Elasmosaurus (meaning: thin-plated lizard) had plate like bones in its pelvic girdle and was a plesiosaur with an enormously long neck that lived in the belatedly Cretaceous period.
Elasmosaurus was a reptile, but not a dinosaur. They are distinguished by having two holes in the rear upper fraction of their skulls and two holes behind the eyes, like all Diapsids.
It was about 14 metres (46 feet) in span and weighed above 2,000 kg (2.2 tons), making it the longest ever plesiosaur species. It had a big body, a tiny head and four flippers for limbs.
More than half of its length was its neck, which had more than 70 spines, more than any other animal. It had a little head with sharp teeth and most likely ate small bony fish such as belemnites (alike to squid), lepidotes and ammonites (molluscs). It swallowed little stones in order to aid its digestion. Elasmosaurus lived in the open oceans and breathed atmosphere.
Elasmosaurus swam slowly using its four paddle-like flippers in a manner like to that of modern turtles. It may have been capable to move a small bit on sandy shores, perhaps to lay its eggs.
Elasmosaurus lived during the late Cretaceous period and went extinct during the K-T mass extermination (65 million years past).
Elasmosaurus was named by paleontologist E. D. Cope in 1868 (from a fossil was establish in Wyoming, USA). Other Elasmosaurus fossils have also been establish in North America.