New dinosaur species discovered that had tiny arms like T. rex

A fossil of Meraxes gigas, as the new dinosaur was called, was found in what is now Argentina’s northern region of Patagonia, revealing that the creature was 11 meters (36 feet) long and weighed more than four tons, according to a study published Thursday in the journal Current Biology.

At that time, the area would have been hot and humid, with lots of waterways and vegetation, including large trees, Juan Canale, the project manager for Ernesto Bachmann’s Paleontological Museum in Neuquén, Argentina, told CNN.

The carnivore is from the Carcharodontosauridae group of dinosaurs, which the study says lived in the Cretaceous Period, 145 to 66 million years ago.

A fair number of Carcharodontosauridae fossils have been found in the past 30 years, but little was known about their skulls, forearms, or feet.

That all changed with the discovery of M. gigas thanks to the remarkably complete fossil.

An artistic reconstruction of what Meraxes Gigas may have looked like.

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

The researchers found an almost complete front leg, allowing them to conclude that M. gigas had tiny arms for such a large dinosaur, a physical trait it shares with T. rex and that has long puzzled paleontologists.

They also found an almost complete skull and foot, which allowed them to shed light on the evolution of this group of dinosaurs, Canale said, explaining that there was a trend toward larger body sizes, larger skulls, and smaller arms relative to the body.

“There was a kind of arms race”

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

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

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Canale said that it’s generally very difficult to determine what dinosaurs ate, but loose teeth found at dig sites where fossils of herbivorous dinosaurs have been uncovered have been matched to carnivorous dinosaurs.

This means we can say that M. gigas would have at least partially preyed on these long-necked herbivores like Argentinosaurus huinculensis, he added.

“It’s no coincidence that giant herbivorous dinosaurs and giant carnivorous dinosaurs lived in the same environment,” said Canale, who explained that carnivores did the same when herbivores evolved larger bodies as a form of defense to be able to hunt them.

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

‘No direct relation’ to T. rex

But the team says M. gigas evolved separately from T. rex and became extinct nearly 20 million years before T. rex lived on Earth.

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

“There is no direct relationship,” Canale said.

M. gigas’ ancestors had longer arms and smaller heads, and their arms would have been important when hunting, Canale said, but that changed over time.

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

This shows that the arms weren’t used for hunting, but that they used their heads to kill their prey, Canale said.

“What I think is that in the more evolved forms … predator-related activities, like grasping or holding the prey, would have been done with the head immediately,” he said.

However, the fossil shows that the arms, while short, were muscular and the pectorals were also well developed, Canale said.

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

The team also found that M. gigas had adornments such as crests, furrows, bumps and small hornets on its skull, which were likely used to attract potential mates.

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

In addition, there are many fossils in the area that have yet to be excavated, as well as dinosaur footprints that need to be analyzed, he said.

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