page_title: Elasmosaurus
section_title: Formerly assigned species
hierarchical_section_title: Elasmosaurus / Formerly assigned species
caption_attribution_description: Mauisaurus Haastii. n. sp. Transactions and Proceedings of the Royal Society of New Zealand Volume 6, 1873
context_page_description: 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.
  Measuring 10.3 meters long, Elasmosaurus would have had a streamlined body with paddle-like limbs, a short tail, a small head, and an extremely long neck. The neck alone was around 7.1 meters long.
context_section_description: Following the description of the type species, E. platyurus, a number of other Elasmosaurus species were described by Cope, Williston, and other authors. However, none of these species are still definitely referable to the genus Elasmosaurus today, and most of them either have been moved to genera of their own or are considered dubious names, nomina dubia – that is, with no distinguishing features, and therefore of questionable validity.
  Accompanying his 1869 description of E. platyurus, Cope named another species of Elasmosaurus, E. orientalis, based on two dorsal vertebrae from New Jersey. He distinguished E. orientalis from E. platyurus by the more strongly developed processes known as parapophyses on the vertebrae, in which he considered it to approach closer to Cimoliasaurus; however, he still assigned it to Elasmosaurus on account of its large size and angled sides. The first of these vertebrae was used as a doorstop in a tailor's shop, whereas the other was found in a pit by Samuel Lockwood, a superintendent. Cope gave the name orientalis to the new species, on account of it possibly having a more easterly distribution than E. platyurus. Leidy subsequently moved E. orientalis to the now dubious genus Discosaurus in the following year. In 1952 Welles considered the species a nomen dubium, given how fragmentary it was.
  In 1869 Cope also published an article about the fossil reptiles of New Jersey, wherein he described E. orientalis as an animal with a "long neck". Yet, in an accompanying illustration Cope showed a short-necked Elasmosaurus confronting a Dryptosaurus (then Laelaps), with a plesiosaur-like Mosasaurus and other animals in the background. According to Davidson, it is uncertain which species of Elasmosaurus is depicted, but if it is E. orientalis, the short neck contradicts Cope's own text, and if E. platyurus, he showed the animal with a short neck after acknowledging this was incorrect. Davidson has suggested that even though Leidy had pointed out Cope's error in 1868, Cope may not have accepted this. In an 1870 reply to Leidy, Cope himself stated that the generic placement of E. orientalis was in doubt, and that he had illustrated it with a short neck due to believing this was the condition of Cimoliasaurus. If more remains showed E. orientalis to have had a long neck like Elasmosaurus, he stated the image may instead represent Cimoliasaurus better.
  In the same 1869 publication wherein he named E. platyurus and E. orientalis, Cope assigned an additional species, E. constrictus, based on a partial centrum from a neck vertebra found in the Turonian-aged clay deposits at Steyning, Sussex, in the United Kingdom. It was described by the British paleontologist Richard Owen as Plesiosaurus constrictus in 1850; Owen named the species after the extremely narrow breadth of the vertebra between the pleurapophyses, or the processes that articulate between the ribs. He considered this to be partially an artifact of preservation, but could not understand how the compression affected only the central portion and not the articular ends of the centrum. Cope recognized this as a natural condition, and considered constrictus to be "a species of Elasmosaurus or an ally". In 1962 Welles considered P. constrictus to be a nomen dubium, given its fragmentary nature. Per Ove Persson retained it as valid in 1963, noting the longitudinal ridge on the sides of the centra as an elasmosaurid trait. In 1995 Nathalie Bardet and Pascal Godefroit also recognized it as an elasmosaurid, albeit indeterminate.
  Cope discovered another elasmosaurid skeleton in 1876. He named it as a new species, E. serpentinus, in 1877, and differentiated it by the lack of compression in the rear neck vertebrae, the presence of few sessile ribs among the first few dorsals, and the presence of "weak angles" below the front tail vertebrae. Cope had also discovered another large skeleton that bore great resemblance to the known remains of E. orientalis from the black shale of the "Cretaceous bed No. 4"; he excavated it with the help of George B. Cledenning and
caption: Remains of E. haasti (now Mauisaurus haasti)
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