The mysteries of paleontology

How will the future look like? How much more will we dominate our reality to put it to our service? How will we face the upcoming challenges we can barely see within the darkness of our apprehension?

Although it may seem paradoxical, the science of paleontology, besides being essential for the exploration of buried treasures, has the ability to answer these questions. Those of us who cultivate this way of fulfilling the Delphic mandate about self-knowledge, look at the fossil record and see a huge collection of futures that were. We call this ensemble that could have been very different, and spanned billions of years of the history of life, “the past”. Through the irregular prism of our tool we appreciate the rarity of organisms that disappeared without any apocalyptic sounds, we amaze ourselves with the few that remain constant through the immensity of time, we plunge into the catastrophic spectacular nature of the extinctions that put an end to the dominance of those then powerful, we wonder inevitably what role do humans have in the ongoing drama of the biodiversity loss and whether we can, with all the evolutionary success provided to us by contingency, escape the fate suffered by trilobites and dinosaurs.

Some of all this is taught by the megafauna, with the magnificence of its giant strange species that disappeared only an instant ago in geologic time. Some of all this can be found in the necessarily incomplete key to the understanding of an extraordinary fossil site, the one at Arroyo del Vizcaíno. Some of all this we dare to share here, with the hope that the resurrection in our minds of the past and its extinct life forms will help us enjoy the pleasure of becoming wiser.

What is a fossil?

A fossil can be defined as the remains of past organisms, generally of their hard skeletons, rarely of their soft parts. But that is not all, the remains found as a result of these organisms’ activities are also considered fossils, and therefore footprints, pollen grains and nests among others, should be included in the definition. How long do we have to rewind time to get to that “past” written in the definition? By convention, a somewhat arbitrary limit of 10,000 years is considered accurate, which conveniently matches the end of the last Ice Age. To sum up, a fossil is any remains of either an organism or its activities that is at least 10,000 years old.

Fossils are part of the cultural heritage of Uruguay and the whole world. According to the current laws in Uruguay they cannot belong to anyone in particular, for they are part of the country’s culture.

The extraction of fossilized remains can be a complicated task because these tend to be fragile and can easily break. Before removing a fossil from where it was found, the person doing so must collect data regarding its position and the sediment in which it is buried, and take photographs, since all this information is at times more important to understand the past than the fossil itself.


This group of giants that inhabited South America until not too long ago in geologic times, is the most spectacular mammalian fauna that ever lived anywhere in the world, with its unusual association of species weighing over a ton, that was Darwin’s first inspiration when developing his theory of evolution by natural selection. The animals considered in this group are not dinosaurs. The latter became extinct way before, 65 million years ago, while the megafauna became extinct only 10,000 years ago.

The South American Pleistocene megafauna is special from every point of view. First of all, it is comprised by many: 10 or 12 species of animals that weighed over one ton, living together. This is an example of the greatest diversity of giants ever known among mammals, and many of these species do not have living analogues. Among its members we can see the devastating saber-toothed tiger, a large-sized bear, a mastodon, several species of sloths weighing several tons, a giant armadillo and a few species of its relatives, the glyptodonts. The oddest animals among the megafauna are those that do not have living relatives: Toxodon and Macrauchenia. Both impress with their strange anatomy and their large size.
Ground sloths are relatives of the living sloths, those small mammals that hang from trees and sleep many hours a day. The most evident difference among them is their size, since ground sloths weighted over one ton, and therefore, did not rest on top of trees.
The glyptodonts are the giant relatives of armadillos. The scutes in their carapaces were made of bone with characteristic designs.

The megafauna became extinct around 10,000 years ago. Some of the proposed hypothesis regarding their disappearance are climate change and human impact, since our species coexisted with these giant animals for some time.

To learn more about the megafauna and paleontology, we recommend the books Megafauna: Giant Beasts of Pleistocene South America (in English), Hace sólo diez mil años (in Spanish) and Historia reciente del poblamiento remoto (in Spanish, free download).