This elasmosaur, the heaviest of its kind, adds to the evidence of the existence of a lush marine ecosystem just before the extinction of the dinosaurs.
It has taken decades of weathering on a small desolate island off the coast of the Antarctic Peninsula. But now, scientists have unearthed the heaviest elasmosaur they know, an ancient aquatic reptile that sailed the Cretaceous seas alongside dinosaurs. The animal would have weighed up to 15 tons and is now one of the most complete ancient reptile fossils found in Antarctica to date.
The elasmosaurs, a family of plesiosaurs, represent some of the marine creatures of the Cretaceous. In general, plesiosaurs resembled huge manatees with giraffe necks and snake-like heads, although they have four fins, not three like manatees.
The team believes that this heavyweight they have described belongs to the genus Aristonectes, a group whose species are considered isolated from other elasmosaurs, as they differed greatly from fossilized specimens discovered in the United States. This genus, discovered in the southern hemisphere, is characterized by shorter necks and larger skulls.
“For years, it was a mystery … we did not know if they were elasmosaurs or not,” says José O’Gorman, a paleontologist at the National Council of Scientific and Technical Research of Argentina (CONICET) who works at the Museum of La Plata, near Buenos Aires. “They were a kind of rare plesiosaurs that nobody knew.”
The researchers needed a more complete specimen and it turned out that William Zinsmeister of Purdue University had discovered a possible candidate on Seymour Island – south of the northern tip of the Antarctic Peninsula – during a 1989 expedition. However, it did not count at that time. with the resources to excavate the fossil, but reported the discovery to a team of researchers from Argentina.
The Argentine Antarctic Institute became involved and began to dig the fossil as part of their annual summer research expeditions, but the giant reptile was discovered at a very slow pace due to time and logistics.
O’Gorman, who was five years old when the fossil was discovered, participated in the first expedition, in 2012. It was only possible to work for a few weeks in January and early February, and for years the excavation could not be produced by the weather and limited resources. In the days of activity, the team had to wait for the sun to thaw the ground before digging, and each fragment extracted from the land had to be transported by helicopter to the Argentine base of Marambio, a few kilometers away.
«Meteorology is one of the problems. Meteorology controls everything. One day you can work and the other there is a blizzard, “says O’Gorman.
“More effort and logistics need to be invested from the start, and not everyone encounters these fossils,” says Anne Schulp, a vertebrate paleontologist at the University of Utrecht and the Naturalis Biodiversity Center in the Netherlands, who did not participate. on the research.
A giant among giants
The excavation ended in 2017 and an important part of the skeleton of the animal was unearthed, which O’Gorman and his colleagues describe in a recent scientific article in Cretaceous Research .
“We do not have a skull, but we have many fragments of the specimen,” says O’Gorman.
They estimate that the elasmosaur, which still has no name, weighed between 11.8 and 14.8 tons, with a length of about 12 meters from head to tail. Although some earlier Aristonectes weighed about 11 tons, most elasmosaurs only weigh a maximum of five tons, approximately.
“It’s huge!” Exclaims Schulp as he looks at photographs of the bones.
He believes that the work has been done well and is glad that the team has not drawn hasty conclusions. In fact, O’Gorman hesitates to affirm that the species belongs definitively to the genus Aristonectes, since later tests could place the species in a new genus.
The last call of the Cretaceous
Schulp has worked with fossils of plesiosaurs from the Netherlands, but claim that aquatic reptiles are very different in the southern hemisphere. In addition, the new specimen is very interesting because it dates from a time near the end of the Cretaceous, only 30,000 years before the mass extinction erased the non-avian dinosaurs from the face of the Earth some 66 million years ago.
For such a gigantic creature to satisfy its appetite, many marine creatures must have lived in the area, so the fact that the animals continued to exist in such a late part of the Cretaceous adds to the evidence that the aquatic world, at least, it was going well until the sudden mass extinction.
“Even in Antarctica, where there were many happy elasmosaurs,” says Schulp. The different morphology of this species also demonstrates that specialization was still occurring at this late point in the existence of the plesiosaurs. “There is no doubt that it indicates that, towards the end of the Cretaceous, [the plesiosaurs] managed to expand their food repertoire,” says Schulp.
Although the exact diet of the animal without fossilized stomach contents or other tests can not be known, O’Gorman argues that it is likely to feed on crustaceans and small fish, based on the smallness of its teeth. And the analysis of the bones unearthed throughout the last decades has only just begun. Now that they are in a museum, O’Gorman says there is a lot of research to be done in this ancient specimen.
Schulp adds that the work advances our knowledge of plesiosaurs and is excited that Argentine paleontologists have returned to the field and are finding more fossils.
“The southern hemisphere – at least the plesiosaurs – needs attention,” he says.
And for his part, O’Gorman seems excited about the experience. “It was quite cold, but it also milled a lot. It was an adventure.
Source: National Geographic