Tanystropheus ("Long Vertebra") was a large, long-necked marine reptile (a member of the prolacertid family) from the Triassic. Its most striking feature was its almost-impossibly long neck and tail that almost defied the laws of physics.
With a great long neck and great long tail, Tanystropheus hardly had any body at all. Their long necks were perfect for an ambush predator. What they did was sweep that neck through the water, sweep it through a sole of fish.
Whenever Tanystropheus dropped their tails, like most modern lizards, it was an insurance policy. If they were ever attack by a predator, the predators were distracted by the tail and the Tanystrophyous could escape. And like with lizards, they grew the tail again and it didn't do them much harm, as even when they lost their tails and swam, they could swim away perfectly to get fish.