They discover in Argentina a new species of dinosaur with small arms like T. rex

() — Paleontologists from Argentina discovered a new species of dinosaur with disproportionately short arms like those of Tyrannosaurus rex.

A fossil of Meraxes gigas, as the new dinosaur has been named, was found in what is now the northern Patagonia region of Argentina, revealing the creature was 11 meters long and weighed more than four tons, according to a published study. in academic journal Current Biology this Thursday.

At that time, the area would have been hot and humid, with many canals and vegetation, including large trees, Juan Canale, project director at the Ernesto Bachmann Paleontological Museum in Neuquén, Argentina, told .

The carnivore belongs to the Carcharodontosauridae group of dinosaurs, which lived in the Cretaceous period, 145 to 66 million years ago, according to the study.

Numerous fossils of Carcharodontosauridae have been found in the last 30 years, but little was known about their skull, forearms, or feet.

This has changed with the discovery of M. gigas, thanks to the extraordinarily complete fossil.

Artist’s reconstruction of the possible appearance of Meraxes gigas.

“For the first time we know, in great detail, certain parts of the anatomy of these gigantic carnivorous dinosaurs,” said Canale.

The researchers found a nearly complete forelimb, allowing them to conclude that M. gigas had tiny arms for such a large dinosaur, a physical feature shared with T. rex that has long baffled paleontologists.

They also found a nearly complete skull and foot, allowing them to shed light on how this group of dinosaurs evolved, Canale said, explaining that there was a trend toward larger body sizes, larger skulls and smaller arms in proportion to the body. .

There was a kind of “arms race”

The fossil was found in the Huincul Formation, where, according to the study, remains of one of the largest known land animals of all time, Argentinosaurus huinculensis, dating from the same period as the M. gigas fossil, have been found.

The area is also known to have harbored other carnivorous dinosaurs, albeit smaller than M. gigas, as well as other species of long-necked herbivores.

Canale said that, in general, it is very difficult to establish what the dinosaurs ate, but the loose teeth found in the excavations in which fossils of herbivorous dinosaurs have been discovered correspond to carnivorous dinosaurs.

This means that we can say that M. gigas would have predated, at least in part, these long-necked herbivores such as Argentinosaurus huinculensis, he added.

“It’s not a coincidence that giant herbivorous dinosaurs and giant carnivorous dinosaurs lived in the same environments,” Canale said, explaining that as herbivores evolved larger bodies as a form of defense, carnivores also evolved to be able to prey on them.

“There was a kind of arms race,” he said.

No direct relation to T. rex

But the team claims that M. gigas evolved separately from T. rex and went extinct nearly 20 million years before T. rex walked the Earth.

Canale said that although the two dinosaurs had large heads and small arms, their bone structure is very different.

“There is no direct relationship,” Canale said.

The ancestors of M. gigas had longer arms and smaller heads, and their arms would have been important for hunting, Canale said, but this changed over time.

Previous research found that dinosaur species such as M. gigas and T. rex developed smaller arms as their heads grew larger.

This shows that the arms were not used for hunting, and instead used the head to kill prey, Canale said.

“What I think is that, in the most evolved forms … activities related to predation, like grabbing or holding prey, would have been done directly with the head,” he said.

However, the fossil shows that although the arms were short, they were muscular, and the chest muscles were also well developed, Canale said.

“This is not consistent with a limb that has no function,” he said, adding that they could have been used to help get up from the ground, or to support the female in mating. The researchers don’t know if this fossil belonged to a male or female dinosaur.

The team also found that M. gigas had ornamentation such as ridges, grooves, bumps, and small horns on its skull, which were likely used to attract potential mates.

More work still needs to be done on M. gigas, Canale said, and a colleague at the museum is writing a thesis on its feet and arms.

In addition, there are plenty of fossils that have yet to be excavated in the area, as well as dinosaur footprints to analyze, he said.

“We have a lot of work ahead of us,” added Canale.