Name: Aristonectes ‭(‬Best swimmer‭)‬.
Phonetic: Ah-riss-toe-nek-teez.
Named By: Cabrera‭ ‬-‭ ‬1941.
Synonyms: Morturneria.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Sauropterygia,‭ ‬Plesiosauria,‭ ‬Aristonectidae.
Species: A.‭ ‬parvidens‭ (‬type‭)‬.
Diet: Filter feeder.
Size: Uncertain due to incomplete remains.‭ ‬Skull of holotype approximately‭ ‬32-33‭ ‬centimetres 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.


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