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

At 15 tons, the largest ever discovered elamosaur corroborates the theory that the Earth harbored a vibrant

An illustration shows an elasmosaurus swimming in turbulent waters. The Antarctic fossil is now the heaviest animal ever known in this group of prehistoric marine reptiles.

It took decades of resistance to severe weather on a small, desolate island in the Antarctic Peninsula. But now the scientists have finally discovered the heaviest elasmossaur ever known, a prehistoric marine reptile that inhabited the Cretaceous seas around the same time as the dinosaurs. The animal would have weighed about 15 tonnes, and is now one of the most complete prehistoric reptile fossils ever discovered in Antarctica.

Elasmosaurs make up a family of plesiosaurs, who represent some of the largest creatures in the Cretaceous. Plesiosaurs generally resemble large manatees, with giraffe necks and flattened heads, although they have four fins and not three.

PLESIOSSAUROS 101
Get to know the marine reptiles that dominated Earth in prehistoric times.

The team believes that the newly discovered heavyweight belongs to the genus Aristonectes, a group whose species are considered distinct from other elasmosaurs, as they differ greatly from the fossils discovered in the United States. This genus, found in the southern hemisphere, is characterized by short neck and large skull.

"That was a mystery for many years. We did not know if they were elamossaurs or not, "says José O'Gorman, a paleontologist at the National Council of Scientific and Technical Research of Argentina (Conicet), based at the La Plata Museum, near Buenos Aires. "They were like strange plesiosaurs that no one knew."

The researchers needed a more complete specimen and, as it happened, William Zinsmeister of Purdue University had discovered a possible candidate on Seymour Island – just south of the northern portion of the Antarctic Peninsula – during an expedition in 1989. However, at the time, it did not have the resources to excavate the fossil, but it informed researchers in Argentina about the discovery.

Glacial excavations

The Argentine Antarctic Institute got involved and began digging the fossil as part of its annual research expeditions, but the giant reptile was being revealed in glacial rhythm due to weather conditions and logistics.

O'Gorman, who was five years old when the fossil was discovered, began participating in such trips in 2012. It was only possible to work a few weeks in January and early February. In some years, there has been no excavation activity due to limited weather and limited resources. On days of activity, the team needed to wait for the sun to defrost the ground before it could dig, and each piece removed had to be sent by helicopter to Marambio Base, an Argentine base located a few miles away.

"Climate is one of the problems. The climate controls everything. It may be possible to work one day and the next not because of a snowstorm, "says O'Gorman.

"To begin with, the process requires a bit more effort and logistics, not to mention that it is not at all common to come across such a fossil," agrees Anne Schulp, a vertebrate paleontologist at the University of Utrecht in the Netherlands and the Naturalis Biodiversity Center, who did not participate in the survey.

A colossus between giants

The excavation finally ended in 2017, having extracted a large part of the animal's skeleton, described by O'Gorman and his colleagues in an article recently published in the scientific journal Cretaceous Research.

"We can not get the skull, but we have lots of pieces of the animal," says O'Gorman.

They estimate that the elasmosaurus, which still has no name, weighed between 11.8 and 14.8 tons, and was 12 meters long, from head to tip of tail. Whereas some previously discovered Aristonectes weighed about 11 tons, most of the elasmosaurs weighed only five tons.

"This guy is huge!" Schulp said as he looked at the photos of the bones.

He believes the work was well done and is pleased that the team did not rush to come to any conclusions – O'Gorman even hesitates to say whether the species is even of the genus Aristonectes, as new evidence can species in a different and totally new genre.

The Last Call of the Cretaceous

Schulp worked with some plesiosaurs in the Netherlands, but he claims that aquatic reptiles are very different in the southern hemisphere. The new specimen is also very interesting because it is from a time near the end of the Cretaceous period – just 30,000 years before the mass extinction event that decimated terrestrial dinosaurs about 66 million years ago.

There was probably plenty of marine life in this period to satisfy the hunger of such a large creature. So the fact that these animals continued to exist until the end of the Cretaceous is further proof that at least the aquatic world was very well until the sudden event of mass extinction.

"Even in Antarctica, there were countless Susanmossaurs living happily," says Schulp. The different morphology of the species also demonstrates that there was still specialization in this late epoch of plesiosaurs. "It is certainly an indication that t[os plesiossauros]hey have been able to increase their food repertoire in the late Cretaceous," says Schulp.

Although the exact diet of the animal can not be known without a fossilized stomach content or other evidence, O'Gorman believes they probably fed on crustaceans and smaller fish since their teeth are small.

The work on bones excavated over the past few decades has just begun. Now that the materials are in a museum, O'Gorman says there are many more researches that can be done on this prehistoric specimen.

Schulp also says that the work increases current knowledge about plesiosaurs, and he is excited to see Argentine paleontologists come back to explore and find more fossils.

"The southern hemisphere, at least as far as plesiosaurs are concerned, could certainly get more attention," he says.

As for O'Gorman, he seemed enthusiastic about the whole experience: "It was very cold, but it was really cool. It was an adventure. "

Via National Geographic
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