Justice for T. Rex: Scientists Discover Another Giant Dinosaur With Tiny Arms

What is happening

In Argentina, a team of scientists excavated the fossil of a dinosaur with arms comparable to miniature T. rex limbs.

why is it important

This adds evidence to the theory that the mini-dinosaurs’ limbs weren’t useless. They may have had some sort of evolutionary advantage.

Despite its colossal skull, imposing size, and carnivorous appetite, Tyrannosaurus rex has the unfortunate honor of being a punchline due to a hard-to-miss quirk. “Catch me if you can with your silly little arms, T. rex,” says a 10-year-old watching a dinosaur documentary somewhere, probably.

But thanks to new research published Thursday in the journal Current Biology, we may finally have justice for the T. rex’s tiny arms. Not only have scientists excavated the fossil of another massive meat-eating dinosaur with mini upper limbs – called Meraxes gigas – but they also consider it proof that small dinosaur arms actually had an advantage of important survival a long time ago.

The team holding a white plaster jacket, with part of the complete fossil inside.

The survey team transports the fossil in a plaster casing.


“I am convinced that these proportionately tiny arms had some sort of function,” Juan Canale, project manager at the Ernesto Bachmann Paleontological Museum in Argentina, said in a statement. “The skeleton shows large muscle insertions and fully developed pectoral girdles, so that the [arms] had strong muscles. This means that the arms did not shrink because they were useless for the dinosaurs.”

However, as Canale puts it, “the more difficult question is what exactly were the functions”.

New dino specs

After analyzing the new fossil, located in the present-day northern region of Patagonia at the southern tip of South America, the recovery team concocted a visual image of what M. gigas might have looked like there. billions of years old. “The fossil contains a lot of new information and is in superb condition,” Canale said.

To name just a few of its features, this huge dinosaur was probably about 45 years old when it died, was about 11 meters (36 feet) long and weighed over 4 tons. And it had a rather majestic facade.

An artist's illustration of the head of M. gigas, furrow ridges and indentations seen.

This is what Mr. gigas’ head probably looked like.

Jorge A. González

The researchers found fossilized evidence that this iteration of M. gigas contained a skull decorated with ridges, furrows, bumps and small hornets, which Canale says appeared during adolescence and once solidified. become an adult. It is possible that these brands were used to attract potential partners.

“Sexual selection is a powerful evolutionary force,” Canale said. “But since we can’t directly observe their behavior, it’s impossible to be certain.”

A dusty Argentinian dig site.

The dig site in Argentina where Mr. Gigas’ fossil was found.

Juan I. Canale

All things considered, M. gigas looks a bit like T. rex, even though it descends from an entirely separate dinosaur classification called – get ready for a bite – Carcharodontosauridae. And that brings us to perhaps the most striking part of the team’s discovery.

M. gigas and T. rex have never, ever interacted with each other. We can be sure because Mr. gigas has disappeared 20 million years even before T. rex walked on Earth.

Thus, the two dinos must have developed their unique limbs independently, which underscores the theory that their miniature arms had a special purpose. Evolutionary advantages tend to appear at different times in history because they have advantages that permeate species across time frames.

Although still speculative, some ideas Canale has for the reduced arm trait are that these dinosaurs “may have used the arms for reproductive behavior, such as holding the female during mating, or [to] supporting themselves to get back up after a break or a fall.” In other words, it may have been easier for T. rex or M. gigas to hug their companions with a small upper frame or quickly push themselves from the soil after face planting.

For strategic moves, bigger is not always better.

In the future, researchers hope to continue studying the skeleton of M. gigas to get to the bottom of the small arms saga. And even further, the fossil could help solve many other outstanding paleontological mysteries. “We found the perfect spot on the first day of the search, and Mr. gigas was found,” Canale said. “It was probably one of the most exciting moments of my career.”

Elna M. Lemons