Giganotosaurus vs. T. rex: Who would win in a battle of the big dinosaurs?

Picture this: Two dinosaurs with massive teeth and hulking figures circle each other, threatening a smackdown. Each was the most successful predator of its time. In a ferocious duel of the dinosaurs—Tyrannosaurus rex vs. Giganotosaurus carolinii—which would emerge alive? 

Both species enter the ring with experience as apex predators that hunted some seriously impressive prey. T. rex is thought to have eaten armored Triceratops and big-brained duck-billed dinosaurs, while Giganotosaurus probably took down the largest-ever land animals: the long-necked sauropod dinosaurs, which could’ve been 10 times the predator’s size. None of these dinos would’ve been an easy meal. So what would happen if the two fearsome Cretaceous carnivores were to face off against each other?

But pitting the two against each other serves to highlight their differences, says Thomas Holtz, a principal lecturer in vertebrate paleontology at the University of Maryland who studies tyrannosaurs and their motion. This kind of thought experiment might lead to a better understanding of how these creatures followed their own evolutionary paths to become distinct, highly successful predators. 

Some of those differing characteristics might be advantageous in a rumble. But in a one-on-one fight, there is unlikely to be an obvious champion and an underdog, says Kat Schroeder, a paleomacroecologist and postdoctoral research associate at Yale University.

“They’re not fighter jets,” she says. “You can’t say this one has this absolute top speed. They’re animals. And they’re animals that lived 30 million years apart on different continents. They’re separated by 150 million years of evolution [since their last shared ancestor].”

[Related: Jurassic Park fans would love these dino discoveries]

Holtz agrees that it could be any dinosaur’s game, despite admitting professional and personal bias toward tyrannosaurs (when he was 3, he wanted to grow up to be one). “Both of them are big predators adapted to killing very large prey,” he says. “If either of them managed to get a good bite onto the other one first, they’re probably going to win.” 

What’s in a bite?

T. rex and Giganotosaurus can be described as “head hunter theropods,” Schroeder says. They both had “teeny, tiny little arms and giant heads,” she says, “so they’re probably not going to be pulling and scratching at one another.” Kicking is also out, because their feet would probably be too heavy to be of use in a fight. So there’s only one remaining option with any teeth. “They’re basically going to walk up to one another and try to grab each other with their giant mouths,” she says.

Both predators’ bites are vicious in different ways. T. rex can deliver the most skull-crushing of chomps, while Giganotosaurus’ bite leverages sharp, blade-like teeth to slash its prey’s flesh. 

T. rex’s bite force is “almost off the scale,” says Holtz. The lowest estimates for an adult’s bite force are around 34.5 kilonewtons, he says, “which is twice as strong as the bite of a saltwater crocodile, the largest reptilian predator of today.” 

[Related on PopSci+: What dinosaur fossils are we missing?]

Several adaptations in a T. rex’s head enable that smashing crunch. For one, the tyrant lizard has a long, deep snout made up of thick jaw bones, with very deeply rooted teeth. From above the gums, T. rex and Giganotosaurus would’ve appeared to have the same size teeth. But the roots of T. rex’s teeth, Holtz says, were double those of a Giganotosaurus tooth, which could be around 8 inches in total length. The largest known T. rex teeth reach 12 inches, and they’re built for impact with a round, thick shape. “T. rex has a jackhammer for a mouth,” Schroeder says. 

The T. rex’s snout was also made up of somewhat flexible bones, Schroeder says, which can be an advantage for a big bite. “A little bit of springiness allows you to bite really, really hard without breaking your own face.” 

Giganotosaurus, on the other hand, had a more forceful nip at the front of its mouth, with a long and slender snout about three times as long as it was tall. Its sharp, blade-like teeth were better at cutting than chomping down. Giganotosaurus teeth could ably slice through meat and might have been able to cause a lot of damage with a small nip.

But these dinosaurs likely wouldn’t just take turns biting each other, even locked in a cage fight. Their body size and nimbleness would also come into play.

Agility of the fighters

Jurassic Park’s Alan Grant was incorrect when he said Giganotosaurus was the largest carnivore ever to roam the Earth (that crown goes to Spinosaurus), but it was likely larger than a T. rex—at least in length. Giganotosaurus was probably about 45 to 47 feet long, while the largest T. rex specimen reached nearly 42 feet long (nicknamed “Scotty,” its bones reside at Canada’s Royal Saskatchewan Museum). Both stood about 20 feet tall, and Giganotosaurus may have had a few tons of mass on T. rex, but estimates for their maximum masses are both upward of 9 tons. 

Still, it’s unlikely that such a small size difference would give one dinosaur an edge over the other, says Holtz. What might have put T. rex in the lead, he says, was its weight distribution and resulting agility.

T. rex’s weight is concentrated toward its middle, while Giganotosaurus is “more long and slab-like throughout its body,” he says. Holtz and colleagues calculated that a T. rex could rotate its body and twist in place twice as well as other dinosaurs of a similar mass, thanks in part due to massive hip bones and muscles. The pyramid-shaped ankle bones of a T. rex also may have offered more stability for maneuvering than a Giganotosaurus’s boxier ankles, Schroeder says. “T. rex might have been able to corner a little bit better.”

Two aspects of tyrannosaurus’s evolution might explain these adaptations, Holtz suggests. T. rex’s ancestors were smaller—the ones that were around when Giganotosaurus roamed Earth were “basically dinosaurian coyotes,” he says. Or perhaps they evolved these traits to take down sophisticated prey. Triceratops, for example, was “one of the most heavily armed herbivores in Earth history,” he says, and duck-billed dinosaurs had one of the largest brain-to-body size ratios of any herbivorous dinosaur. T. rex had a bigger brain than Giganotosaurus, Holtz says, probably because it had to hunt speedier, more agile prey.

Giganotosaurus brains were half the size. “You don’t have to have a lot of focus if you’re going after walking walls of meat,” Holtz says. They came from a long line of giant predatory dinosaurs. Their “basic body plan” prepared them to hunt “long, slow-moving” herbivores, such as stegosaurs and sauropods.  

[Related: The longest dinosaur neck ever found in the fossil record]

Defeating a sauropod, which lived in a pack and may have grown up to 80 tons, would not have been easy, however, says Schroeder. Even picking off a small, young herbivore would’ve been tricky. “You’re not rolling up on a group of elephants and just grabbing a juvenile,” she says.  “You’re going to have to face off with one of these enormous animals.” 

It’s possible that this is where the slashing kind of bite comes in handy for Giganotosaurus, Holtz says. Maybe it could deliver a fatal bite quickly, he says, or perhaps its blade-like teeth could weaken the massive prey, so the carnivore could track it down to go for the kill at the right moment. 

That might be how Giganotosaurus could get the first bite on T. rex, too. The tyrant lizard had both of its eyes on the front of its face, offering better depth perception, Holtz says. But Giganotosaurus’s eyes, more toward the sides, gave better perception around their bodies. The giant southern lizard might be able to sneak-attack the T. rex, sinking its sharp front fangs into its opponent’s flank. 

If the battle occurred in one of the creatures’ home habitats, instead of in a neutral environment, that would add another dimension, Schroeder says. On Giganotosaurus’ turf, for example, T. rex might struggle with the heat and dryness of the desert in what is present-day Argentina.  

These environments, and the prey who lived there, shaped how these dinosaurs evolved. During Giganotosaurus’s time, the environment was changing dramatically with the emergence of diverse flowering plants. By the time T. rex came on the scene, however, the environment was much more stable—right up until a big rock smashed into the planet. 

There’s also a lot that remains unknown about both dinosaurs, but especially Giganotosaurus, Schroeder says. Paleontologists have found fewer of its fossils, and discuss it less frequently at conferences, likely because its homeland of South America gets less scientific attention and funding. “Paleontology tends to be a little bit North America-centric,” she says. And while “it’s fun to talk about these questions” of who would win in a fight, “we wouldn’t have any answers if we didn’t have fantastic scientists working down in South America and Africa.”