In Colombia and Venezuela fossils of the Megatheriidae family have been found, which are related to Sivatherium-ka fossil of a giant sloth
dating back 5.8 million years.  - National Museum and A.M. Costa Rica wire services illustrative  photo -

Published Thursday, September 10, 2020

Advances research on giant sloth
fossil found in Puntarenas

By the A.M. Costa Rica staff

Special coverage by the Efe agency and published by the National Museum on Tuesday gives the most recent advances in the study of a fossil of a giant sloth dating back 5.8 million years.

In 2013, the fossil remains were found in San Gerardo de Limoncito, in Coto Brus Canton, Puntarenas Province. It was classified as the Sivatherium species, which in the indigenous Bribri language means "Beast from the site of Sibö." Sibö is the main Bribri deity, the report said.

This fossil represents a new genus and species of giant sloth for science and, according to the research, it was probably a land animal of approximately four tons in weight and three meters high, which was a herbivore and it could ingest about half a ton of vegetation a day.

The paleontologist of the Venezuelan Institute of Scientific Research, Ascanio Rincón, who was part of the analysis, explained that the sloth is part of the Megatheriidae family and has a combination of characteristics never before seen in a fossil of this family.

"Imagine a sloth that lives in trees today but the size of an elephant with shorter front legs," Rincón said. "It was hairy and the teeth suggest it was herbivorous because it has two transverse ridges that allowed it to cut through vegetation."

The sloth is the first specimen of that family, of which there is a record that passed from South America to Central America. In Costa Rica, fossils of other giant species had been found, but from millions of more recent years.

The new species possibly comes from South America, as part of its migration to North America, known as the Great American Biotic Interchange.

However, the formation of the Isthmus of Panama has been established by geologists during the Pliocene 3 million years ago, while Sivatherium-ka is 5.8 million years old. This would allow believing that a terrestrial corridor existed during certain periods for the exchange of fauna and flora.

"Perhaps what Sibotherium-ka tells us is that the emergence of the isthmus was not in a single event but stages, it rose and it submerged, and that allowed some fauna to cross," said Rincón.

"We have to remember that 5.8 million years ago there were colder climatic conditions, then the ocean was probably much lower and there was probably an oceanic ridge that could join what is now Colombia with Costa Rica, perhaps there was a certain connection seasonal due to tidal movements," the paleontologist said.

In Colombia and Venezuela fossils of the Megatheriidae family have been found, which are related to Sivatherium-ka. For scientists, this also gives a clue to understanding the emergence and history of flora and fauna.

"Geological history will change (...) they will have to put together this puzzle of what those land passages were like that allowed these land animals to cross here," said Ana Lucía Valerio, an expert geologist in vertebrate paleontology at the National Museum.

In the excavation, the specialists found three individuals, although only some fossil parts, even though the samples were few, about 75 fragments in total, they had enough morphological information to detect that it was a new species. "We have the ankle bone that was key to compare it with other specimens from other museums; we have molars and part of the jaw," Valerio said.

In the analysis, the researchers found that the ankle bone (talus) has a very particular configuration: It is shorter and wider than the rest of it's family. "That gave us a shocking clue that we were facing something very strange," Rincón said.

Also, the teeth located in the middle between quadrangular and rectangular, as well as the position of the first tooth at its insertion in the jaw, revealed unique characteristics within the Megatheriidae family.

The discovery was made by a specialist of the National Museum, when they received a call about a child who was removing some "very strange stones" on the bank of a river, for which specialist made a visit to the site and discovered the fossils.

Valerio, together with the paleontologist of the National Institute of Learning César Laurito, began the excavations that allowed the discovery of nearly 5,000 fossils, among them horses, camels, sharks, mastodons, peccaries, as well as the unidentified sloth species.

"They were a lot of different bones, the boy had put them in boxes and had them in the backyard of the house. We looked for the place where they had taken the bones and started looking for the outcrop, after finding it we did the excavations in the dry season because it is a very dangerous place due to its active landslides," Valerio said.

All the material extracted from the site is currently part of the National Museum and now the challenge will be to search for more fossils in the valley of San Gerardo. "I think there are going to be more complete remains because of the Sivatherium- ka we have few bones that give us wonderful clues about what happened in the isthmus 5.8 million years ago," Rincón said.

Could this discovery change the traditional concepts of the American Continent evolution?
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