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Thursday, 9 May 2013

The type of the PostCretaceous Plesiosaur

This passage is comparing the late Plesiosaurian genera Elasmosaurus and Cimiolasaurus: It is not certain that Elasmosaurus was a fast swimmer because its very long neck must have made it awkward. However, the other Plesiosaur was not of a type that would have gone after Elasmosaurus, it ate smallish fishes and squids instead.

Fossils of the type species for Cimoliasaurus from a geologically ambiguous stratum in New Jersey. The vertebrae are very distinctive from oyher plesiosaur vertebrae, such as those of the Elasmosaurs, and are more cupped at the ends rather than being relatively flat. This is thought to indicate a more flexible spine, and especially a more flexible neck, for the animal in life. a second find of the supposed genus was found in Alabama and initially marked as coming from Eocene (Zueglodon-bed) deposits, and was given the now-obsolete name of Discosaurus.

(Sometimes spelled as Cimoliosaurus‭)

Name: Cimoliasaurus.
Phonetic: Sim-o-le-ah-sore-us.
Named By: Joseph Liedy‭ ‬-‭ ‬1851.
Synonyms: Cimoliasaurus brevior,‭ ‬Cimoliasaurus maccoyi,‭ ‬Discosaurus,‭ ‬Oligosimus,‭ ‬Piptomerus.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Sauropterygia,‭ ‬Pleisoauria.
Species: C.‭ ‬magnus,‭ ‬C.‭ ‬valdensis,‭ ‬C.‭ ‬snowii.
Diet: Probably piscivorous.
Size: Uncertain sue to the assemblage of remains and partial incomplete preservation of many specimens.
Known locations: Europe,‭ ‬North America and Australasia.‭ *‬Possibly not an accurate representation of the genus.
Time period: Cretaceous‭ (‬sometimes credited as mid Jurassic to end of the Cretaceous‭)‬.‭ ‭*‬Possibly not an accurate representation of the genus.[**Some specimens indicated as Post-Cretaceous when originally collected, Particularly the New Jersey specimens-DD]
Fossil representation: Multiple partial and incomplete remains.‭ ‬Possibly not all indicative of the genus.

The term most often attributed to Cimoliasaurus is‭ ‘‬wastebasket taxon‭’ ‬due to the practice of some palaeontologists‭ ‬assigning otherwise unidentifiable plesiosaur bones to the genus.‭ ‬This is why geographical distribution for the genus covers Europe,‭ ‬North America,‭ ‬and Australia and New Zealand,‭ ‬while the temporal range in the past has run from the mid Jurassic to the very end of the Cretaceous period‭ (‬though sometimes the range‭ ‬is cited as Early Cretaceous to‭ ‬the end of the Maastrichtian‭)‬.
Because of this the validity of Cimoliasaurus as a genus remains dubious,‭ ‬but more may come from the remains attributed to Cimoliasaurus such as the discovery of new plesiosaur genera.‭ ‬This has happened already with the creation of the species Cimoliasaurus laramiensis by Knight in‭ ‬1900,‭ ‬which was renamed as a species of Tricleidus‭ (‬T.‭ ‬laramiensis‭) ‬by Mehl in‭ ‬1912‭ ‬before eventually being raised as a new genus called Tatenectes by O'Keefe and Wahl in‭ ‬2003.
With more in depth study it is probable that one day Cimoliasaurus may one day be cleaned up enough to get an accurate description of a specific genus.‭ ‬Such cases of‭ ‬a‭ ‬wastebasket taxon being cleaned up is nothing new,‭ ‬with one of the best known examples being that for the dinosaur Megalosaurus.
The Chilean and Antarctic Genus Aristonectes is one that was originally classified in Cimoliasaurus (in the late 1800s) and in fact includes specimens thought to have been more recent than the end of the Cretacreous-This too is disputed but I havee discussed the matter in connection with the "Patagonian Plesiosaurs" in a few cases it is thought that the area where the fossils were not even under the sea during the Cretaceous, they were thought to have been under the sea during the Paleocene and Eocene. It fed on small animals like shrimps.


Aristonectes (meaning 'best swimmer') is an extinct genus of plesiosaur from the Late Cretaceous of what is now South America and Antarctica. The type species is Aristonectes parvidens, first named by Cabrera in 1941. [Having been called called Cimiolasaurus before then]
Aristonectes has been classified variously since the 1941 description, but a 2003 review of plesiosaurs conducted by Gasparini et al. found that Aristonectes was most closely related to elasmosaurid plesiosaurs like Elasmosaurus. A similar plesiosaur, Morturneria, may be a junior synonym of Aristonectes, the study found.
Aristonectes has been recently placed within its own family, along with Tatenectes, Kaiwhekea, and Kimmerosaurus, by O'Keefe and Street (2009). Aristonectids are the sister family of the polycotylid cryptoclidoids.


  • Gasparini, Z., Bardet, N., Martin, J.E. and Fernandez, M.S. (2003) "The elasmosaurid plesiosaur Aristonectes Cabreta from the Latest Cretaceous of South America and Antarctica". Journal of Vertebrate Paleontology 23(1): 104-115
Darren Naish mentioned the problem about classification in a recent blog and I nearly had a discussion about it then, but I found the situation to be too uncertain to make any definite statements. the original Cimiolasaurus of Leidy seems to be of the same family as Aristonectes. This family has similarirties both to the Cryptoclidids and to the Elasmosaurs but is also different than both of them. Cimiolasaurus has been reported from post-Cretaceous deposits: indeed, Leidy's initial finds were from a stratum identified as Pliocene, although this was later written off as impossible. The remains of the plesiosaur were however found mixed up with the remains of a Pliocene dolphin. The other fossils from other areas should be removed from the same genus, but there are also other fossils of PostCretaceous Plesiosaurs said to come from other areas and these might well belong to the original genus. The problem is still very far from being settled.

Skeleton of a related genus presumably in the same family, with reconstructed outline.

It should be noted that fossils of this family have been taken to indicate that the creatures were more tolerant of cold climate (including Antarctica!) and to be able to tolerate either freshwater or saltwater. They are modest-sized as Plesiosaurs go, mostly in the range of 15-30 feet long as adults. This also might be all we need for our purposes in dealing with Longnecked Cryptids reported in more modern times.

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