Name: Aristonectes ‭(‬Best swimmer‭)‬.
Phonetic: Ah-riss-toe-nek-teez.
Named By: Cabrera‭ ‬-‭ ‬1941.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Sauropterygia,‭ ‬Plesiosauria,‭ ‬Aristonectidae.
Species: A.‭ ‬parvidens‭ (‬type‭), A. quiriquinensis‬.
Diet: Filter feeder.
Size: Uncertain due to incomplete remains.‭ ‬Skull of holotype approximately‭ ‬32-33‭ ‬centimetres long. Full body length roughly estimated around ten meters long.
Known locations: Antarctica,‭ ‬Argentina‭ ‬-‭ ‬Paso del Sapo Formation,‭ ‬Chile.
Time period: Maastrichtian of the Cretaceous.
Fossil representation: Three sets of remains of partial skull material,‭ ‬cervical‭ (‬neck‭) ‬vertebrae and partial limb elements.

       While the plesiosaurs are usually seen as predators of fish Aristonectes took‭ ‬the different and much more specialist path of filter feeder.‭ ‬The teeth in the jaws were very short with crowns that were less than one centimetre high.‭ ‬There were a high number of these teeth which were densely packed together in jaws that were both proportionately long and wide compared to other plesiosaur skulls.‭ ‬This was to provide Aristonectes with the largest possible‭ ‘‬catch area‭’ ‬for small aquatic invertebrates that would have been eaten in huge numbers in order to keep its body going.‭ ‬It‭’‬s likely that Aristonectes would have swallowed gastroliths like other plesiosaurs did,‭ ‬not only for ballast but grinding food in the stomach.‭ ‬In the case of Aristonectes this would mean the shells of the invertebrates that it ate so that the soft flesh within could be more easily digested.
       The most commonly used analogy for Aristonectes is its comparison to the crabeater seal‭ (‬Lobodon carcinophagus‭) ‬which lives around Antarctica.‭ ‬Despite the name crabeater seals feed mostly upon krill while taking the‭ ‬occasional fish or cephalopods.‭ ‬Krill are open water crustaceans that are similar to shrimps,‭ ‬and are especially abundant in the cooler waters of the Antarctic‭ (‬although the Cretaceous seas were warmer than todays,‭ ‬they still would have been slightly cooler towards the poles‭)‬.‭ ‬Krill today grow up to six centimetres long and gather in swarms that‭ ‬are‭ ‬measured in their hundreds of thousands.‭ ‬All an animal has to do is swim into these concentrations and sieve the water with its teeth to get a mouthful of highly nutritious sea food.‭ ‬With Aristonectes‭ ‬feeding on such small but abundant animals,‭ ‬it could avoid direct competition with the other marine reptiles that were more generalist carnivores.
       Aristonectes sits quite comfortably within its own group of the Aristonectidae,‭ ‬its wider position amongst other plesiosaurs remains uncertain.‭ ‬Wider and more recent opinion places Aristonectes as an elasmosaurid,‭ ‬but in the past it has been considered as a cryptoclidoid.‭ ‬The one thing that could help in resolving the uncertainty is new and much better preserved fossils that would allow for a complete analysis of the whole animal.

Further reading
- Un plesiosaurio nuevo del Cretáceo del Chubut. - Revista del Museo de La Plata 2(8):113-130. - A. Cabrera - 1941.
- The elasmosaurid plesiosaur Aristonectes Cabreta from the Latest Cretaceous of South America and Antarctica. - Journal of Vertebrate Paleontology 23(1): 104-115. - Z. Gasparini, N. Bardet, , J. E. martin & M. S. Fernandez - 2003.
- A postcranial skeleton of an elasmosaurid plesiosaur from the Maastrichtian of central Chile, with comments on the affinities of Late Cretaceous plesiosauroids from the Weddellian Biogeographic Province. - Cretaceous Research, 37: 89–99. - R. A. Otero, S. Soto-Acuña & D. Rubilar-Rogers - 2012.
- Aristonectes quiriquinensis sp. nov., a new highly derived elasmosaurid from the upper Maastrichtian of central Chile. - Journal of Vertebrate Paleontology 34(1):100-125. - R. A. Otero, S. Soto-Acuña, F. R. O'Keefe, J. P. O'Gorman, W. Stinnesbeck, M. E. Suárez, D. Rubilar-Rogers, C. Salazar & L. A. Quinzio-Sinn - 2014.
- Cranial anatomy of Morturneria seymourensis from Antarctica, and the evolution of filter feeding in plesiosaurs of the Austral Late Cretaceous. - Journal of Vertebrate Paleontology. - F. O'Keefe, R. Otero, S. Soto-Acuña, J. O'gorman, S. Godfrey & S. Chatterjee - 2017.
- Osteology of Aristonectes quiriquinensis (Elasmosauridae, Aristonectinae). - Journal of Vertebrate Paleontology. 38 (1). e1408638. - Rodrigo A. Otero, Sergio Soto-Acuña & Frank R. O'keefe - 2018.


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