Why did sea monsters have long necks?

From the journal Science: A recently found fossil represents a new species of ancient marine reptile, and researchers think its long neck may have helped it hunt prey stealthily.
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These prehistoric marine reptiles evolved long necks by adding more vertebrae

Premium Photo A sea monster emerging from the water its long neck and head stretching upwards

Long-necked reptiles, Tanystropheus, were easily decapitated by dinosaur predators •

A new study reveals the secrets of the plesiosaur's neck, a group of predators that thrived after the end-Permian mass extinction.

Sea monsters at the time of the dinosaurs

Pliosaur discovery: Huge sea monster emerges from Dorset cliffs

Long neck dinosaur was more vulnerable to predators, scientists find

Elasmosaurus, Land of the Lost Wiki

Fossil 'sea monster' found in Antarctica was the heaviest of its kind

Fossils show ancient long-necked sea beast's 'gruesome' decapitation

Longneck, Encyclopaedia of Cryptozoology

Tanystropheus had a disproportionate neck three times its body length — but why?

Morgawr, Weird n' Wild Creatures Wiki

The Real Life Under 25 Neck Rings: Karen Long Neck Tribe Thailand

Ancient tradition of long-neck women fades as Myanmar develops

Kayan Tribe: The Unique Long Neck People Of Thailand — Guardian

A long neck? Allow yourself to be elegant

PADAUNG LONG NECK WOMEN