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.
Umoonasaurus is an extinct genus of plesiosaur belonging to the family Leptocleididae. This genus lived approximately 115 million years ago during the Early Cretaceous period, in shallow seas covering parts of what is now Australia. It was a relatively small animal around 2.5 metres (8.2 ft) long. An identifying trait of Umoonasaurus is three crest-ridges on its skull.
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.
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.
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.
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.
Nichollssaura is an extinct genus of leptocleidid plesiosaur from the Early Cretaceous Boreal Sea of North America. The type species is N. borealis, found in the early Albian age Clearwater Formation near Fort McMurray, Alberta, Canada.
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. quiriquinensis, 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.
Brancasaurus is a genus of plesiosaur which lived in a freshwater lake in the Early Cretaceous of what is now North Rhine-Westphalia, Germany. With a long neck possessing vertebrae bearing distinctively-shaped "shark fin"-shaped neural spines, and a relatively small and pointed head, Brancasaurus is superficially similar to Elasmosaurus, albeit smaller in size at 3.26 metres (10.7 ft) in length as a subadult.
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).
The Clearwater Formation is a stratigraphic unit of Early Cretaceous (Albian) age in the Western Canada Sedimentary Basin in northeastern Alberta, Canada. It was first defined by R.G. McConnell in 1893 and takes its name from the Clearwater River near Fort McMurray.
Athabascasaurus is an extinct genus of platypterygiine ophthalmosaurid ichthyosaur known from Alberta, Canada.
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.
Nakonanectes bradti is an elasmosaurid plesiosaur of the late Cretaceous found in 2010 the state of Montana in the United States. It is one of the most recently known elasmosaurids to have lived in North America. Unlike other elasmosaurids, it has a relatively short neck.
