Plesiosaurs were long-necked marine reptiles, closely related to the Pliosaurs though probably slower in the water. Their swimming speed has been estimated at 8.2km/h, which is faster than an Olympic champion, but too slow to catch a mackerel, salmon or seal. Plesiosaurs are often depicted with their neck bent into sinuous folds. In truth it was not that flexible, and no Plesiosaur ever bent its neck into the tight curve today's swans can manage. Plesiosaurs became extinct at the same time as the dinosaurs.

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