The Largest Carnivorous Dinosaur May Not Have Been T. Rex

Tyrannosaurus rex has been a media darling since (arguably) 1906, when The New York Times called it "the prize fighter of antiquity."

Named just one year prior, this apex predator was already making a splash over at the American Museum of Natural History in Manhattan, where a preserved Tyrannosaurus specimen is kept to this day. Many decades after its debut, T. rex was the largest known carnivorous dinosaur. In later generations, the theropod dinosaur became immortalized in the "Jurassic Park" franchise.

Today we know an adult T. rex could stand 12 feet (or 3.6 meters) tall at the hip and measure 40 feet (12 meters) long. As such, the enormous size of Tyrannosaurus made it one of the largest carnivorous dinosaurs to ever walk the Earth.

But hold your horses. A handful of other carnivorous dinosaurs rivaled, or possibly exceeded, the creature in size. Giganotosaurus belongs to this elite group — and it's part of a dinosaurian mystery that's never been solved.

T. rex and Giganotosaurus were both representatives of the theropoda clade. (A "clade" is a group of organisms which includes a common ancestor species and all of its closely related descendants.) Hollow-boned and bipedal, the theropod dinosaurs were (and are) a highly successful bunch.

There was also massive size variation present in the clade, with the smallest raptors being roughly the size of modern dogs, and the largest theropod dinosaurs growing to the size of a modest house. On the list of documented theropods, you'll find every carnivorous dinosaur yet discovered, quite a few plant-gobbling species and all birds, living and extinct.

Tyrannosaurus rex and most other dinosaurs were wiped out at the close of the Cretaceous period, an expanse of geologic time that lasted from 145 to 66 million years ago. Its conclusion marked the end of the Mesozoic Era of Earth's history, sometimes called "The Age of Dinosaurs."

Tyrannosaurus rex, long thought to be the biggest carnivorous dinosaur, lived in North America during the twilight of the Cretaceous, making its evolutionary debut around 68 million years ago. Our buddy Giganotosaurus was the product of another time — and a different landmass.

Giganotosaurus Habitat

Native to western Argentina, it came along in the early Cretaceous period, roughly 98 to 97 million years ago. South America was a realm of giants back then. Huge sauropods, or "long-necked" herbivorous dinosaurs, roamed the countryside.

Some of these plant eaters — like Andesaurus and Limayasaurus — stretched around 50 feet (15 meters) long, making them some of the largest dinosaur species themselves by body size. Rounding out the local bestiary were other animals like crocodylians, early snakes and beaked herbivores.

Discovering the Largest Carnivorous Dinosaur to Date

No doubt Giganotosaurus kept its neighbors on guard. The discovery of the holotype specimen was first announced in 1995 by paleontologists Rodolfo A. Coria and Leonardo Salgado.

In all the years since, we have yet to find a complete skeleton. However, the fragmentary remains of backbones and tail vertebrae at our disposal suggest Giganotosaurus was at least 41 feet (12.5 meters) in length according to size estimates. So Giganotosaurus might've been slightly longer than T. rex, making it a contender for the largest carnivorous dinosaur.

On the other hand, a 2014 paper published in the journal Plos Biology, argued T. rex had a much heavier build. Using the circumference of its upper leg bones, Roger Benson and his colleagues calculated that a mature Giganotosaurus had a body mass of about 13,448 pounds (6,100 kilograms). The same technique put T. Rex at a whopping 16,975 pounds (7,700 kilograms).

Whichever species is truly the largest meat eating dinosaur, we know that that they were truly giants for their time. These calculations are done using imperfect data, so we can't know Giganotosaurus' exact size until there is a near-complete specimen found of the large theropod.

Weight gaps are all well and good, but the jaws tell better stories. Anatomical evidence suggests these two carnivorous dinosaurs used very different methods to bring down their prey. Thick and banana-shaped, the sharp teeth of Tyrannosaurus would've excelled at crushing bone.

In contrast, Giganotosaurus had tall, skinny teeth which looked an awful lot like recurved kitchen knives. Serrated on both sides, the pearly whites were housed inside a narrow snout and crocodile-like jaws. By the way, Giganotosaurus had a monstrous skull; scientists estimate the noggin was around 6 feet (2 meters) long.

Combine these features and you're looking at theropod dinosaurs that probably killed by slicing ribbons of meat off its unfortunate prey — as opposed to shattering bones. Once bitten, a victim may have bled out while the carnivore lurked nearby.

Great White Relatives

Giganotosaurus hails from one of the fossil record's most intimidating families, the carcharodontosaurids. If you're into sharks, that name should ring a bell: Scientists call the great white Carcharodon carcharias. Likewise, the word "carcharodontosaurid" roughly means "shark-toothed lizard" in Greek.

Steve Brusatte is a paleontologist at the University of Edinburgh who's studied these remarkable theropod dinosaurs — and happened to be a scientific adviser for one of the "Jurassic World" movies.

"The roster of carcharodontosaurid fossils has expanded tremendously over the last decade as people have found more fossils all over the world, particularly in South America and Africa, but also in Asia and Europe," says Brusatte in an email.

"Most carcharodontosaurids [like Giganotosaurus] were giant meat-eating dinosaurs with deep jaws and sharp, thin, almost shark-like teeth. They were the largest and most formidable predators in many ecosystems during the early to middle part of the Cretaceous, before the rise of tyrannosaurs."

Indeed, T. rex had some puny forebears. The first members of its lineage were human-sized predators that showed up around 170 million years ago in the late Jurassic period. The giant T. rex wouldn't start evolving until the late Cretaceous Period, after the mighty carcharodontosaurids died out.

"This changeover remains a mystery," explains Brusatte. "We don't really know why it happened, and it is one of the biggest remaining mysteries of dinosaur evolution, in my opinion."