Plesiosauroidea is an extinct clade of carnivorous marine reptiles. They have the snake-like longest neck to body ratio of any reptile. Plesiosauroids are known from the Jurassic and Cretaceous periods. After their discovery, some plesiosauroids were said to have resembled "a snake threaded through the shell of a turtle", although they had no shell.
Elasmosaurus is a genus of plesiosaur that lived in North America during the Campanian stage of the Late Cretaceous period, about 80.5 million years ago. The first specimen was discovered in 1867 near Fort Wallace, Kansas, US, and was sent to the American paleontologist Edward Drinker Cope, who named it E. platyurus in 1868. The generic name means "thin-plate reptile", and the specific name means "flat-tailed". Cope originally reconstructed the skeleton of Elasmosaurus with the skull at the end of the tail, an error which was made light of by the paleontologist Othniel Charles Marsh, and became part of their "Bone Wars" rivalry. Only one incomplete Elasmosaurus skeleton is definitely known, consisting of a fragmentary skull, the spine, and the pectoral and pelvic girdles, and a single species is recognized today; other species are now considered invalid or have been moved to other genera.
Elasmosauridae is an extinct family of plesiosaurs, often called elasmosaurs. They had the longest necks of the plesiosaurs and existed from the Hauterivian to the Maastrichtian stages of the Cretaceous, and represented one of the two groups of plesiosaurs present at the end of the Cretaceous alongside Polycotylidae.
Polycotylidae is a family of plesiosaurs from the Cretaceous, a sister group to Leptocleididae. They are known as false pliosaurs. 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 early Maastrichtian around 72 million years ago. The possible latest surviving member Rarosaurus from the late Maastrichtian is more likely a crocodylomorph.
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 prehistoric marine reptile measuring around 3 metres (9.8 ft) long. Its Greek generic name means "long-nosed face".
Edgarosaurus is a genus of polycotylid plesiosaur from the Thermopolis Shale, containing one species, E. muddi. The type specimen was found in Early Cretaceous 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.
Brachauchenius is an extinct genus of pliosaurid that lived in North America and Morocco during the Late Cretaceous.
The Bearpaw Formation, also called the Bearpaw Shale, is a geologic formation of Late Cretaceous (Campanian) age. It outcrops in the U.S. state of Montana, as well as the Canadian provinces of Alberta and Saskatchewan, and was named for the Bear Paw Mountains in Montana. It includes a wide range of marine fossils, as well as the remains of a few dinosaurs. It is known for its fossil ammonites, some of which are mined in Alberta to produce the organic gemstone ammolite.
Aphrosaurus was an extinct genus of plesiosaur from the Maastrichtian. The type species is Aphrosaurus furlongi, named by Welles in 1943. The holotype specimen was discovered in the Moreno Formation in Fresno County, California in 1939 by rancher Frank C. Piava. A second specimen - LACM 2832 - was also found in the same formation and initially diagnosed as a juvenile of the same species, but has since been removed from the genus.
Styxosaurus is a genus of plesiosaur of the family Elasmosauridae. Styxosaurus lived during the Campanian age of the Cretaceous period. Three species are known: S. snowii, S. browni, and S. rezaci.
The Pierre Shale is a geologic formation or series in the Upper Cretaceous which occurs east of the Rocky Mountains in the Great Plains, from Pembina Valley in Canada to New Mexico.
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.
This timeline of plesiosaur research is a chronologically ordered list of important fossil discoveries, controversies of interpretation, taxonomic revisions, and cultural portrayals of plesiosaurs, an order of marine reptiles that flourished during the Mesozoic Era. The first scientifically documented plesiosaur fossils were discovered during the early 19th century by Mary Anning. Plesiosaurs were actually discovered and described before dinosaurs. They were also among the first animals to be featured in artistic reconstructions of the ancient world, and therefore among the earliest prehistoric creatures to attract the attention of the lay public. Plesiosaurs were originally thought to be a kind of primitive transitional form between marine life and terrestrial reptiles. However, now plesiosaurs are recognized as highly derived marine reptiles descended from terrestrial ancestors.
Megacephalosaurus is an extinct genus of short-necked pliosaur that inhabited the Western Interior Seaway of North America about 94 to 93 million years ago during the Turonian stage of the Late Cretaceous, containing the single species M. eulerti. It is named after its large head, which is the largest of any plesiosaur in the continent and measures up to 1.75 meters (5.7 ft) in length. Megacephalosaurus was one of the largest marine reptiles of its time with an estimated length of 6–9 meters (20–30 ft). Its long snout and consistently sized teeth suggest that it preferred a diet of smaller-sized prey.
Mauriciosaurus is a genus of polycotylid plesiosaur from the Late Cretaceous of Mexico. It contains a single species, M. fernandezi, described in 2017 by Eberhard Frey and colleagues from a single well-preserved juvenile specimen about 1.9 metres 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 ridges on the bottom of the parasphenoid bone on its palate; the narrow openings in the palate bordered by the pterygoid bones; the lack of perforations in the surface of the coracoid; and the highly unusual arrangement of gastralia, or belly ribs, which is only otherwise seen in the non-polycotylid Cryptoclidus.
Luskhan is an extinct genus of brachauchenine pliosaur from the Cretaceous of Russia. The type and only species is Luskhan itilensis, named by Valentin Fischer and colleagues in 2017 from a well-preserved and nearly complete skeleton. As an early-diverging brachauchenine, Luskhan consequently exhibits an intermediate combination of traits seen in more basal and more derived pliosaurs. However, Luskhan departs significantly from other pliosaurs in that it exhibits a lack of adaptations in its skull to feeding on large prey; its slender snout, small teeth, and short tooth rows instead indicate a skull adapted for feeding on small, soft prey. With these features, it is the pliosaur that approaches closest to the distantly-related piscivorous polycotylids, having convergently evolved these traits more than 10 million years apart.
Serpentisuchops 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.
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. specta, known from two partial skeletons. Unktaheela represents the smallest known polycotylid.
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.
