It took decades of struggling with the weather on a small, desolate island off the Antarctic Peninsula. But now, scientists have finally unearthed the heaviest known elasmosaur, an ancient aquatic reptile that swam the seas of the Cretaceous period alongside the dinosaurs. The animal would have weighed as much as 15 tons, and it is now one of the most complete ancient reptile fossils ever discovered in Antarctica.
Elasmosaurs make up a family of the plesiosaurs, which represent some of the largest sea creatures of the Cretaceous. Plesiosaurs generally look a little like large manatees with giraffe necks and snake-like heads, though they have four flippers rather than a manatee’s three.
The team thinks the newly described heavyweight belongs to the genus Aristonectes, a group whose species have been seen as outliers to other elasmosaurs, since they differed so much from fossilized specimens discovered in the U.S. This genus, found in the Southern Hemisphere, is characterized by shorter necks and larger skulls.
“For years it was a mystery … we didn’t know if they were elasmosaurs or not,” says José O’Gorman, a paleontologist with the National Scientific and Technical Research Council of Argentina (CONICET) who is based at the Museum of La Plata near Buenos Aires. “They were some kind of weird plesiosaurs that nobody knew.”
They estimate that the as-yet-unnamed elasmosaur weighed between 11.8 tons and 14.8 tons, with a head-to-tail length of nearly 40 feet. While some previously known Aristonectes have weighed about 11 tons or so, most other elasmosaurs only come in at around five tons.
A lot of marine life would have needed to thrive there to satisfy the appetite of such a large creature, so the fact that these animals continued to exist so late in the Cretaceous adds to the evidence that the aquatic world, at least, was doing just fine right up until the sudden mass extinction
https://www.nationalgeographic.com/science/2019/06/fossil-sea-monster-found-antarctica-heaviest-of-its-kind-elasmosaurs/