New Dinosaur Discovery Provides Insight Into The Short Arms Of Prehistoric Carnivores

While the meat-eating dinosaur Meraxes gigas was initially discovered in 2012, some interesting discoveries have recently come to light. Members of the University of Minnesota have been hard at work researching the carnivore’s remains. It appears that they may have a new idea on why giant meat lovers from the past developed short arms.

The study not only sheds light on Meraxes gigas, but also on some of its popular cousins such as Tyrannosaurus rex and Giganotosaurus. Let’s take a closer look at what these scientists discovered, and we’ll share some more details on this intriguing prehistoric carnivore.

Meet Meraxes Gigas

Peter Makovicky is a University of Minnesota Twin Cities researcher that’s been working on the remains of Meraxes gigas. With Juan Canale and Sebastian Apesteguía, his Argentinian colleagues, he co-leads the team that initially discovered the dinosaur’s remains in 2012. Most of the analysis revolves around discovering more about the biology and evolution of massive prehistoric carnivores, such as Tyrannosaurus rex and Carcharodontosaurus.

Meraxes Gigas is now part of the Carcharodontosauridae family. This massive group includes carnivore Saurischians you may know, such as Giganotosaurus, Tyrannotitan, Neovenator, and Shaochilong. One thing they have in common with each other and the Tyrannosauridae family is that they have huge skulls and short arms.

Of course, you’ll know the Giganotosaurus from Ark: Survival Evolved, the popular video game where you can tame and live among dinosaurs. Another star-stellar appearance is in the latest blockbuster movie, Jurassic Park: Dominion. 

The rocks where the researchers found the remains are over 90 million years old. Meraxes Gigas is a massive dinosaur, while not as huge as some of the other carcharodontosaurids. The most impressive part of this discovery is that the remains form the most complete skeleton of this dino family in the southern hemisphere, which is why it’s so important.

Short arms and prehistoric meat eaters

The question that Meraxes Gigas is helping to answer is why prehistoric carnivores had such small arms. According to Peter Makovicky, it’s actually related to the size of the skull:

“The neat thing is that we found the body plan is surprisingly similar to tyrannosaurs like T. rex. But, they’re not particularly closely related to T. rex. They’re from very different branches of the meat-eating dinosaur family tree. So, having this new discovery allowed us to probe the question of, ‘Why do these meat-eating dinosaurs get so big and have these dinky little arms?”

Sebastian Apesteguía also had his part to add to the research documentation:

“The discovery of this new carcharodontosaurid, the most complete up to now, gives us an outstanding opportunity to learn about their systematics, paleobiology, and true size like never before.”

So what do they propose? Well, when comparing the three therapod families, it seems that their skulls grew larger as they evolved. Since they had huge predatory teeth inside these massive heads, they didn’t need such large arms anymore. It could have been that their arms with much longer when the carnivores first appeared when compared to the time of the extinction event.

Here’s what Peter had to say:

“What we’re suggesting is that there’s a different take on this. We shouldn’t worry so much about what the arms are being used for, because the arms are actually being reduced as a consequence of the skulls becoming massive. Whatever the arms may or may not have been used for, they’re taking on a secondary function since the skull is being optimized to handle larger prey.”

The analysis and research methods

One of the approaches was a phylogenetic analysis, whereby characters were added to the Canale et al. data matrix. Some of the more scientific details included discussions around Carcharodontosaurid nasals, parietal posterior projection, scapular blade dorsal and ventral margins, and the astragalar ascending process.

Another approach was histological analysis, where they looked at primary tissue that still remained in the fibula remains. They also investigated growth curves, age retrocalculations, and comparisons with other similar theropods, such as Tyrannosaurus and Giganotosaurus. 

More Scientific Details on Meraxes Gigas

If you’ve read the novel series Song of Ice and Fire, then you may recognize Meraxes as the name of one of the dragons. Yes, the genus was named after that draconian lizard from the famous fantasy series. As for the species name, gigas is from the Greek word that means giant and refers to the size of Meraxes Gigas.

The holotype is described in the Current Biology journal as follows:

“MMCh-PV 65 (Museo Municipal “Ernesto Bachmann,” Villa El Chocón, Neuquén, Argentina), nearly complete skull without mandibles, pectoral and pelvic girdles, fore- and hindlimbs, fragments of cervical and dorsal vertebrae, complete sacrum, and proximal and middle caudal vertebral series.”

This specific specimen was discovered in Upper Cretaceous Huincul Formation of northern Patagonia, Argentina, which is where the research team recovered the fossils.

Some comparisons with other prehistoric carnivores

The journal also highlights some interesting comparisons with other therapods, besides the short arms, which we’ll quickly summarize here:

• Acrocanthosaurus: similar skull shape and proportions; shorter paroccipital process and less ventrally angled; extensively pneumatized palatine; co-ossified sacral vertebrae
• Giganotosaurus: wide parietal skull table; conspicuous knob dorsally on the supraoccipital; fully ossified interorbital septum with parasphenoid-basisphenoid complex; co-ossified sacral vertebrae
• Carcharodontosaurus saharicus: wide parietal skull table; conspicuous knob dorsally on the supraoccipital; fully ossified interorbital septum with parasphenoid-basisphenoid complex
• Neovenator: extensively pneumatized palatine
• Allosaurus: robust medioventral crest, although more prominent; strongly developed flexor tubercle, although larger

Final Thoughts

These new discoveries on Meraxes Gigas really shed new light on why these prehistoric carnivores might have had small arms. With the skulls growing, they no longer needed long arms. It’s interesting to see how it compares to other dinosaurs in related families, especially our buddies T-Rex and Giganotosaurus. We’ll keep you updated if we hear any more revelations from the research team.

News source: University of Minnesota Twin Cities

Research journal: Current Biology

Images courtesy of University of Minnesota Twin Cities and Current Biology