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In the footsteps of the terrible reptiles that reigned before the dinosaurs

2020-11-10T18:03:12.240Z


A group of paleontologists finds hundreds of fossilized footprints in southern Bolivia, the oldest in the country, produced 235 million years ago by huge reptile terrestrial relatives of crocodiles


They are not ten.

Not fifty.

Rather, they are hundreds of fossilized footprints.

"It is impossible to evaluate their quantity", assures Sebastián Apesteguía.

More than ten years ago, this Argentine paleontologist arrived at the Tunasniyoj and Ruditayoj mega-site, accompanied by his colleague Pablo Gallina.

There, amidst the silence and oppressive heat of southern Bolivia, the researchers found a true treasure at their feet: a minefield mined by superbly preserved fossil tracks of animals from the past.

Bolivia is one of the countries with the greatest variety and quantity of footprints of this type in the world with sites like Cal Orcko, declared a national Natural Paleontological Monument in 1998. "All the other footprints found in the country correspond to the Upper Cretaceous," says Apesteguía , researcher at the Azara Foundation / Maimónides University.

"They are 'only' 70 million years old."

Therefore, at the time, scientists considered in a 2011 study that these traces made by quadruped animals had been left by the last dinosaurs.

Only in time would they realize how wrong they were.

In 2018, Apesteguía returned with a larger team of researchers to the area - a valley near the town of Icla, 100 km southeast of Sucre - to re-analyze those sandstone slabs covered with footprints.

Geological and palaeoenvironmental studies carried out at the site changed what they thought: they revealed that the tracks were actually much older.

“They belong to the middle of the Triassic period, that is, 235 million years ago.

Their producers would not have been dinosaurs but the predators that preceded them ”, Apesteguía points out in an article published a few days ago in the

Historical Biology

magazine

.

"The tracks were left by huge animals distantly related to today's crocodiles: the rauisuquios."

Dinosaur Eaters

More than 230 million years ago, when today's continents were packed into a single supercontinent called "Pangea" - which means in Greek "the whole Earth" and was named for the German geophysicist Alfred Wegener in 1915 - dinosaurs were small. and elusive and just appeared to the world.

At that time, the kings were different: the rauisuchios, huge reptiles terrestrial relatives of crocodiles, between 3 and 10 meters long.

"They dominated the planet for 80 million years," says Apesteguía, a researcher at Conicet.

"Between 280 and 200 million years ago."

Fossil remains of the rauisuchios were found in various parts of the world, but especially in South America.

For example, in Ischigualasto (or the "Valley of the Moon") in the Argentine province of San Juan.

Colossal animals such as

Saurosuchus galilei

or

Fasolasuchus

lived there

.

In the world these creatures lived in, deserts predominated.

The flowers did not yet exist, but there were ferns with seeds, which were spread over all the continents.

Being reptiles, rauisuchios could live in these very arid and water-scarce environments.

With far less marketing than T. rex, these huge-skull animals full of curved, jagged teeth were just as terrifying, or more terrifying: They fed on the earliest herbivorous dinosaurs, as well as the distant relatives of mammals, the cynodonts.

Until one day they disappeared.

“The causes of the extinction of these animals are not well known.

It has not been one of the greatest extinctions but it was important enough to wipe out the main predators in the Jurassic. "

This paved the way for dinosaurs to become the dominant large land animals.

In addition to their bones, claws and teeth, the Rauisuquios left behind countless traces, traces of their former presence, like these impressions in the Bolivian department of Chuquisaca.

"The fossilized footprints of these vertebrates allow us to 'see' extinct animals in motion, providing valuable information on different aspects of behavior and ecology," indicates the ichnologist Paolo Citton, from the National University's Paleobiology and Geology Research Institute. of Río Negro of Argentina.

"I was surprised by the amount of footprints preserved at these sites left by different individuals."

If paleontology is detective enough, ichnologists are the Sherlock Holmes of this science.

They follow trails and reconstruct what prehistoric animals looked like, moved and interacted without digging up a bone.

These specialists work with all kinds of vestiges or traces, that is, any indication of the biological activity of a living being: from footprints to fossil excrement (or coprolites).

“We looked at the rakes and then we took several steps to get information about the growers and the anatomy of the legs,” says Citton.

“We literally threw ourselves on the floor and drew everything.

We were lucky enough to be able to work with quite informative traces: we obtained information for example on the number and orientation of the fingers and claws, on how these animals supported their legs during locomotion, and if they were bipeds or quadrupeds ”.

Seen in this way, the fossilized tracks function like photographs in time: they tell about a great variety of animal behaviors from the past at a particular moment.

They report on the presence of ancient creatures in a certain place and what they were doing in the environment in which they lived.

Reptile roads

The new dating makes these remains the oldest land animal tracks in Bolivia.

Hundreds of isolated tracks can be seen at the site, but in some cases others of animals walking together are observed.

Using digital techniques, the group's ichnologists made three-dimensional models of the impressions and of the entire surface.

"There are traces of an adult accompanied by footprints of the same type, but much smaller," says Apesteguía.

"This makes us think that he was accompanied by his young."

In other areas, the five-toed prints accumulate: it could be traces of groupings of animals in an oasis.

"This finding is quite special because this type of footprints do not usually appear in such numbers," warns the ichnologist Silvina de Valais, a researcher at the National University of Río Negro, in the Argentine city of General Roca.

“For better communication, we ichnologists name the footprints.

This type of footprints are called

Brachychirotherium

or brachyquiroterides ”.

The variety of the traces led scientists to think that they would have been left behind not only by rauisuchians but also by other contemporary animals: armored herbivorous reptiles called aetosaurs.

"These species used to move more in groups than the predators, usually more solitary," says Apesteguía.

"In both cases, they are several species of animals that vary between three and seven meters in length."

The researchers think that the terrain these animals walked on in the sands of what was more than 230 million years ago the Central Pangea Desert was wet.

At some point, it dried slightly and decanted very fine sediment that fixed the tracks.

Erosion did its job for millions of years and helped keep them intact to this day.

"We still have several questions," warns de Valais.

“Did they move in packs?

Did they migrate?

Did they come and go in the same places, perhaps year after year?

They are very interesting questions that will guide future work for years ”.

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Source: elparis

All news articles on 2020-11-10

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