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. [1] Plesiosaurs were actually discovered and described before dinosaurs. [2] 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. [3] 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. [4]
Early researchers thought that plesiosaurs laid eggs like most reptiles. They commonly imagined plesiosaurs crawling up beaches and burying eggs like turtles. However, later opinion shifted towards the idea that plesiosaurs gave live birth and never went on dry land. [5] Plesiosaur locomotion has been a source of continuous controversy among paleontologists. [6] The earliest speculations on the subject during the 19th century saw plesiosaur swimming as analogous to the paddling of modern sea turtles. During the 1920s opinion shifted to the idea that plesiosaurs swam with a rowing motion. [7] However, a paper published in 1975 that once more found support for sea turtle-like swimming in plesiosaurs. [8] This conclusion reignited the controversy regarding plesiosaur locomotion through the late 20th century. [9] In 2011, F. Robin O'Keefe and Luis M. Chiappe concluded the debate on plesiosaur reproduction, reporting the discovery of a gravid female plesiosaur with a single large embryo preserved inside her. [10]
Associated remains of plesiosaurs and animals like the diving bird Hesperornis or the pterosaur Pteranodon may have inspired legends about conflict between Thunder Birds and Water Monsters told by the Native Americans of Kansas and Nebraska. [11]
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c. 1935
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In his remarks on short-necked plesiosaur evolution, Carpenter argued that polycotylids were more closely related to long-necked plesiosaurs than pliosaurs. [90] He observed that Trinacromerum bentonianum seems to have existed from the late Cenomanian to the Turonian. This represents a span of time approximating 3.3 million years. He found Dolichorhynchops osborni to have had an even longer lifespan, from the middle Turonian to the early Campanian., or roughly 4 million years. His research also suggested that there was a span of time during the life of the Western Interior Seaway in which it was not inhabited by polycotylids. [29]
He also reported that the Dolichorhynchops specimen KUVP 40001 from the Pierre Shale of South Dakota may have achieved the extraordinary length of 23 feet. [34] The large size of the Pierre Shale Dolichorhynchops compared to those of the earlier Smoky Hill Chalk suggested to Carpenter that these plesiosaurs were evolving larger body sizes over time. In fact the Pierre Shale specimens of Dolichorhynchops were nearly as large as Brachauchenius lucasi. [78] Carpenter described a particularly large specimen of that latter taxon in this paper as well, specifically FHSM VP-321. [52] His study of Brachauchenius led him to concur with Williston that it was closely related to Liopleurodon ferox. [52]
November
They also noted that some of NJSM 15435's gastroliths were scarred by rounded chips and arc-shaped marks. These were likely inflicted by contact with other gastroliths during the churning of the animal's stomach, and constituted physical evidence that plesiosaurs used their gastroliths to help break down their food during digestion. [97] Cicimurri and Everhart disputed the hypothesis that plesiosaurs used their gastroliths for ballast on the grounds that swallowing and vomiting such stones would be relatively difficult for the long-necked forms and their feeding grounds may have been hundreds of miles from sources of stones. [98]
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September 11
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2001– 2002
December 30
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.
The Plesiosauria or Plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia.
Thalassomedon is a genus of plesiosaur, named by Welles in 1943.
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.
Libonectes is an extinct genus of sauropterygian reptile belonging to the plesiosaur order. It is known from specimens found in the Britton Formation of Texas (USA) and the Akrabou Formation of Morocco, which have been dated to the lower Turonian stage of the late Cretaceous period.
Dolichorhynchops is an extinct genus of polycotylid plesiosaur from the Late Cretaceous of North America, containing three species, D. osborni, D. bonneri and D. tropicensis, as well as a questionably referred fourth species, D. herschelensis. Dolichorhynchops was a prehistoric marine reptile, but at least one species, D. tropicensis, likely entered rivers to collect gastroliths. Its Greek generic name means "long-nosed face". While typically measuring about 3 metres (9.8 ft) in length, the largest specimens of D. osborni and D. bonneri are estimated to have a total body length more than approximately 4.29 metres (14.1 ft) and 5.09 metres (16.7 ft), respectively.
Brachauchenius is an extinct genus of pliosaurid that lived in North America and Morocco during the Late Cretaceous.
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.
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.
Aristonectes is an extinct genus of large elasmosaurid plesiosaurs that lived during the Maastrichtian stage of the Late Cretaceous. It is the type genus of the subfamily Aristonectinae, a lineage of elasmosaurids characterized by an enlarged skull and a reduced length of the neck. Two species are known, A. parvidens and A. quiriquensis, whose fossil remains were discovered in what are now Patagonia an Antarctica. Throughout the 20th century, Aristonectes was a rather difficult animal for scientists to analyze due to poor fossil preparation, and was sometimes declared as an uncertain taxon. Subsequent revisions and discoveries carried out from the beginning of the 21st century have re-established the genus as valid.
Morenosaurus is an extinct genus of plesiosaur from the Cretaceous of what is now California. The type species is Morenosaurus stocki, first named by Samuel Welles in 1943, in honor of Dr. Chester Stock. The species was found by Robert Wallace and Arthur Drescher in the Panoche Hills region of Fresno County. The skeleton they found was fairly complete, and lacked only the head and parts of the neck and paddles; the preserved portion of the trunk and tail is 3.63 metres (11.9 ft) long. The skeleton was originally mounted at Caltech but is now in the Natural History Museum of Los Angeles County.
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.
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.
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.
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.
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