Meraxes Gigas: Giant New Carnivorous Dinosaur Discovered With Tiny Arms Like T. rex

Meraxes Close Up

Meraxes gigas, a newly discovered species of dinosaur with disproportionally short arms just like T. rex. Credit: Jorge A Gonzalez

Meraxes gigas — a new species of dinosaur has been discovered with disproportionally short arms just like T. rex called the Meraxes gigas.

Tyrannosaurs (like the infamous T. rex) is not the only group of gigantic carnivorous dinosaur with tiny arms. In fact, paleontologists have just discovered a new species of dinosaur with disproportionally short arms just like T. rex called the Meraxes gigas. The findings, published in the journal Current Biology today (July 7), argued that T. rex and M. gigas evolved to have tiny arms completely independently, and identified several potential functions for the short arms such as mating or movement support.

“The fossil of M. gigas shows never seen before, complete regions of the skeleton, like the arms and legs that helped us to understand some evolutionary trends and the anatomy of Carcharodontosaurids – the group that M. gigas belongs to,” says Juan Canale, the project leader at Ernesto Bachmann Paleontological Museum in Neuquén, Argentina.

First, to set the record straight, the authors say that T. rex did not get their short arms from M. gigas or vice versa. Not only did M. gigas become extinct almost 20 million years before T. rex became a species, but on the evolutionary tree, they are also very far apart. “There is no direct relationship between both,” says Canale. Rather, Canale believes that having tiny arms somehow provided the two dinosaurs some kind of survival advantage.


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

“I’m convinced that those proportionally tiny arms had some sort of function. The skeleton shows large muscle insertions and fully developed pectoral girdles, so the arm had strong muscles,” says Canale. This shows that the arms did not shrink because they were useless to the dinosaurs. The more difficult question is what exactly the functions were.

From past studies, the research group established that for dinosaurs like M. gigas and T. rex, the larger their heads were, the smaller their arms became. They were definitely not useful for hunting, as “actions related to predation were most likely performed by the head,” Canale argues.

“I’m inclined to think their arms were used in other kinds of activities,” says Canale. From the fossil record, the team was able to paint a picture of the life of this M. gigas before it died. Living in the present-day northern Patagonia region of Argentina, the dinosaur was 45 years old, about 11 meters long, and weighed more than four tons. And, it had a big family. “The group flourished and reached a peak of diversity shortly before became extinct,” says Canale. “They may have used the arms for reproductive behavior such as holding the female during mating or support themselves to stand back up after a break or a fall,” Canale adds.

Giant Carnivorous Dinosaur Excavation Site

Excavation site of Meraxes gigas. Credit: Juan I Canale

The team also found that the skull of M. gigas was decorated with crests, furrows, bumps, and small hornlets. “Those ornamentations appear late in the development when the individuals became adults,” Canale says. The group thinks that the features were probably used to attract potential mates. “Sexual selection is a powerful evolutionary force. But given that we cannot directly observe their behavior, it is impossible to be certain about this,” says Canale.

“The fossil has a lot of novel information, and it is in superb shape,” says Canale. He looks forward to exploring other questions that the M. gigas fossil can help him answer. “We found the perfect spot on the first day of searching, and M. gigas was found,” Canale says, “It was probably one of the most exciting points of my career.”

Reference: “New giant carnivorous dinosaur reveals convergent evolutionary trends in theropod arm reduction” by Juan I. Canale, Sebastián Apesteguía, Pablo A. Gallina, Jonathan Mitchell, Nathan D. Smith, Thomas M. Cullen, Akiko Shinya, Alejandro Haluza, Federico A. Gianechini, Peter J. Makovicky, 7 July 2022, Current Biology.
DOI: 10.1016/j.cub.2022.05.057

This work was supported by The National Science Foundation of the United States and the National Geographic Society.

10 Comments on "Meraxes Gigas: Giant New Carnivorous Dinosaur Discovered With Tiny Arms Like T. rex"

  1. NOT QUITE as awe-inspiring as Miraxes gigas but the lowly Raccoon has a methodology for dealing with hunting dogs. In kind to Meraxes, the Raccoon has relatively short forelegs (with very sharp claws), compared to its hind quarters; resulting in a butt-high stance. Pity the dawg that tries to roll that ‘Coon over, to get to his underbelly. The Raccoon will comply, and when the hapless dog rolls him over for the killing choke-hold on the throat and straddles his quarry, or attacks back-to-front for a shot at the the genitals (better), the “overmatched” Raccoon will rip the offending party’s belly wide open, back-to-front, with its fore-claws,with rear claws assisting. GRUESOME. Been there. Saw that, in the Southern hills of PA.
    For this reason, ‘Coon Hounds are trained against closing for a kill. They are trained to trap and isolate their quarry, in their number, and Bay like all Hell. Usually three and sometimes four.
    I presume that Miraxes preyed on much larger Herbivores. Getting under their prey and “gutting” it seems a much swifter approach to killing than jumping on its back; although, if Meraxes was a pack hunter, its compatriots probably assisted with the direct attack to legs, tail and throat. First rule of predation: Work together. Multiple assaults. Minimize damage to oneself. Nature is one unforgiving Mistress for the injured, incompetent or terminally slow by design.
    BTW: There is SOME evidence that Neanderthal hunted MUCH larger Mastodon/Mammoth prey by a similar methodology, with the added twist of insight “embodied” in spooking their wounded quarry over a cliff.

  2. Snowball Solar System | July 8, 2022 at 5:42 am | Reply

    Where did I read just recently that T. rex arms evolved to be short to avoid accidental predation by competitors at carcasses?

  3. Mark Smallcombe | July 9, 2022 at 4:45 am | Reply

    Why don’t they show you the actual “fossilized body?” A lot of the drawings are figments of people’s imagination and a lot of it is a scam

  4. Carcharodontosauridae is a tyrannosaur fuse frontal that a mesoeucrocodylia feature it’s not a allosaurus it’s fuse frontal not as fuse as spinosauridae .clearly they use arm quadrupedal as to launch bipedal to get some speed all theropod did that . that why they have furcula a flight feature that why gator have well develope pectoral girdle in the gator it was before eusuchian monster speedy centra vertebrae joint .but theropod was a poor quadrupedal with bad arm movement and fuse ankle it only use it for launch .finger are the same i here nothing about that .compsognathus a tyrannosaur the second finger is same size as the first finger it was not a grasping predator .most theropod were grasping predator because of weak bite force they lack a full palate like mammal t.rex gator spinosaurus .dinosaur are transition animal that turn into super dinosaur the gator .the bite force that can crush metal.gator arm are a bird flight feature so the arm do not break because it was fast .theropod were fast .theropod were crouching predator like most predator today .and carcharodontosauridae has other tyrannosaur feature.theropod finger only change when they become a head killer .that why t.rex only has 2 finger it was fast quadrupedal .gator still has grasping big thumb claw a dinosaur grasping feature I am really surprise it still there so dinosaur finger is the success for the gator.but because gator is doing a lot of quadrupedal the first finger is reduce a quadrupedal feature but it is still bipedal like it’s ancestor spinosauridae .but spinosauridae is a primitive theropod like t.rex that could not sprawl .allthou theropod was a joke quadrupedal it is still a quadrupedal.gator is human ankle bipedal. t.rex walk on there toes like most mammal.human do not walk on there toes .so they develope a speedy human ankle very rare ankle in the animal kingdom only 2 reptile it is found a bipedal feature allso found in one mammal human because they are bipedal .mesoeucrocodylia allso has true vomer a mammal feature maybe birds too only whale mesoeucrocodylia has it they allso has same bone fuse like birds to make a beak only whale once.the reason why dinosaur rarely change there finger because they need it to grasp that why most predator theropod look like that.

  5. Isn’t that just convenient that on the FIRST day of their search, they “FIND” this. Remember the kid that found a fossil and it was later revealed that he was told to go to a spot and dig… all of this dinosaur talk is to further their narrative that we don’t have a God and that we had this meteor that hit our planet causing extinction. None of that is true. We live on a flat plane, not a planet. the craters were the deep oceans opening up and causing our great flood. NASA is a hoax. it all is. they lie about everything…

  6. Fossil crates YouTube has answer about the finger the science report. The claws were reduce it was a head killer .tyrannosaur like mega raptor have big claws .like t.rex finger it had primitive finger movement it was not like allosaurus even more evolution on megaraptor finger grasping evolution keep evolving with the bad finger that why they have big claws .interesting 2 tail bone is fuse fusion of vertebra is rare only see that in birds centra vertebrae joint .synsacrum fusion in the mesoeucrocodylia notosuchus number 2 sacral and number 3 .6 in the dinosaur carnotaurus .by this finding meraxes Gigas is a tyrannosaur by notosuchus linking .meraxes allso is a tetanuran like the gator.dinosaur arm are very robust birds are not .very slim arms but arms of bird are strong it has to be it’s a flying animal.reason for robust dinosaur arm because dinosaur were fast animal it’s to prevent violent force that can break the arm.meraxes was a leg grasping another fail evolution this is because of weak bite force like grasping dinosaur. Turtle allso use there legs a crocodilian type of animal because of the skin turtle are not thecodont.

  7. Meraxes is a deinocheirus they are tyrannosaur they have fuse tail fuse vertebrae .deinocheirus finger about same size that very different from other tetanuran allso has duck face like mesoeucrocodylia anatosuchus duckcroc. deinocheirus is a carcharodontosauridae these carcharodontosaurus were head killer .allosaurus has fuse parietal like acrocanthosaurus spinosauridae t.rex carcharodontosaurus allso fuse to frontal but frontal of allosaurus is not fuse .so tyrannosaur feature is fuse frontal .t.rex parietal allso fuse to frontal highly mesoeucrocodylia feature.I can not believe allosaurus has fuse parietal I thought much more primitive than that.protosuchus lack fuse parietal .in protosuchus type of dinosaur erpetosuchus allso has fuse parietal .deinocheirus finger is not of grasping predator is for speedy quadrupedal .carcharodontosaurus is a tyrannosaur like compsognathus they lack a sagittal crest the good fossil of scipionyx they found no sagittal crest at all. Acrocanthosaurus frontal is well fuse not like carcharodontosauridae .I saw on YouTube they show how carcharodontosaur is a tyrannosaur they did not know it was evidence but I do know.

  8. I believe scientists have only found 2 complete dinosaurs. Intact.. I don’t know. This is very fascinating. He looks put together like a puzzle. How many dinosaurs were found intact? Great article.

  9. Remember Lucy? From 1 tooth they rebuilt Lucy. Turned out it was the tooth of a prehistoric pig!

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