At the time, the area was hot and humid with plenty of waterways and vegetation, including large trees, Juan Canal, project leader for the Ernesto Bachmann Museum of Paleontology in Neuquen, Argentina, told CNN.
This carnivorous animal is from the Carcharodontosauridae group of dinosaurs, which lived in the Cretaceous period, 145 to 66 million years ago, according to the study.
A group of Carcharodontosauridae fossils have been found in the past 30 years, but little is known about their skulls, forearms or feet.
That changed with the discovery of M. gigas, thanks to the remarkably complete fossil.
“For the first time, we know, in great detail, certain parts of the anatomy of these giant carnivorous dinosaurs,” Kanal said.
The researchers found an almost complete forelimb, leading them to conclude that M. gigas had arms as small as this large dinosaur, a physical feature that has puzzled paleontologists for a long time.
They also found a nearly complete skull and foot, Kanal said, which helped shed light on how this group of dinosaurs evolved, explaining that there was a trend toward larger body sizes, larger skulls and smaller arms relative to the body.
‘There was some kind of arms race’
The fossil was found in the Huencol Formation, where the study said the remains of one of the largest known land animals of all time, Argentinosaurus huencolensis, were found from the same time period as the M. gigas fossil.
The area is also known to be home to other carnivores, albeit smaller than the M. gigas dinosaurs, as well as other types of long-necked herbivores.
It’s very difficult to determine what dinosaurs ate, Kanal said, but loose teeth have been found at excavation sites where the fossils of herbivorous dinosaurs were discovered along with the carnivorous dinosaurs.
This, he added, means that we can say that M. gigas would have preyed, at least in part, on these long-necked herbivores such as Argentinosaurus huinculensis.
“It’s no coincidence that giant herbivorous dinosaurs and giant carnivorous dinosaurs lived in the same environment,” Kanal said, explaining that while herbivores evolved larger bodies as a form of defense, carnivores also hunted.
“There was some kind of arms race,” he said.
“No direct relationship” with T. rex
But the team says that M. gigas evolved separately into T. rex and became extinct about 20 million years before T. rex walked on Earth.
Kanal said that while both dinosaurs had large heads and small arms, their skeletons were very different.
“There is no direct relationship,” the channel said.
Kanal said that the ancestors of M. gigas had longer arms and smaller heads and that their arms were important in hunting, but this has changed over time.
Previous research found that dinosaur species such as M. gigas and T. rex developed smaller arms the larger their heads.
Canal said this indicates that the weapons were not used for hunting, but instead used their heads to kill their prey.
“What I believe is that in more advanced forms…the activities associated with predation, such as catching or carrying prey, could have been done directly with the head,” he said.
However, the fossil shows that although the arms were short, they were muscular and the pectorals were well developed, Kanall said.
“This is not equivalent to a limb that has no function,” he said, adding that it could be used to lift off the ground, or as a support for the female during mating. Researchers do not know whether this fossil belonged to a male or a female dinosaur.
The team also found that M. gigas had decorations such as crests, grooves, thorns and tiny cloves on its skull, which were likely used to attract potential mates.
Kanal said there is still more work to be done on M. gigas, and his colleague at the museum is writing a letter on his feet and arms.
In addition, there are plenty of fossils yet to be discovered in the area, as well as dinosaur footprints for analysis, he said.
“We have a lot of work to do,” Kanal added.
