Editing Plesiosauroidea (section)

==Behavior==
[[Image:Plesiosaurus 3DB.jpg|thumb|left|Restoration of a ''Plesiosaurus dolichodeirus'' pair, one catching a fish.]]
Unlike their pliosauroid cousins, plesiosauroids (with the exception of the Polycotylidae) were probably slow swimmers.<ref>{{cite journal | last1 = Massare | first1 = J. A. | year = 1988 | title = Swimming capabilities of Mesozoic marine reptiles: Implications for method of predation | journal = Paleobiology | volume = 14 | issue = 2| pages = 187–205 | doi=10.1017/s009483730001191x| bibcode = 1988Pbio...14..187M | s2cid = 85810360 }}</ref> It is likely that they cruised slowly below the surface of the water, using their long flexible neck to move their head into position to snap up unwary fish or [[cephalopods]]. Their four-flippered swimming adaptation may have given them exceptional maneuverability, so that they could swiftly rotate their bodies as an aid to catching prey.

Contrary to many reconstructions of plesiosauroids, it would have been impossible for them to lift their head and long neck above the surface, in the "[[swan]]-like" pose that is often shown.<ref name=":0" /><ref>{{cite journal | last1 = Henderson | first1 = D. M. | year = 2006 | title = Floating point: a computational study of buoyancy, equilibrium, and gastroliths in plesiosaurs | journal = Lethaia | volume = 39 | issue = 3| pages = 227–244 | doi=10.1080/00241160600799846| bibcode = 2006Letha..39..227H | url = http://doc.rero.ch/record/16190/files/PAL_E3399.pdf }}</ref> Even if they had been able to bend their necks upward to that degree (which they could not), gravity would have tipped their body forward and kept most of the heavy neck in the water.

On 12 August 2011, researchers from the U.S. described a fossil of a pregnant plesiosaur found on a Kansas ranch in 1987.<ref>{{cite journal|author=F. R. O’Keefe1,*, L. M. Chiappe2 |url=https://www.science.org/doi/abs/10.1126/science.1205689 |title=Viviparity and K-Selected Life History in a Mesozoic Marine Plesiosaur (Reptilia, Sauropterygia) |journal=Science |year=2011 |volume=333 |issue=6044 |pages=870–873 |publisher=Sciencemag.org |doi=10.1126/science.1205689 |pmid=21836013 |bibcode=2011Sci...333..870O |s2cid=36165835 |access-date=2011-08-15|url-access=subscription }}</ref> The plesiosauroid, ''Polycotylus latippinus'', has confirmed that these predatory marine reptiles gave birth to single, large, live offspring—contrary to other marine reptile reproduction which typically involves a large number of small babies. Before this study, plesiosauroids had sometimes been portrayed crawling out of water to lay eggs in the manner of sea turtles, but experts had long suspected that their anatomy was not compatible with movement on land. The adult plesiosaur measures {{cvt|4|m|ft}} long and the juvenile is {{cvt|1.5|m|ft}} long.<ref>{{cite web |author=Anthony King |url=http://www.cosmosmagazine.com/news/4615/ancient-sea-dragons-had-a-caring-side |title=Ancient sea dragons had a caring side |publisher=Cosmosmagazine.com |access-date=2011-08-15 |url-status=dead |archive-url=https://web.archive.org/web/20111001200222/http://www.cosmosmagazine.com/news/4615/ancient-sea-dragons-had-a-caring-side |archive-date=2011-10-01 }}</ref>