A new giant carnivorous dinosaur with small arms like T. rex has been discovered

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Meraxes gigaslikewise a newly discovered dinosaur species with disproportionately short arms T. rex. Credit: Jorge A Gonzalez

Meraxes gigas — a new species of dinosaur with disproportionately short arms has also been discovered T. rex named Meraxes gigas.

Tyrannosaurs (as the famous T. rex) is not the only group of giant carnivorous dinosaurs with small arms. In fact, paleontologists have just discovered a new species of dinosaur with disproportionately short arms. T. rex named Meraxes gigas. The results were published in the journal Current Biology defended today (July 7). T. rex and M. gigas evolved to have short arms quite independently and identified several potential functions for short arms, such as mating or locomotion support.

“Fossil M. gigas It shows all regions of the skeleton, such as arms and legs, which help to understand some evolutionary trends and the anatomy of Carcharodontosaurids. M. gigas belongs,” says Juan Canale, project manager of the Ernesto Bachman Paleontological Museum in Neuquen, Argentina.

First, to set the record straight, the authors say this T. rex they didn’t get their short sleeves M. gigas or vice versa. Not only did it M. gigas became extinct about 20 million years ago T. rex became a species, but they are also very far apart in the evolutionary tree. “There is no direct connection between the two,” says Canale. Rather, Canale believes that having smaller arms somehow provided some sort of survival advantage for the two dinosaurs.


Meraxes gigas is a giant carnivorous dinosaur. Credit: Carlos Paplio

“I’m sure these proportionally small arms have some kind of function. The skeleton shows large muscle inserts and fully developed pectoral girdle, so the arm had strong muscles,” Canale said. This suggests that the arms did not shrink because they were unsuitable for dinosaurs. The more difficult question is what exactly the functions were.

From past studies, the research team found that dinosaurs liked it M. gigas and T. rex, the bigger their heads, the smaller their arms. Canale argues that they were not at all useful for hunting, as “actions related to predation were probably carried out by the head.”

“I tend to think their arms are used for other activities,” Canale says. From the fossil record, the team was able to paint a picture of its life M. gigas before dying. The dinosaur, which lived in the present-day northern Patagonia region of Argentina, was 45 years old, about 11 meters long, and weighed more than four tons. And he had a big family. “The group flourished shortly before extinction and reached a peak of diversity,” Canale said. “They used the arms for reproductive behavior, such as holding the female during mating or supporting themselves to stand up after a break or fall,” adds Canale.

A giant carnivorous dinosaur excavation site

excavation site Meraxes gigas. Credit: Juan I Canale

The group also found the skull M. gigas decorated with ridges, furrows, bumps and small horns. “These ornaments appear late in development when individuals become adults,” says Canale. The group believes these traits were likely used to attract potential mates. “Sexual selection is a powerful evolutionary force. But given that we can’t directly observe their behavior, it’s impossible to be sure,” says Canale.

“The fossil has a lot of new information, and it’s in great shape,” Canale says. He looks forward to exploring other questions M. gigas fossil can answer it. “We found the perfect location on the first day of the search and M. gigas found,” Canale says, “it was probably one of the highlights of my career.”

Reference: “A New Giant Carnivorous Dinosaur Reveals Convergent Evolutionary Trends in Theropod Arm Reduction” Juan I. Canale, Sebastián Apesteguía, Pablo A. Gallina, Jonathan Mitchell, Nathan D. Smith, Thomas M. Cullen, Alejan Feder Halen, Alejan Shinyauz, Alejan By Shinyauz A. Gianechini, Peter J. Makovicky, July 7, 2022, Current Biology.
DOI: 10.1016/j.cub.2022.05.057

This work was supported by the US National Science Foundation and the National Geographic Society.

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