Elasmosaurus

Elasmosaurus was not a dinosaur, but a marine reptile belonging to the plesiosaur group that dominated Cretaceous seas. With an extraordinarily elongated neck comprising 72 vertebrae — more than any other known animal — this creature patrolled the shallow Western Interior Seaway that once split North America in two. Its small head and remarkably long neck likely allowed it to approach schools of fish and squid without disturbing them with its bulky body.

The first Elasmosaurus specimen was discovered in 1867 near Fort Wallace, Kansas, by a military doctor named Theophilus Turner. He sent the bones to renowned paleontologist Edward Drinker Cope, who formally described the animal in 1868. The name means 'thin-plate reptile' in reference to the plate-like bones of its pelvic region, while the species name 'platyurus' means 'flat-tailed.'

Cope's original reconstruction contained a famous blunder: he placed the skull on the wrong end, mounting it at the tip of the short tail rather than the long neck. His rival Othniel Charles Marsh gleefully pointed out the error, fueling their legendary 'Bone Wars' feud that would shape American paleontology for decades. This embarrassing mistake haunted Cope for the rest of his career.

Only one definitive Elasmosaurus skeleton exists, and it's incomplete — portions including the pectoral and pelvic girdles have been lost since discovery. Despite this, Elasmosaurus remains the iconic elasmosaurid, representing an extreme evolutionary experiment in neck elongation that allowed these predators to thrive for millions of years.