After the extinction at the end of the Cretaceous 66 million years ago, in which most dinosaurs disappeared, the Cenozoic era began. This era is popularly known as The Age of Mammals , for being the dominant group of vertebrates in terrestrial ecosystems, which replaced the Mesozoic dinosaurs. The large mammalian fauna that evolved during the Cenozoic are known as the Megafauna .
During the Cenozoic, South America was isolated, like a gigantic continent-island , and very characteristic autochthonous forms evolved. And among this fauna, the most characteristic is the one that inhabited the Pleistocene, until about 10,000 years ago.
Among the representatives of the South American Megafauna is the Megaterio , a gigantic animal related to the current sloths, and which is usually known as “giant sloth”. Megatherium was one of the largest known land mammals, weighing more than 3 tons and measuring more than 6 meters in length from head to tail. It was the largest of the known land sloths, and was among the largest known land mammals. , with a size only surpassed by the proboscideans and by some perissodactyls such as Paraceratherium . This genus is primarily known from its largest species, M. americanum . The first fossil specimen of Megatherium was discovered in 1787 by Fray Manuel Torres on the banks of the Luján River in present-day Argentina , in what is now the Province of Buenos Aires. The fossil was sent the following year to the Royal Cabinet of Natural History in Madrid , predecessor of the current National Museum of Natural Sciences. In this museum it is still preserved today with its original assembly which, although it is considered scientifically erroneous at present, is kept for its historical value, since it was the first fossil vertebrate whose skeleton was mounted and exposed. Since its first discovery, Megatherium fossils have been found in different areas of South America, in Chile, Argentina, Bolivia, Peru, Brazil, Paraguay and Uruguay.
Another large mammal characteristic of this fauna is the Toxodon or toxodon te. It was a robust mammal belonging to the extinct group of the notoungulates , and comparable in size to that of the rhinoceros, with a skeleton similar to the bovid family and a rump similar to that of the bison.
Glyptodonts were gigantic, heavily armored armadillos, with a rounded shell made up of small plates of bone that even covered their legs. They also had armored heads and tails, which could have large tubercles or spikes, such as had not been seen in terrestrial vertebrates since the extinction of the armored dinosaurs. They could exceed 3 meters in length and a meter and a half in height, and weigh more than two tons.
The Macrauchenias were large mammals belonging to the extinct order Liptoterna , with an appearance similar to that of the camelids, without being related to them at all, and whose skull had a large nostril that suggests that they may have had a kind of snout or small proboscis like those of the tapirs. They could reach 3 meters in length and 2 meters in height.
During most of the Cenozoic, the faunas of South America and North-Central America evolved independently , because they were separated by a maritime barrier at the height of the current Isthmus of Panama. When this isthmus formed about 3 million years ago , a major exchange of flora and fauna began in both directions, known as the Great American Biotic Interchange .
As a result of this exchange, some South American faunas passed to North America, as is the case of megatheria, glyptodonts or notoungulates . But North American faunas also arrived in South America, as is the case of ungulates, gomphothere mastodons or some carnivores, such as canids or saber-toothed cats.
This megafauna eventually disappeared. In the first place, due to the competition with the new forms that arrived after the exchange, and ultimately, due to the retreat of the glaciers and the effect of hunting by humans after arriving on this continent.
These faunas were very popular since their discovery (in fact the megatheria were very famous for having been found and described before the dinosaurs) and even the glyptodonts were excavated and studied by Charles Darwin himself, who compared them with the current armadillos, whom he considered his descendants when articulating his proposal for Evolution through Natural Selection.
How much we humans have to do with their extinction is still a debated topic, like many other topics that continue to be studied in Quaternary paleontology and prehistoric studies.
References:
Belinchón, M. et al. 2009. Chronicles of fossils: the paleontological collections of the Museum of Natural Sciences of Valencia. City Hall of Valencia.
Fariña, R.A. et al. 2013. Megafauna: Giant Beasts of Pleistocene South America. Indiana University Press.
Dantas, M.A.T. et al. 2013. About the occurrence of Glyptodon sp. in the Brazilian intertropical region. Quaternary International. 305: 206–208.
Gascó, F. 2021. That was not in my dinosaur history book. Guadalmazán.
