicensis, known from a skull and two partial skeletons. Scalamagnus was historically considered to represent a species of the genus Dolichorhynchops before it was moved to its own genus.

Unktaheela is an extinct genus of polycotylid plesiosaur from the Late Cretaceous Sharon Springs Formation of the United States. The genus contains a single species, U. , known from two skulls and partial skeletons. Unktaheela represents the smallest known polycotylid.