Newly Discovered Dinosaur Shows Pattern of Huge Animals with Small Arms

Close your eyes and imagine Tyrannosaurus Rex. Can you see his huge head, sharp teeth, and thin arms?

The predator of the late Cretaceous in the northern hemisphere wasn’t the only dinosaur to have this strange body type. So did aplesauruses in the southern hemisphere, such as Carnotaurus. So did carcharodontosaurid Miraxis Gegasalso from the southern half of the world but approximately 20 million years ago, during the early Cretaceous period.

M. gigas is a newly discovered species in Patagonia, Argentina. Peter Makovicky of the University of Minnesota was one of the team of paleontologists that excavated it. (Palaeontologists are scientists who study ancient life.) Finding M. gigas, Makovicki says, made him and other researchers think about what carnivorous theropods have in common and why.

He says, they all had “really short arms and really huge skulls.” M. gigas weighed about 4 tons, and T. rex And the weight of Carcharodontosaurus is about 7 to 8 tons. Their heads grew to about 4 or 5 feet, and their arms were nearly the length of an adult human.

“The fact that these breeds are so similar in their body outline seemed like it couldn’t have been a coincidence,” Makovicki says.

In the past, many researchers focused on what theropods’ small arms use. Makovicki says M. gigas shows that while their arms may have had purposes as they evolved to get smaller and smaller, such as helping dinosaurs to lie on their stomachs, it is possible that they became less important—at least in catching prey.

These different theropod lineages evolved over millions of years, and on different continents, “to look like this for a reason, and something about that [theropod] body plan [means] “As their skulls get disproportionately larger, their arms get disproportionately shorter and they transfer any predatory function of the forelimbs to the head,” says Makovsky.

Patagonia has always been a dinosaur hot spot, not only for giant theropods but also for rare small fossils and dinosaur tracks. Makovicki and his team found not only M. gigas but at least two other Serbian fossils at a site in the Neuquén Basin. “You just had this huge pile of bones that the more you keep digging, the more bones will come out,” he says. “At some point, our meat-eating dinosaur started bumping into the skeleton of a large sauropod, so it became more like a little chopsticks game.”

Adding to the challenge was figuring out how to dig things upside down. Makovicki says, “Some of the bones had stuck to the bedrock at the top and formed a ledge. You had to actually crawl down and figure out a way to get the bones out of the roof of such a small space, which you don’t usually do. You usually dig down and lift.”

Some of these discoveries have yet to be studied and described, and there may be more new species in the mix. But Makovsky says he wants to investigate further into the theropod’s arms. “The arm’s length is not less than a certain percentage. Why is that?” Asked.

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