At 11 meters long and over four tons, a new species of carnivorous dinosaur discovered in Argentina seems to be cut out to play a prominent role in humanity’s nightmares, even earning the name of one of the most fearsome dragons in the “Game of Thrones” series. Only one thing stands out in this scenario: the tiny front legs of the animal.
At first glance, the disproportion in the limbs seems even ridiculous, but the analysis of the species named as Meraxes gigas brings important information to understand how the animal and so many other great predators of the Age of Dinosaurs ended up developing little arms of this type over millions of years.
This is what the paleontologists who discovered and analyzed the fossils argue, in an article that has just appeared in the specialized journal Current Biology. The team of scientists is coordinated by Juan Canale, from the National University of Rio Negro, and includes the participation of other paleontologists from Argentina and the USA.
Luckily for the researchers, the M. gigas It is the animal with the most complete preservation of its front legs among the members of its group, that of the carcharodontosaurids, which includes a series of other large South American predators, present even in Brazil.
The fossils, which still include an almost complete skull (no jaw), bones of the chest and pelvis and vertebrae of the neck, back and tail, were found in the Neuquén region of northern Patagonia, and have about 90 million of years old. It was already known that the short arms were a hallmark of the group, but this is the first time that such complete data on the limbs can be obtained from the fossil record.
The first thing that becomes clear based on this new information is that the little arms were not a simple anatomical “leftover”, something that the animal apparently no longer used. “I’m convinced they played some sort of role,” Canale said in an official statement. “The skeleton shows that they had large muscle attachments and shoulder girdles. [a região das clavÃculas] fully developed. That is, the arms had strong muscles.”
If that was the case, what would explain the diminutive size? The experts’ main hypothesis has to do with the way in which the anatomical structure of animals developed. It turns out that the mini-arm phenomenon is something that appears repeatedly, independently, in several other lineages of carnivorous dinosaurs that reached sizes around 10 m in length or more and favored the development of huge heads with powerful jaws.
The most famous case, also ridiculed because of his little arms, is that of the famous tyrannosaurusrexactually a very distant relative of the Meraxes gigas —the animals reached their anatomical pattern in a parallel way, since the T. rex lived 20 million years later. Another important fact: the small arms seem to have maintained a very similar proportion in all groups of large carnivorous dinosaurs, in general with about 50% of the size of the animals’ femur.
This led the authors of the new study to propose that there must have been a kind of coupling in the development of the animals’ muscles and skeleton, probably of genetic origin, in which the formation of the enormous heads and jaws was correlated with a proportional decrease in the legs of the animal. front. It sounds strange, but similar things happen in other groups of animals.
Even if the idea is confirmed, the mystery about the usefulness of the little arms after this evolutionary process still remains. Canale has some ideas. “They may have used their arms for reproductive behaviors, holding the female in copulation, or for support after a fall,” he says.
