Elasmosauridae - Wikipedia - Recent changes [en]

In 1940 [[Theodore White]] published a hypothesis on the interrelationships between different plesiosaurian families. He considered Elasmosauridae to be closest to the Pliosauridae, noting their relatively narrow coracoids as well as their lack of interclavicles or clavicles. His diagnosis of the Elasmosauridae also noted the moderate length of the skull (i.e., a mesocephalic skull); the neck ribs having one or two heads; the scapula and coracoid contacting at the midline; the blunted rear outer angle of the coracoid; and the pair of openings (fenestrae) in the scapula–coracoid complex being separated by a narrower bar of bone compared to pliosaurids. The cited variability in the number of heads on the neck ribs arises from his inclusion of ''[[Simolestes]]'' to the Elasmosauridae, since the characteristics of "both the skull and shoulder girdle compare more favorably with ''Elasmosaurus'' than with ''[[Pliosaurus]]'' or ''[[Peloneustes]]''." He considered ''Simolestes'' a possible ancestor of ''Elasmosaurus''.<ref name="white1940">{{cite journal | first1 = T.E. | last1 = White | date = 1940 | journal = Journal of Paleontology | title = Holotype of ''Plesiosaurus longirostris'' Blake and Classification of the Plesiosaurs | volume = 14 | issue = 5 | pages = 451–467 | jstor = 1298550}}</ref> [[Oskar Kuhn]] adopted a similar classification in 1961.<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}}</ref>{{rp|4}}

In 1940 [[Theodore White]] published a hypothesis on the interrelationships between different plesiosaurian families. He considered Elasmosauridae to be closest to the Pliosauridae, noting their relatively narrow coracoids as well as their lack of interclavicles or clavicles. His diagnosis of the Elasmosauridae also noted the moderate length of the skull (i.e., a mesocephalic skull); the neck ribs having one or two heads; the scapula and coracoid contacting at the midline; the blunted rear outer angle of the coracoid; and the pair of openings (fenestrae) in the scapula–coracoid complex being separated by a narrower bar of bone compared to pliosaurids. The cited variability in the number of heads on the neck ribs arises from his inclusion of ''[[Simolestes]]'' to the Elasmosauridae, since the characteristics of "both the skull and shoulder girdle compare more favorably with ''Elasmosaurus'' than with ''[[Pliosaurus]]'' or ''[[Peloneustes]]''." He considered ''Simolestes'' a possible ancestor of ''Elasmosaurus''.<ref name="white1940">{{cite journal | first1 = T.E. | last1 = White | date = 1940 | journal = Journal of Paleontology | title = Holotype of ''Plesiosaurus longirostris'' Blake and Classification of the Plesiosaurs | volume = 14 | issue = 5 | pages = 451–467 | jstor = 1298550}}</ref> [[Oskar Kuhn]] adopted a similar classification in 1961.<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}}</ref>{{rp|4}}

[[Samuel Paul Welles]] took issue with White's classification in his 1943 revision of plesiosaurs, noting that White's characteristics are influenced by both preservation and [[ontogeny]]. He divided plesiosaurs into two superfamilies, the [[Plesiosauroidea]] and [[Pliosauroidea]], based on neck length, head size, ischium length, and the slenderness of the humerus and femur (the propodialia). Each superfamily was further subdivided by the number of heads on the ribs, and the proportions of the epipodialia. Thus, elasmosaurids had long necks, small heads, short ischia, stocky propodialia, single-headed ribs, and short epipodialia.<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> Pierre de{{nbsp}}Saint-Seine in 1955 and [[Alfred Romer]] in 1956 both adopted Welles' classification.<ref name="persson1963"/>{{rp|4}} In 1962 Welles further subdivided elasmosaurids based on whether they possessed pelvic bars formed from the fusion of the ischia, with ''Elasmosaurus'' and ''[[Brancasaurus]]'' being united in the subfamily Elasmosaurinae by their sharing of completely closed pelvic bars.<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>{{rp|4}}

[[Samuel Paul Welles]] took issue with White's classification in his 1943 revision of plesiosaurs, noting that White's characteristics are influenced by both preservation and [[ontogeny]]. He divided plesiosaurs into two superfamilies, the [[Plesiosauroidea]] and [[Pliosauroidea]], based on neck length, head size, ischium length, and the slenderness of the humerus and femur (the propodialia). Each superfamily was further subdivided by the number of heads on the ribs, and the proportions of the epipodialia. Thus, elasmosaurids had long necks, small heads, short ischia, stocky propodialia, single-headed ribs, and short epipodialia.<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 | url = https://plesiosauria.com/pdf/welles_1943_elasmosaurid_plesiosaurs.pdf}}</ref> Pierre de{{nbsp}}Saint-Seine in 1955 and [[Alfred Romer]] in 1956 both adopted Welles' classification.<ref name="persson1963"/>{{rp|4}} In 1962 Welles further subdivided elasmosaurids based on whether they possessed pelvic bars formed from the fusion of the ischia, with ''Elasmosaurus'' and ''[[Brancasaurus]]'' being united in the subfamily Elasmosaurinae by their sharing of completely closed pelvic bars.<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>{{rp|4}}

Per Ove Persson, however, considered Welles' classification too simplistic, noting in 1963 that it would, in his opinion, erroneously assign ''Cryptoclidus'', ''Muraenosaurus'', ''Picrocleidus'', and ''Tricleidus'' to the Elasmosauridae. Persson refined the Elasmosauridae to include traits such as the crests on the sides of the neck vertebrae; the hatchet-shaped neck ribs at the front of the neck; the fused clavicles; the separation of the coracoids at the rear; and the rounded, plate-like pubis. He also retained the Cimoliasauridae as separate from the Elasmosauridae, and suggested, based on comparisons of vertebral lengths, that they diverged from the Plesiosauridae in the Late Jurassic or Early Cretaceous.<ref name="persson1963"/>{{rp|7}} However, David S. Brown noted in 1981 that the variability of neck length in plesiosaurs made Persson's argument unfeasible, and moved the aforementioned genera back into the Elasmosauridae; he similarly criticized Welles' subdivision of elasmosaurids based on the pelvic bar. Brown's diagnosis of elasmosaurids included the presence of five premaxillary teeth; the ornamentation of teeth by longitudinal ridges; the presence of grooves surrounding the [[occipital condyles]]; and the broad-bodied scapulae meeting at the midline.<ref name="brown1981">{{cite journal | date = 1981 | first1 = D.S. | last1 = Brown | title = The English Upper Jurassic Plesiosauroidea (Reptilia) and a review of the phylogeny and classification of the Plesiosauria | volume = 35 | issue =4 | pages = 253–347 | url = https://www.biodiversitylibrary.org/part/83377 | journal = Bulletin of the British Museum}}</ref>{{rp|336}} In 2009, F. Robin O'Keefe and Hallie Street synonymized the Cimoliasauridae with the Elasmosauridae, noting that most of the diagnostic traits previously established to distinguish them are also found in elasmosaurids.<ref name="okeefeandstreet">{{cite journal|first1=F. R.|last1=O'Keefe|first2=H. P.|last2=Street|year=2009|title=Osteology of the cryptoclidoid plesiosaur ''Tatenectes laramiensis'', with comments on the taxonomic status of the Cimoliasauridae|url=http://www.science.marshall.edu/okeefef/PDFS/OKeefeStreet2009.pdf|journal=Journal of Vertebrate Paleontology|volume=29|issue=1|pages=48–57|doi=10.1671/039.029.0118|s2cid=31924376}}</ref>

Per Ove Persson, however, considered Welles' classification too simplistic, noting in 1963 that it would, in his opinion, erroneously assign ''Cryptoclidus'', ''Muraenosaurus'', ''Picrocleidus'', and ''Tricleidus'' to the Elasmosauridae. Persson refined the Elasmosauridae to include traits such as the crests on the sides of the neck vertebrae; the hatchet-shaped neck ribs at the front of the neck; the fused clavicles; the separation of the coracoids at the rear; and the rounded, plate-like pubis. He also retained the Cimoliasauridae as separate from the Elasmosauridae, and suggested, based on comparisons of vertebral lengths, that they diverged from the Plesiosauridae in the Late Jurassic or Early Cretaceous.<ref name="persson1963"/>{{rp|7}} However, David S. Brown noted in 1981 that the variability of neck length in plesiosaurs made Persson's argument unfeasible, and moved the aforementioned genera back into the Elasmosauridae; he similarly criticized Welles' subdivision of elasmosaurids based on the pelvic bar. Brown's diagnosis of elasmosaurids included the presence of five premaxillary teeth; the ornamentation of teeth by longitudinal ridges; the presence of grooves surrounding the [[occipital condyles]]; and the broad-bodied scapulae meeting at the midline.<ref name="brown1981">{{cite journal | date = 1981 | first1 = D.S. | last1 = Brown | title = The English Upper Jurassic Plesiosauroidea (Reptilia) and a review of the phylogeny and classification of the Plesiosauria | volume = 35 | issue =4 | pages = 253–347 | url = https://www.biodiversitylibrary.org/part/83377 | journal = Bulletin of the British Museum}}</ref>{{rp|336}} In 2009, F. Robin O'Keefe and Hallie Street synonymized the Cimoliasauridae with the Elasmosauridae, noting that most of the diagnostic traits previously established to distinguish them are also found in elasmosaurids.<ref name="okeefeandstreet">{{cite journal|first1=F. R.|last1=O'Keefe|first2=H. P.|last2=Street|year=2009|title=Osteology of the cryptoclidoid plesiosaur ''Tatenectes laramiensis'', with comments on the taxonomic status of the Cimoliasauridae|url=http://www.science.marshall.edu/okeefef/PDFS/OKeefeStreet2009.pdf|journal=Journal of Vertebrate Paleontology|volume=29|issue=1|pages=48–57|doi=10.1671/039.029.0118|s2cid=31924376}}</ref>