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. Their diet mainly consisted of crustaceans and molluscs.
Muraenosaurus is an extinct genus of cryptoclidid plesiosaur reptile from the Oxford Clay of Southern England. The genus was given its name due to the eel-like appearance of the long neck and small head. Muraenosaurus grew up to 5.2 metres (17 ft) in length and lived roughly between 160 Ma and 164 Ma in the Callovian of the middle Jurassic. Charles E. Leeds collected the first Muraenosaurus which was then described by H. G. Seeley. The specimen may have suffered some damage due to the casual style of Charles Leeds’ collection. The first muraenosaur was recovered with pieces missing from the skull and many of the caudal vertebrae absent. Because the animal was described from Charles Leeds’ collection it was given the name Muraenosaurus Leedsi. M. leedsi is the most complete specimen belonging to the genus Muraenosaurus and also the only species that is undoubtedly a member of the genus. Two other species have been tentatively referred to as members of the genus Muraenosaurus: M. reedii and Muraenosaurus beloclis Seeley 1892, which in 1909 became the separate genus Picrocleidus.
Mauisaurus is a dubious genus of plesiosaur that lived during the Late Cretaceous period in what is now New Zealand. Numerous specimens have been attributed to this genus in the past, but a 2017 paper restricts Mauisaurus to the lectotype and declares it a nomen dubium.
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.
Tuarangisaurus is an extinct genus of elasmosaurid known from New Zealand. The type and only known species is Tuarangisaurus keyesi, named by Wiffen and Moisley in 1986.
Terminonatator is a genus of elasmosaurid plesiosaur from the Late Cretaceous of Saskatchewan, Canada. It is known from a skull and partial skeleton from a young adult, found in the Campanian-age Bearpaw Formation near Notukeu Creek in Ponteix. Terminonatator is currently one of the youngest plesiosaurs from the Western Interior Seaway.
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.
Callawayasaurus is a genus of plesiosaur from the family Elasmosauridae. When the holotype was first described by Samuel Paul Welles in 1962, it was described as Alzadasaurus colombiensis before being moved into its current genus by Kenneth Carpenter in 1999.
Aristonectes is an extinct genus of large elasmosaurid plesiosaurs that lived during the Maastrichtian stage of the Late Cretaceous. Two species are known, A. parvidens and A. quiriquensis, whose fossil remains were discovered in what are now Patagonia and Antarctica. Throughout the 20th century, Aristonectes was a difficult animal for scientists to analyze due to poor fossil preparation, its relationships to other genera were uncertain. After subsequent revisions and discoveries carried out from the beginning of the 21st century, Aristonectes is now recognised as the type genus of the subfamily Aristonectinae, a lineage of elasmosaurids characterized by an enlarged skull and a reduced length of the neck.
Eromangasaurus is an extinct genus of elasmosaurid known from northern Queensland of Australia.
Tatenectes is a genus of cryptoclidid plesiosaur known from the Upper Jurassic of Wyoming. Its remains were recovered from the Redwater Shale Member of the Sundance Formation, and initially described as a new species of Cimoliosaurus by Wilbur Clinton Knight in 1900. It was reassigned to Tricleidus by Maurice G. Mehl in 1912 before being given its own genus by O'Keefe and Wahl in 2003. Tatenectes laramiensis is the type and only species of Tatenectes. While the original specimen was lost, subsequent discoveries have revealed that Tatenectes was a very unusual plesiosaur. Its torso had a flattened, boxy cross-section and its gastralia exhibit pachyostosis (thickening). The total length of Tatenectes has been estimated at 2–3 meters (6.6–9.8 ft).
Stratesaurus is an extinct genus of small-bodied rhomaleosaurid plesiosaur known from the Early Jurassic period of the United Kingdom. It contains a single species, S. taylori. It was a small plesiosaur, with a skull length of 18 cm (7.1 in) and a body length of 2 m (6.6 ft).
Albertonectes is an extinct genus of elasmosaurid plesiosaur known from the Late Cretaceous Bearpaw Formation of Alberta, Canada. It contains a single species, Albertonectes vanderveldei. Albertonectes is the longest elasmosaur, and more generally plesiosaur, known to date both in neck and total body length.
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.
Cardiocorax is an extinct genus of elasmosaurid known from the Late Cretaceous Mocuio Formation of Namibe Province, southern Angola. It contains a single species, Cardiocorax mukulu.
Kawanectes is a genus of elasmosaurid plesiosaur, a type of long-necked marine reptile, that lived in the marginal marine environment of Late Cretaceous Patagonia. It contains one species, K. lafquenianum, described in 2016 by O'Gorman.
Lagenanectes is a genus of elasmosaurid plesiosaur from the Lower Cretaceous, found in Lower Saxony, Germany. The only species, Lagenanectes richterae, was first described in 2017, and is regarded as one of the best-preserved plesiosaur fossils from this geological age in Europe. Lagenanectes is one of the earliest elasmosaurids. The holotype is an incomplete skeleton, comprising large parts of the skull, some neck and tail vertebrae as well as ribs and part of the limbs. A length of about 8 meters has been estimated.
Plesioelasmosaurus is an extinct genus of elasmosaurid plesiosaur from the Late Cretaceous Greenhorn Limestone of Kansas, United States. The genus contains a single species, P. walkeri, known from a partial skeleton.
