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They describe a species of dinosaur discovered in Argentina that sheds new light on the tiny arms of tyrannosaurs


Although it was not the largest of its family, the ‘Meraxes gigas’ measured about 11 meters from the snout to the tip of the the tail and weighed more than 4,000 kilos.

A group of Argentine, American and Canadian paleontologists released this Thursday a new species of dinosaur, named ‘Meraxes gigas’. Its remains were found in 2012 in the province of Neuquén, Argentina, but its full description was only recently published in the journal Current Biology.

The predator, which is part of the ‘Carcharodontosauridae’ family, a group of giant carnivorous theropods, provides clues to the evolution and biology of several closely related species, including tyrannosaurs. In particular, it helps to understand why these animals had such large skulls and small arms.

Although not the largest of the carcharodontosaurids, ‘Meraxes gigas’ measured around 11 meters from the snout to the tip of the tail and weighed more than 4,000 kilos. The fossils were recovered from rocks that are between 90 and 95 million years old, the researchers detail.

“The discovery of this new carcharodontosaurid, the most completed so far, it gives us an exceptional opportunity like never before to learn about its systematics and paleobiology and its real size”, said a co-author of the study, Sebastián Apesteguía, from the Maimonides University of Argentina, quoted by EurekAlert.

As for the possible uses of the tiny forelimbs of tyrannosaurs and species similar to them, scientists have always debated various hypotheses.

“We should not worry so much about the use of the arms, because in reality the arms are reduced as a consequence of which the skulls become massive,” said Peter Makovicky of the University of Minnesota. “Whatever the use of the arms, they are taking on a secondary function, as the skull is being optimized to handle larger prey”, concluded the researcher.

“Everything that any carnivorous hunting animal could have done with its arms, it would have done with its head: grab the prey, manipulate it, hold it against the ground, kill it,” explains Juan Ignacio Canale, from the National University of Río Negro (Argentina), quoted by El País.

The team also noted that ” the reduction of the arms was progressive , until it represented a proportion of 40% of the size of the femur”. Then it stopped for an unknown reason, although the authors tested some hypotheses.

“We observed that the pectoral girdle […], the scapula and other bones, are not reduced together with the arm, but it is a very large and developed bone, in which a lot of musculature that goes to the extremity fits”, the paleontologists affirmed. “So there is a limit to which it can be reduced, because that muscle has to be inserted somewhere. We believe that the limit has to do with that ,” the scientists explained.


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