A giant sloth, weighing 5 or 6 tons, and whose stature could exceed twice that of a human being, was part of prehistoric Costa Rica and inhabited our lands about 7 million years ago.
A group of paleontologists works to determine their characteristics, describe their bones, compare them with others, and see if they correspond to previously described species or if they are completely new species or genres for science.
This is part of a work that started in 2003 with various trips to San Gerardo de Limoncito, in Coto Brus, about 11 kilometers from San Vito. In this area, the researchers explored for bones and fossils of different species.
For more than a decade, Ana Lucía Valerio, coordinator of the Geology section of the National Museum and César Laurito, trainer for the work of the National Apprenticeship Institute (INA) and associate researcher of the National Museum, searched and analyzed more 2,600 bone samples from Dozens of different species that appeared during the expeditions.
“When I decided to go for paleontology, nobody gave a penny to show something here. Venturing to find mammals was unthinkable. They told us ‘you are looking for bones, it does not matter much’, but the finding makes the world see again and say ‘something is happening here, something that we did not expect and that is changing the vision of biological exchange’ “, said Laurito.
A natural bridge between the North and the South
This area would be key because it is further proof that Central America served as a communication bridge for animals to cross from South America to North America and vice versa and Central America served as a bridge and as a filter to see which species pass from one place to another and how to make.
“We are talking about something very old. The Isthmus was closed as such some 3.5 million years ago, and we are talking about how these sloths lived 7 million years ago. So, how did these giant animals of South America pass to the southern zone of Costa Rica if they did not have adaptations to dive? It is possible that for a time there was a passage, a bridge of land, for these animals to cross early. This step could have existed for a short period of time. But for paleontology a short period of time could be 1 million years”, explained Laurito.
“In other words, ‘bugs’ of South America appear much earlier than expected, about 4 million sooner than expected”, he said.
In the last years, Valerio and Laurito have described different species of prehistoric horses, camels, armadillos and other types of mammals in the Tico soil. However, they had a problem with the material of the sloths, since they had no way of comparing it. This type of research in paleontology is very new in the country. For this reason, they contacted Ascanio Rincón, head of the Laboratory of Paleontology of the Venezuelan Institute of Scientific Research of the Ministry of Science and Technology, who has been studying these lazy giants of prehistory for several years.
For a few weeks, Rincon has been collaborating with the next part of the analysis of these giant animals, that is, determining what kind of sloth they are. All the bones were found in the same site as Coto Brus, but they accumulated during the different years of searching.
“This group did not cross until much later. There is no record of these animals in North America until much later, as until about 200 thousand years ago, what prevented them from crossing, or what they found here so they would have stayed longer without moving? Food was not more to the North if not here, to the center? “, wonders Rincón.
For this new analysis, all the bones of this type of animal should be taken, photographed, measured, analyzed, described and compared with other bones of other giant sloths. Thus, important aspects of these populations can be determined. “Now it is the hard work, that is, to compare it with the rest of the 14 or 15 genres that exist and determine who is closer and who looks less, or see if it is a new species”, said Rincon.
This is not easy, because it is difficult to find complete bones or skeletons, but based on what is found, they have to draw conclusions. “This is not what you see in the movies. It’s not that he just cleaned himself a little with a brush and everything appeared there. We had to chop very hard rocks to get this out, to give a lot of strength, to look a lot, sometimes some bones of some species appeared, sometimes, other bones of other species, what we have today to assemble met for several years “, explained Laurito.
Rincon added: “That is to be able to know what is happening with only 15% of the body, how to put together that puzzle, in this case, we do have material from various types of bone that help us to better understand the panorama.
The researchers reported that there are at least three individuals within the discovered bones since three bones of the same type of different sizes (ages) were found, which could indicate that they traveled in a herd, or in a family, for example, a mother with her children or neighbors. This could give more clues, not only about who they were, but how this biological exchange was made.
Although it is still difficult to know what each of the animals that are being analyzed was like, especially because they may belong to different species and genres, the specialists do have some ideas of how these giant sloths could be.
For example, it is known that they walked on the 2 floors of their hind feet and on the knuckles of their front legs. In addition, their front claws had a very large force and were possibly used to dig. In addition, due to their weight, they did not climb trees, but rather moved on the ground walking on their hind legs and used the knuckles of their front legs as support.
On the other hand, their teeth were so strong that they not only fed on leaves but also on wood and other hard materials. They had that ability to regenerate with every wear that was incurred at the time of chewing. It was even necessary that they ate that kind of food so that their teeth would wear out because these pieces grew as new tissue and if they did not have where they could grow more than necessary and cause problems.
It is known that the lazy giants had some kind of social life and that they were possibly in packs.
Within these discoveries, there might be new species for science, but they were extinct millions of years ago. They did not even live with hominids, but in 2018 their bones are in a state of conservation necessary to know about this portion of prehistoric megafauna.
“The fossil hunter does not kill his prey; he resurrects it. We resuscitate preys that we are looking for, to make people know them, too”, said Rincon.
Why is this important? Rincon was emphatic: “This type of knowledge helps us understand who we are, where we come from, and gives identity to the Isthmus. We cannot judge a book by its last page; we must see what there is before, and that is why it is necessary to study paleontology”.