Editing Elasmosaurus (section)

==Formerly assigned species==
[[File:Laelaps-cope.jpg|thumb|right|alt=Inaccurate drawing of various prehistoric creatures, two of which are confronting each other in the foreground|Cope's outdated 1869 restoration of fossil reptiles from [[New Jersey]], including a short-necked ''E.{{nbsp}}orientalis'' confronting a ''[[Dryptosaurus]]'']]
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]]''{{snd}}that is, with no distinguishing features, and therefore of questionable validity.<ref name=Sachs2005/><ref name=Carpenter1999>{{cite journal |last=Carpenter |first=K. |year=1999 |title=Revision of North American elasmosaurs from the Cretaceous of the western interior |journal=Paludicola |volume=2 |issue=2 |pages=148–173|url=https://www.researchgate.net/publication/40662805}}</ref><ref name=Brown1993>{{cite journal |last=Brown |first=D. S. |year=1993 |title=A taxonomic reappraisal of the families Elasmosauridae and Cryptoclididae (Reptilia: Plesiosauroidea) |journal=Revue de Paléobiologie |volume=7 |pages=9–16}}</ref>

Accompanying his 1869 description of ''E. platyurus'', Cope named another species of ''Elasmosaurus'', ''E.{{nbsp}}orientalis'', based on two back vertebrae from New Jersey.<ref>{{cite journal|last1=Cope|first1=E. D.|title=On the reptilian orders Pythonomorpha and Streptosauria|journal=Proceedings of the Boston Society of Natural History|date=1869|volume=12|pages=265–268|url=https://www.biodiversitylibrary.org/page/9493892#page/273/mode/1up|access-date=November 12, 2017|archive-url=https://web.archive.org/web/20171112074217/https://www.biodiversitylibrary.org/page/9493892#page/273/mode/1up|archive-date=November 12, 2017|url-status=live}}</ref> He distinguished ''E.{{nbsp}}orientalis'' from ''E.{{nbsp}}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 (education)|superintendent]]. Cope gave the name ''orientalis'' to the new species, on account of it possibly having a more easterly distribution than ''E.{{nbsp}}platyurus''.<ref name="Synopsis"/> Leidy subsequently moved ''E.{{nbsp}}orientalis'' to the now dubious genus ''Discosaurus'' in the following year.<ref name="leidy1870">{{cite journal | last1 = Leidy | first1 = J. | title = April 5th | journal = Proceedings of the Academy of Natural Sciences of Philadelphia | volume = 22 | issue = 1 | date = 1870 | pages = 18–22 | jstor = 4624074 }}</ref> In 1952 Welles considered the species a ''nomen dubium'', given how fragmentary it was.<ref name="welles1952"/>

In 1869 Cope also published an article about the fossil reptiles of New Jersey, wherein he described ''E.{{nbsp}}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.{{nbsp}}orientalis'', the short neck contradicts Cope's own text, and if ''E.{{nbsp}}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.<ref name="Boneheaded"/><ref>{{cite journal|last1=Cope|first1=E. D.|title=The Fossil Reptiles of New Jersey (Continued)|journal=The American Naturalist|date=1869|volume=3|issue=2|pages=84–91|doi=10.1086/270371|jstor=2447100|doi-access=|s2cid=85021016 }}</ref> In an 1870 reply to Leidy, Cope himself stated that the generic placement of ''E.{{nbsp}}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.{{nbsp}}orientalis'' to have had a long neck like ''Elasmosaurus'', he stated the image may instead represent ''Cimoliasaurus'' better.<ref name="Additionalnote">{{cite journal | last = Cope | first = E. D. | title = Additional note on ''Elasmosaurus'' | journal = American Journal of Science | series = 2 | pages = 268–269 | url = http://oceansofkansas.com/cope1870b.html | year = 1870 | volume = 50 | access-date = November 21, 2017 | archive-url = https://web.archive.org/web/20180528074812/http://oceansofkansas.com/cope1870b.html | archive-date = May 28, 2018 | url-status = live }}</ref>

[[File:Plesiosaurus constrictus.jpg|thumb|left|alt=Drawing of a vertebra from two angles|Vertebra of ''[[Plesiosaurus]] constrictus'', which Cope assigned to ''Elasmosaurus'']]
In the same 1869 publication wherein he named ''E. platyurus'' and ''E.{{nbsp}}orientalis'', Cope assigned an additional species, ''E.{{nbsp}}constrictus'',<ref name="Synopsis"/> 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.<ref name="owen1850">{{cite book | last1 = Owen | first1 = R. | chapter = Order – Enaliosauria | title = A History of British Fossil Reptiles | volume = 1 | publisher = Cassell & Company Ltd | location = London | pages = 215–217 | chapter-url = https://books.google.com/books?id=NTJYAAAAYAAJ&pg=PA215 | date = 1850}}</ref> Cope recognized this as a natural condition, and considered ''constrictus'' to be "a species of ''Elasmosaurus'' or an ally".<ref name="Synopsis"/> In 1962 Welles considered ''P.{{nbsp}}constrictus'' to be a ''nomen dubium'', given its fragmentary nature.<ref name="welles1962">{{cite journal | last = Welles | first = S.P. | title = A new species of elasmosaur from the Aptian of Colombia and a review of the Cretaceous plesiosaurs | year = 1962 | journal = University of California Publications in Geological Sciences | volume = 44 | issue = 1 | pages = 1–96 | isbn = 978-0-598-20148-5 | oclc = 5734397 | url = http://redciencia.cu/geobiblio/paper/1962_Welles_%20rvw%20of%20K%20plesiosaurs.pdf | archive-url = https://web.archive.org/web/20220104165630/http://redciencia.cu/geobiblio/paper/1962_Welles_%20rvw%20of%20K%20plesiosaurs.pdf | archive-date = 2022-01-04}}</ref><ref name="sachsea2016">{{cite journal | last1 = Sachs | first1 = S. | last2 = Wilmsen | first2 = M. | last3 = Knüppe | first3 = J. | last4 = Hornung | first4 = J.J. | last5 = Kear | first5 = B.P. | title = Cenomanian–Turonian marine amniote remains from the Saxonian Cretaceous Basin of Germany | journal = Geological Magazine | date = 2017 | pages = 237–246 | doi = 10.1017/S0016756815001004 | volume = 154 | issue = 2| bibcode = 2017GeoM..154..237S | s2cid = 131854749 }}</ref> Per Ove Persson retained it as valid in 1963, noting the longitudinal ridge on the sides of the centra as an elasmosaurid trait.<ref name="persson1963">{{cite journal | last1 = Persson | first1 = P.O. | title = A revision of the classification of the Plesiosauria with a synopsis of the stratigraphical and geographical distribution of the group | date = 1963 | journal = Lunds Universitets Arsskrift | volume = 59 | issue = 1 | pages = 1–59 | url = http://paleoarchive.com/literature/Persson1963-RevisionClassificationPlesiosauria.pdf | access-date = November 17, 2017 | archive-url = https://web.archive.org/web/20171118222539/http://paleoarchive.com/literature/Persson1963-RevisionClassificationPlesiosauria.pdf | archive-date = November 18, 2017 | url-status = live }}</ref> In 1995 Nathalie Bardet and [[Pascal Godefroit]] also recognized it as an elasmosaurid, albeit indeterminate.<ref name="bardet1995">{{cite journal | last1 = Bardet | first1 = N. | last2 = Godefroit | first2 = P. | title = ''Plesiosaurus houzeaui'' <small>Dollo, 1909</small> from the Upper Campanian of Ciply (Belgium) and a review of the Upper Cretaceous plesiosaurs from Europe | date = 1995 | journal = Bulletin de l'Institut Royal des Sciences Naturelles de Belgique | volume = 65 | pages = 179–186 | url = http://biblio.naturalsciences.be/rbins-publications/bulletin-of-the-royal-belgian-institute-of-natural-sciences-earth-sciences/bulletin-of-the-royal-belgian-institute-of-natural-sciences-earth-sciences/bardet_plesiosaurus_1995 | access-date = November 17, 2017 | archive-url = https://web.archive.org/web/20171118221844/http://biblio.naturalsciences.be/rbins-publications/bulletin-of-the-royal-belgian-institute-of-natural-sciences-earth-sciences/bulletin-of-the-royal-belgian-institute-of-natural-sciences-earth-sciences/bardet_plesiosaurus_1995 | archive-date = November 18, 2017 | url-status = live }}</ref>

[[File:The Osteology of the Reptiles p139.png|thumb|right|alt=Drawing of two bony flippers attached to plated bones of the pectoral girdle|Pectoral girdle and front paddles of a juvenile [[elasmosaurid]] originally assigned to ''E.{{nbsp}}serpentinus'']]
Cope discovered another elasmosaurid skeleton in 1876. He named it as a new species, ''E.{{nbsp}}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.{{nbsp}}orientalis'' from the black shale of the "Cretaceous bed No.{{nbsp}}4"; he excavated it with the help of George B. Cledenning and Capt. Nicholas Buesen.<ref name="cope1877">{{cite journal | last1 = Cope | first1 = E.D. | title = Report on the Geology of the Region of the Judith River, Montana: And on Vertebrate Fossils Obtained on Or Near the Missouri River | date = 1877 | volume = 3 | issue = 3 | journal = Bulletin of the United States Geological and Geographical Survey of the Territories | url = https://www.biodiversitylibrary.org/item/98702#page/643/mode/1up | pages = 565–598 | access-date = November 25, 2017 | archive-url = https://web.archive.org/web/20171201035534/https://www.biodiversitylibrary.org/item/98702#page/643/mode/1up | archive-date = December 1, 2017 | url-status = live }}</ref> In 1943 Welles removed ''E.{{nbsp}}serpentinus'' from ''Elasmosaurus'', and placed it in a new genus, ''Hydralmosaurus''.<ref name="welles1943">{{cite journal | last = Welles | first = S.P. | title = Elasmosaurid plesiosaurs with description of new material from California and Colorado | journal = Memoir of the University of California | volume = 13 | pages = 125–254 | date = 1943}}</ref> Subsequently, all ''Hydralmosaurus'' specimens were moved to ''[[Styxosaurus]]'' in 2016, rendering the former a ''nomen dubium''.<ref name="otero2016">{{cite journal | last1 = Otero | first1 = R.A. | date = 2016 | title = Taxonomic reassessment of ''Hydralmosaurus'' as ''Styxosaurus'': new insights on the elasmosaurid neck evolution throughout the Cretaceous | journal = PeerJ | volume = 4 | page = e1777 | doi = 10.7717/peerj.1777 | pmid = 27019781 | pmc = 4806632 | doi-access = free }}</ref> Williston published a figure of another ''E. serpentinus'' specimen in 1914;<ref name="williston1914">{{cite book | last1 = Williston | first1 = S.W. | title = Water Reptiles of the Past and Present | url = https://archive.org/details/waterreptilesofp00will | chapter = Sauropterygia | chapter-url = https://archive.org/stream/waterreptilesofp00will#page/86/mode/2up | page = [https://archive.org/details/waterreptilesofp00will/page/86 86] | date = 1914 | location = Chicago | publisher = University of Chicago Press | access-date = November 17, 2017 | archive-url = https://web.archive.org/web/20150418002133/https://archive.org/details/waterreptilesofp00will | archive-date = April 18, 2015 | url-status = live }}</ref> [[Elmer S. Riggs|Elmer Riggs]] formally described it in 1939.<ref name="riggs1939">{{cite journal|doi=10.5962/bhl.title.5289|title=A specimen of ''Elasmosaurus serpentinus''|date=1939|last1=Riggs|first1=E.S.|journal=Geological Series of the Field Museum of Natural History|series=Publication. Field Museum of Natural History |volume=6|issue=25|url=https://www.biodiversitylibrary.org/item/25222#page/5/mode/1up|pages=385–391|doi-access=free|access-date=November 17, 2017|archive-url=https://web.archive.org/web/20171201031202/https://www.biodiversitylibrary.org/item/25222#page/5/mode/1up|archive-date=December 1, 2017|url-status=live}}</ref> Welles moved this specimen to the new genus and species ''Alzadasaurus riggsi'' in 1943.<ref name="welles1943"/> [[Kenneth Carpenter]] reassigned it to ''[[Thalassomedon haningtoni]]'' in 1999;<ref name=Carpenter1999/> Sachs, Johan Lindgren, and Benjamin Kear noted that the remains represented a juvenile and were significantly distorted, and preferred to retain it as a ''nomen dubium'' in 2016.<ref name="sachs2016">{{cite conference | last1 = Sachs | first1 = S. | last2 = Lindgren | first2 = J. | last3 = Kear | first3 = B.P. | title = Re-description of ''Thalassomedon haningtoni'' – an elasmosaurid from the Cenomanian of North America | conference = 5th Triennial Mosasaur Meeting – A Global Perspective on Mesozoic Marine Amniotes | location = Uppsala | url = https://www.researchgate.net/publication/303446624 | publisher = Museum of Evolution, Uppsala University | book-title = Abstracts and Programs | date = 2016}}</ref>

Subsequently, a series of 19 neck and back vertebrae from the [[Big Bend Dam|Big Bend]] region of the Missouri{{snd}}part of the Pierre Shale formation{{snd}}were found by John H. Charles. Cope, upon receiving the bones at the Academy of Natural Sciences, considered them yet another species of ''Elasmosaurus''. The vertebrae were, according to Cope, the shortest among members of the genus (approaching ''Cimoliasaurus'' in this condition), but he still considered them as belonging to ''Elasmosaurus'' due to their compressed form. He named it ''E.{{nbsp}}intermedius'' in 1894.<ref name="cope1894">{{cite journal | last1 = Cope | first1 = E.D. | title = On the Structure of the Skull in the Plesiosaurian Reptilia, and on Two New Species from the Upper Cretaceous | journal = Proceedings of the American Philosophical Society | volume = 33 | issue = 144 | pages = 109–113 | date = 1894 | jstor = 983364 | url = https://www.biodiversitylibrary.org/item/94449#page/137/mode/1up}}</ref> However, in his 1906 revision of North American plesiosaurs, Williston regarded the vertebrae as "all more or less mutilated", and found no distinct differences between the remains of ''E.{{nbsp}}intermedius'' and ''E.{{nbsp}}platyurus''.<ref name="williston1906"/> In 1952 Welles opined that, if ''E.{{nbsp}}intermedius'' was valid, "it must be referred to a pliosaurian genus";<ref name="welles1952">{{cite journal | ref = welles-1952 | last = Welles | first = S. P. | title = A review of North American Cretaceous elasmosaurs | journal = University of California Publications in the Geological Sciences | volume = 29 | issue = 3 | pages = 47–144 | date = 1952 }}</ref> however, he proceeded to label it a ''nomen dubium'' in 1962.<ref name="welles1962"/> Three shorter vertebrae found alongside ''E.{{nbsp}}intermedius'', assigned by Cope to the new genus and species ''Embaphias circulosus'',<ref name="cope1894"/> were also considered by Welles to be a ''nomen dubium'' in 1962.<ref name="welles1962"/>

Williston named a number of other new ''Elasmosaurus'' species in his 1906 revision.<ref name="everhart2006">{{cite journal | last1 = Everhart | first1 = M.J. | title = The occurrence of elasmosaurids (Reptilia: Plesiosauria) in the Niobrara Chalk of Western Kansas | journal = Paludicola | date = 2006 | volume = 5 | issue = 4 | pages = 170–183 | url = https://www.researchgate.net/publication/40662835}}</ref> In 1874 he and Mudge discovered a specimen in Plum Creek, Kansas.<ref name="williston1906"/> While he initially assigned it in 1890 to a new species of ''Cimoliasaurus'', ''C.{{nbsp}}snowii'',<ref name="williston1890">{{cite journal | last1 = Williston | first1 = S.W. | title = Structure of the Plesiosaurian Skull | date = 1890 | journal = Science | volume = 16 | issue = 405 | pages = 262 | doi = 10.1126/science.ns-16.405.262 | pmid = 17829759 | bibcode = 1890Sci....16Q.262B | s2cid = 42251402 | url = https://zenodo.org/record/1448321 }}</ref> he subsequently recognized the elasmosaurid nature of its [[humerus]] and [[coracoid]]s. Thus, he renamed the species ''E.{{nbsp}}snowii''. A second specimen, discovered by Elias West in 1890, was also assigned by him to ''E.{{nbsp}}snowii''.<ref name="williston1906"/> In 1943 Welles moved ''E.{{nbsp}}snowii'' to its own genus, ''Styxosaurus'',<ref name="welles1943"/> where the species has remained. However, the West specimen was assigned to ''Thalassiosaurus ischiadicus'' (see below) by Welles in 1952;<ref name="welles1952"/> Carpenter returned it to ''S.{{nbsp}}snowii'' in 1999.<ref name=Carpenter1999/><ref name="everhart2006"/> Williston also reassigned the species ''E.{{nbsp}}ischiadicus'' from the genus ''[[Polycotylus]]'', where he had initially placed it when he named it in 1903. The type remains were discovered by him in the same 1874 expedition with Mudge. Williston assigned another specimen discovered by Mudge and H.{{nbsp}}A. Brous in 1876.<ref name="williston1906"/> In 1943 both specimens were assigned to the new genus ''Thalassiosaurus'' by Welles,<ref name="welles1943"/> who then assigned the latter to the new genus and species ''Alzadasaurus kansasensis'' in 1952.<ref name="welles1952"/> Glenn Storrs considered both to be indeterminate elasmosaurids in 1999;<ref name="storrs1999">{{cite journal | last1 = Storrs | first1 = G.W. | title = An examination of Plesiosauria (Diapsida: Sauropterygia) from the Niobrara Chalk (Upper Cretaceous) of central North America | journal = University of Kansas Paleontological Contributions | volume = 11 | date = 1999 | pages = 1–15 | url = https://www.academia.edu/3012858}}</ref> in the same year, Carpenter assigned both to ''Styxosaurus snowii''.<ref name=Carpenter1999/><ref name="everhart2006"/>

[[File:North American Plesiosaurs Elasmosaurus, Cimoliasaurus, and Polycotylus Plate 4.png|thumb|alt=Black and white photo of various bones|left|Remains of ''E. nobilis'' (now ''[[Styxosaurus snowii]]'')]]
An elasmosaurid specimen was found by Handel Martin in [[Logan County, Kansas]] in 1889. Williston named this as a new species, ''E.{{nbsp}}(?){{nbsp}}marshii''. He bore reservations about its referral to the genus, and he recognized that it possibly pertained to another genus.<ref name="williston1906"/> In 1943 Welles moved ''E.{{nbsp}}(?){{nbsp}}marshii'' to a genus of its own, ''Thalassonomosaurus'';<ref name="welles1943"/> however, Carpenter sunk ''T.{{nbsp}}marshii'' into ''Styxosaurus snowii'' in 1999.<ref name=Carpenter1999/> Another species, ''E.{{nbsp}}nobilis'', was named by Williston from very large remains discovered by Mudge in 1874 in [[Jewell County, Kansas]].<ref name="williston1906"/> Welles named ''E.{{nbsp}}nobilis'' as a species of ''Thalassonomosaurus'', ''T.{{nbsp}}nobilis'', in 1943,<ref name="welles1943"/> but it too was considered to be part of ''S.{{nbsp}}snowii'' by Carpenter.<ref name=Carpenter1999/> Finally, two exceptionally large dorsal vertebrae collected by [[Charles Hazelius Sternberg|Charles Sternberg]] in 1895 were named ''E.{{nbsp}}sternbergii'' by Williston, but were considered indeterminate by Storrs.<ref name="everhart2006"/><ref name="storrs1999"/> Williston mentioned three additional ''Elasmosaurus'' species, which he would figure and describe at a later date.<ref name="williston1906"/> He again made reference to a new species of ''Elasmosaurus'', from Kansas, in 1908.<ref name="willistion1908">{{cite journal | last1 = Williston | first1 = S.W. | title = North American Plesiosaurs: ''Trinacromerum'' | journal = Journal of Geology | volume = 16 | issue = 8 | date = 1908 | pages = 715–736 | jstor = 30068152 | doi = 10.1086/621573 | bibcode = 1908JG.....16..715W | url = https://zenodo.org/record/1431449 | doi-access = free | access-date = June 26, 2019 | archive-url = https://web.archive.org/web/20200412185908/https://zenodo.org/record/1431449 | archive-date = April 12, 2020 | url-status = live }}</ref>

Several [[Russia]]n species, based on poorly preserved vertebral remains, were assigned to ''Elasmosaurus'' by Nikolay N. Bogolubov in 1911. One was ''E.{{nbsp}}helmerseni'', which was first described by W.{{nbsp}}Kiprijanoff in 1882 from Maloje Serdoba, [[Saratov]], as ''Plesiosaurus helmerseni''. Some material from [[Scania]], Sweden, was assigned to ''P. helmerseni'' in 1885 by H.{{nbsp}}Schröder.<ref name="persson1959">{{cite journal | last1 = Persson | first1 = P.O. | title = Reptiles from the Senonian (U. Cret.) of Scania (S. Sweden) | journal = Arkiv för Mineralogi och Geologi | volume = 2 | issue = 35 | date = 1959 | pages = 431–519 | url = http://paleoarchive.com/literature/Persson1959-ReptilesSenonianScania.pdf | access-date = November 19, 2017 | archive-url = https://web.archive.org/web/20171201030943/http://paleoarchive.com/literature/Persson1959-ReptilesSenonianScania.pdf | archive-date = December 1, 2017 | url-status = live }}</ref> Vertebral and limb remains<ref name="pravoslavlev1918">{{cite journal | last1 = Pravoslavlev | first1 = P.A. | date = 1918 | title = Геологическое распространенiе эласмозавровъ | trans-title = Geological distribution of ''Elasmosaurus'' | journal = Bulletin of the Russian Academy of Sciences | volume = 12 | series = VI | issue = 17 | pages = 1955–1978 | url = http://www.mathnet.ru/php/archive.phtml?wshow=paper&jrnid=im&paperid=6011&option_lang=rus | language = ru | access-date = November 18, 2017 | archive-url = https://web.archive.org/web/20171201033259/http://www.mathnet.ru/php/archive.phtml?wshow=paper&jrnid=im&paperid=6011&option_lang=rus | archive-date = December 1, 2017 | url-status = live }}</ref> from [[Kursk]] initially assigned by Kiprijanoff to ''P.{{nbsp}}helmerseni'' were also moved by Bogolubov to the new species ''E.{{nbsp}}kurskensis'', which he considered to be "identical with ''Elasmosaurus'' or related to it". He also named ''E.{{nbsp}}orskensis'', based on "very large" neck and tail vertebra remains from Konopljanka, [[Orenburg]]; and ''E.{{nbsp}}serdobensis'', based on a single neck vertebra from Maloje Serdoba.<ref name="bogolubov1912">{{cite journal | last1 = Bogolubov | first1 = N.N. | date = 1912 | trans-title = The occurrence of ''Elasmosaurus'' and ''Polycotylus'' in Russian deposits | title = Sur la présence de l{{'}}''Elasmosaurus'' et du ''Polycotylus'' dans les dépots de la Russie | language = French | journal = Annuaire Géologique et Minéralogique de la Russie | volume = 14 | pages = 174–176 | translator-last1 = Wist | translator-first1 = W | url = http://paleoglot.org/files/Bogolubow%201912.pdf | access-date = November 18, 2017 | archive-url = https://web.archive.org/web/20181005180343/https://paleoglot.org/files/Bogolubow%201912.pdf | archive-date = October 5, 2018 | url-status = live }}</ref> However, the validity of all these species has been questioned. Welles considered ''E.{{nbsp}}kurskensis'' as an indeterminate plesiosaur in 1962.<ref name="welles1962"/> Persson noted in a 1959 review of the Swedish ''"E."{{nbsp}}helmerseni'' material that, while the species was probably closely related to ''Elasmosaurus'' proper, it was too fragmentary for this hypothesis to be assessed;<ref name="persson1959"/> he later remarked in 1963 that, regarding the latter three species, "their generic and specific definition is questionable", although he declined to specifically label them as invalid on account of not having seen the fossil material.<ref name="persson1963"/> Similarly, in 1999, Evgeniy Pervushov, Maxim Arkhangelsky, and Alexander Ivanov considered ''E.{{nbsp}}helmerseni'' to be an indeterminate elasmosaurid.<ref name="pervushov1999">{{cite book | last1 = Pervushov | first1 = E. | last2 = Arkhangelsky | first2 = M.S. | last3 = Ivanov | first3 = A.V. | trans-title = Catalog of the locations of the remains of sea reptiles in the Jurassic and Cretaceous of the Lower Volga Region | doi = 10.13140/RG.2.1.5178.3760 | trans-chapter = Sauropterygia | pages = 28–34 | chapter = Завроптеригии | title = Каталог местонахождений остатков морских рептилий в юр ских и меловых отложениях Нижнего Поволжья | date = 1999 | publisher = Saratov State University Press | location = Saratov | chapter-url = https://www.researchgate.net/publication/288991642}}</ref> In 2000 Storrs, Archangelsky, and Vladimir Efimov concurred with Welles on ''E.{{nbsp}}kurskensis'', and labelled ''E.{{nbsp}}orskensis'' and ''E.{{nbsp}}serdobensis'' as indeterminate elasmosaurids.<ref name="storrs2000"/>

Two additional Russian species were described by subsequent authors. [[Anatoly Riabinin]] described a single phalanx from a flipper in 1915 as ''E.{{nbsp}}(?){{nbsp}}sachalinensis''; the species was named after the island of [[Sakhalin]], where N.{{nbsp}}N. Tikhonovich found it in 1909.<ref name="averianov2005"/> However, this specimen cannot be identified more specifically than an indeterminate elasmosaurid, which was followed by Persson<ref name="persson1963"/> and Pervushov and colleagues.<ref name="pervushov1999"/> Storrs, Arkhangelsky, and Efimov were less specific, labelling it as an indeterminate plesiosaur;<ref name="storrs2000">{{cite book | last1 = Storrs | first1 = G.W. | last2 = Arkhangelsky | first2 = M.S. | last3 = Efimov | first3 = V.M. | chapter = Mesozoic marine reptiles of Russia and other former Soviet republics | title = The Age of Dinosaurs in Russia and Mongolia | editor1-last = Benton | editor1-first = M.J. | editor2-last = Shishkin | editor2-first = M.A. | editor3-last = Unwin | editor3-first = D.M. | editor4-last = Kurochkin | editor4-first = E.N. | chapter-url = https://books.google.com/books?id=NzVGpo3M998C&pg=PA187 | isbn = 978-0-521-55476-3 | date = 2000 | publisher = Cambridge University Press | location = Cambridge | url = https://books.google.com/books?id=NzVGpo3M998C | pages = 187–210}}</ref> this classification was followed by Alexander Averianov and Vasilii Popov in 2005.<ref name="averianov2005">{{cite journal | last1 = Averianov | first1 = A. O. | last2 = Popov | first2 = V. K. | s2cid = 44328986 | title = The first plesiosaur from the Primorye krai | journal = Doklady Biological Sciences | date = 2005 | volume = 401 | issue = 1 | pages = 133–135 | doi = 10.1007/s10630-005-0056-3 | pmid = 16003869 | url = http://doc.rero.ch/record/16185/files/PAL_E3392.pdf }}</ref> Then, in 1916, [[Pavel Pravoslavlev|Pavel A. Pravoslavlev]] named ''E.{{nbsp}}amalitskii'' from the [[Don River (Russia)|Don River]] region, based on a specimen containing vertebrae, limb girdles, and limb bones. Persson considered it a valid species, and a relatively large member of the elasmosaurids;<ref name="persson1963"/> however, like ''E.{{nbsp}}(?){{nbsp}}sachalinensis'', Pervushov and colleagues considered ''E.{{nbsp}}amalitskii'' an indeterminate elasmosaurid.<ref name="pervushov1999"/>

[[File:Mauisaurus.jpg|thumb|alt=Drawing of various bones|right|Remains of ''E. haasti'' (now ''[[Mauisaurus|Mauisaurus haasti]]'')]]
In a 1918 review of the geographic distribution and evolution of ''Elasmosaurus'', Pravoslavlev provisionally assigned three other previously named species to ''Elasmosaurus'';<ref name="pravoslavlev1918"/> his taxonomic opinions have not been widely followed. One of these was ''E.{{nbsp}}chilensis'', based on the [[Chile]]an ''Plesiosaurus chilensis'' named from a single tail vertebra by [[Claude Gay]] in 1848.<ref name="gay1848">{{cite book | last1 = Gay | first1 = C. | series = Historia Física y Política de Chile [Physical and Political History of Chile] | title = Zoologia, Vol. 2 | pages = 130–136 | chapter-url = https://www.biodiversitylibrary.org/item/130101#page/130/mode/1up | publisher = Imprenta Maulde y Renou | location = Paris |date = 1848 | trans-title = Zoology, Vol. 2 | chapter = Reptiles Fosiles | volume = 2 | trans-chapter = Fossil Reptiles| language =es}}</ref> In a work published in 1889, [[Richard Lydekker]] assigned this species to ''Cimoliasaurus''.<ref name="lydekker1889">{{cite book | last1 = Lydekker | first1 = R. | title = Catalogue of the fossil Reptilia and Amphibia in the British Museum. Part II | publisher = Printed by order of the Trustees | place = London | page = 222 | date = 1889 | url = https://www.biodiversitylibrary.org/item/125714#page/252/mode/1up }}</ref> Wilhelm Deecke moved ''chilensis'' to ''[[Pliosaurus]]'' in 1895,<ref name="deecke1895">{{cite journal | last1 = Deecke | first1 = W. | title = Ueber Saurierreste aus den Quiriquina−Schichten | trans-title = Concerning Dinosaur Remains from the Quiriquina Strata | date = 1895 | journal = Beiträge zur Geologie und Palae<!--JCW-CleanerBot-->ontologie von Südamerika | volume = 14 | pages = 32–63 |url = https://books.google.com/books?id=AgBGAQAAMAAJ&pg=PA32 | language = de}}</ref> a classification which was acknowledged by Pravoslavlev. [[Edwin H. Colbert|Edwin Colbert]] later assigned the type vertebra in 1949 to a [[pliosauroidea|pliosauroid]], and also assigned other assigned remains to indeterminate elasmosauroids;<ref name="colbert1949">{{cite journal | title = A new Cretaceous plesiosaur from Venezuela | last1 = Colbert | first1 = E.H. | journal = American Museum Novitates | issue = 1420 | pages = 1–22 | date = 1949| citeseerx = 10.1.1.1033.3285 }}</ref><ref name="otero2010">{{cite journal | last1 = Otero | first1 = R.A. | last2 = Soto-Acuña | first2 = S. | last3 = Rubilar-Rogers | first3 = D. | title = Presence of ''Mauisaurus'' in the Maastrichtian (Late Cretaceous) of central Chile | journal = Acta Palaeontologica Polonica | date = 2010 | volume = 55 | issue = 2 | pages = 361–364 | doi = 10.4202/app.2009.0065 | doi-access = free }}</ref> the type vertebra was recognized as potentially belonging to ''[[Aristonectes|Aristonectes parvidens]]'' by José O'Gorman and colleagues in 2013.<ref name="ogorman2013">{{cite journal | first1 = J.P. | last1 = O'Gorman | first2 = Z. | last2 = Gasparini | first3 = L. | last3 = Salgado | title = Postcranial morphology of ''Aristonectes'' (Plesiosauria, Elasmosauridae) from the Upper Cretaceous of Patagonia and Antarctica | journal = Antarctic Science | volume = 25 | issue = 1 | date = 2013 | doi = 10.1017/S0954102012000673 | pages = 71–82 | bibcode = 2013AntSc..25...71O | hdl = 11336/11188 | s2cid = 128417881 | hdl-access = free }}</ref> Another was ''E.{{nbsp}}haasti'', originally ''[[Mauisaurus|Mauisaurus haasti]]'', named by [[James Hector]] in 1874 based on remains found in [[New Zealand]].<ref name="hector1874">{{cite journal|last1=Hector|first1=J.|title=On the fossil Reptilia of New Zealand|journal=Transactions and Proceedings of the Royal Society of New Zealand|date=1874|volume=6|pages=333–358|url=https://www.biodiversitylibrary.org/item/108479#page/407/mode/1up}}</ref> Although its validity was supported for a considerable time, ''M.{{nbsp}}haasti'' is regarded as a ''nomen dubium'' as of 2017.<ref name="hiller2017">{{cite journal | last1 = Hiller | first1 = N. | last2 = O'Gorman | first2 = J.P. | last3 = Otero | first3 = R.A. | last4 = Mannering | first4 = A.A. | title = A reappraisal of the Late Cretaceous Weddellian plesiosaur genus ''Mauisaurus'' <small>Hector, 1874</small> | journal = New Zealand Journal of Geology and Geophysics | date = 2017 | volume = 60 | issue = 2 | doi = 10.1080/00288306.2017.1281317 | pages = 112–128 | bibcode = 2017NZJGG..60..112H | s2cid = 132037930 }}</ref> Pravoslavlev recognized another species from New Zealand, ''E.{{nbsp}}hoodii'', named by Owen in 1870 as ''Plesiosaurus hoodii'' based on a neck vertebra.<ref name="owen1870">{{cite journal | last1 = Owen | first1 = R. | title = Notice of some Saurian Fossils discovered by J. H. Hood, Esq., at Waipara, Middle Island, New Zealand | journal = Geological Magazine | volume = 7 | issue = 68 | date = 1870 | pages = 49–53 | doi = 10.1017/S0016756800209205 | bibcode = 1870GeoM....7...49O | url = https://zenodo.org/record/1810670 }}</ref> Welles recognized it as a ''nomen dubium'' in 1962;<ref name="welles1962"/> [[Joan Wiffen]] and William Moisley concurred in a 1986 review of New Zealand plesiosaurs.<ref name="wiffen1986">{{cite journal | last1 = Wiffen | first1 = J. | last2 = Moisley | first2 = W.L. | title = Late Cretaceous reptiles (Families Elasmosauridae and Pliosauridae) from the Mangahouanga Stream, North Island, New Zealand | journal = New Zealand Journal of Geology and Geophysics | volume = 29 | issue = 2 | date = 1986 | doi = 10.1080/00288306.1986.10427535 | pages = 205–252| bibcode = 1986NZJGG..29..205W }}</ref>

In 1949 Welles named a new species of ''Elasmosaurus'', ''E.{{nbsp}}morgani''. It was named from a well-preserved skeleton found in [[Dallas County, Texas]].<ref name="welles1949">{{cite journal | last1 = Welles | first1 = S.P. | title = A new elasmosaur from the Eagle Ford Shale of Texas | journal = Fondren Science Series | volume = 1 | date = 1949 | pages = 1–40 | url = https://sites.smu.edu/shulermuseum/publication_pdfs/fondren_sci/v1-Welles1949.pdf | access-date = November 19, 2017 | archive-url = https://web.archive.org/web/20171201043438/https://sites.smu.edu/shulermuseum/publication_pdfs/fondren_sci/v1-Welles1949.pdf | archive-date = December 1, 2017 | url-status = live }}</ref> However, part of the specimen was accidentally thrown out during the relocation of the [[Southern Methodist University]]'s paleontological collections.<ref name="sachs2015"/> Welles recognized ''E.{{nbsp}}morgani''{{'}}s similarity to ''E.{{nbsp}}platyurus'' in its shoulder girdle, but maintained it as a separate species due to its shorter neck and more robust rear neck vertebrae.<ref name="welles1949"/> In 1997 Carpenter reconsidered the differences between the two species, and found them sufficient to place ''E.{{nbsp}}morgani'' in its own genus, which he named ''[[Libonectes]]''.<ref name="carpenter1997">{{cite book | last1 = Carpenter | first1 = K. | date = 1997 | chapter = Comparative cranial anatomy of two North American plesiosaurs | title = Ancient Marine Reptiles | url = https://archive.org/details/ancientmarinerep00call | url-access = limited | editor1-first = J.M. | editor1-last = Callaway | editor2-first = E.L. | editor2-last = Nicholls | pages = [https://archive.org/details/ancientmarinerep00call/page/n237 191]–216 | location = San Diego | publisher = Academic Press | doi = 10.1016/B978-012155210-7/50011-9| isbn = 9780121552107 }}</ref> Despite its reassignment and the loss of its material, ''L.{{nbsp}}morgani'' is often considered an archetypal elasmosaurid. Data based on these lost elements were unquestionably accepted in subsequent [[phylogeny|phylogenetic analyses]], until a redescription of the surviving elements was published by Sachs and Benjamin Kear in 2015.<ref name="sachs2015">{{cite journal | last1 = Sachs | first1 = S. | last2 = Kear | first2 = B.P. | title = Postcranium of the paradigm elasmosaurid plesiosaurian ''Libonectes morgani'' <small>(Welles, 1949)</small> | journal = Geological Magazine | volume = 152 | issue = 4 | date = 2015 | pages = 694–710 | doi = 10.1017/S0016756814000636 | bibcode = 2015GeoM..152..694S | s2cid = 83740713 }}</ref>

Persson assigned another species to ''Elasmosaurus'' alongside his 1959 description of ''"E."{{nbsp}}helmerseni'' remains from Sweden, namely ''E.{{nbsp}}(?){{nbsp}}gigas''. It was based on Schröder's ''Pliosaurus{{nbsp}}(?) gigas'', named in 1885 from two dorsals; one was found in [[Prussia (region)|Prussia]], the other in Scania. While they were incomplete, Persson recognized that their proportions and the shape of their articular ends differed greatly from pliosauroids, and instead agreed well with elasmosaurids. Given that, at the time of Persson's writing, "there [was] nothing to contradict that they are nearest akin to ''Elasmosaurus''", he assigned them to ''Elasmosaurus'' "with hesitation". Theodor Wagner had previously assigned ''gigas'' to ''Plesiosaurus'' in 1914.<ref name="persson1959"/> As of 2013, this questionable attribution remains unchanged.<ref name="sorenson2013">{{cite journal | last1 = Sørensen | first1 = A.M. | last2 = Surlyk | first2 = F. | last3 = Lindgren | first3 = J. | title = Food resources and habitat selection of a diverse vertebrate fauna from the upper lower Campanian of the Kristianstad Basin, southern Sweden | date = 2013 | volume = 42 | journal = Cretaceous Research | pages = 85–92 | doi = 10.1016/j.cretres.2013.02.002 | bibcode = 2013CrRes..42...85S | url = https://www.academia.edu/5004617}}</ref> Another species from Russia, ''E.{{nbsp}}antiquus'', was named by Dubeikovskii and Ochev in 1967<ref name="storrs2000"/> from the Kamsko-Vyatsky [[phosphorite]] quarry, but Pervushov and colleagues in 1999, followed by Storrs and colleagues in 2000, reinterpreted it as an indeterminate elasmosaurid.<ref name="pervushov1999"/><ref name="storrs2000"/>