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.
This is additional taxonomy that helps us with analytics

Oldest Antarctic Sea Monster Found

Loch Ness Monster's 'long neck and short head is spotted by rational and scientific' nurse - Mirror Online

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

Researchers Discover Prehistoric Sea Monster with Snake-Like Neck and Crocodile-Like Jaw; Name It 'Snaky Crocface

Ancient Long-Necked 'Sea Monsters' Rowed Their Way to Prey

Large bodies helped extinct marine reptiles with long necks swim, study finds

190-Million-Year-Old Long-Necked Sea Monster Identified In Germany

Strange Science: Sea Monsters

Large Bodies Helped Ancient Sea Monsters With Extremely Long Necks Swim

Plesiosaur fossils are the first evidence of Jurassic vertebrates in Texas •

Sea Monsters: Prehistoric Ocean Predators - Australian National Maritime Museum

Sea Monster Sightings and the 'Plesiosaur Effect' — Tetrapod Zoology