For decades, paleontologists and dinosaur aficionados alike have debated what is the largest land-dwelling carnivore of all time. In the a single corner, there’s Tyrannosaurus rex, the terror of prehistoric North The usa. In the other, Giganotosaurus — an equally large dinosaur that stalked historic Patagonia, and a single of the last of an spectacular lineage that ruled for tens of millions of decades before tyrannosaurs rose to prominence.

To paleontologists, Giganotosaurus and its family members are categorized as carcharodontosaurs. Their identify suggests “shark-toothed lizard,” set up by the discovery of Carcharodontosaurus itself in 1931. But even as gurus identify new species from the U.S., Europe, South The usa, Africa, and Asia, these momentous meat-eaters can by no means pretty seem to be to action out of the shadow of tyrannosaurs. That’s a shame. For millions of decades, the predicament was the other way all over.

Place the Variations

Giganotosaurus at Fernbank

Giganotosaurus skeleton mount at the Fernbank Museum of Purely natural Record in Atlanta, Georgia. (Credit history: Jonathan Chen/Wikimedia Commons)

On the surface, a single huge, large-toothed dinosaur may possibly seem to be the very same as another. “If you just glance at a Carcharodontosaurus, you may possibly think it is a T. rex,” says College of Edinburgh paleontologist Stephen Brusatte. Equally walked on two legs, had tiny arms and were being geared up with powerful jaws whole of menacing enamel. But, inspected much more intently, these carnivores are incredibly various.

The enamel of T. rex, for example, are comparatively thick. Brusatte phone calls them “banana-shaped pegs.” But carcharodontosaurs bought their identify from enamel that were being thinner from side-to-side and came to a sharper point, superior for reducing flesh than pulverizing bone. Similarly, notes paleontologist Elena Cuesta, the skulls of carcharodontosaurs really don’t have as quite a few air pockets within — the shark-tooths’ skulls seem to be to be a minor more robust, allowing them provide powerful bites.

Some differences in the neck vertebrae, far too, indicate that the shark-toothed hunters had a minor much more neck agility than T. rex, potentially using powerful neck muscle tissues to help set additional energy powering their chomps. This difference in agility extends to the standard make of each dinosaur, far too. T. rex is a bulkier, heavier dinosaur that most likely was not ready to transfer pretty so quick, even though carcharodontosaurs have skulls and body proportions that are a minor much more svelte and less burly.

And even though T. rex was a dinosaur suited to provide bone-crushing bites and thoroughly just take apart carcasses, carcharodontosaurs could have been specialists in getting down and tearing apart the long-necked dinosaurs they lived together with. These various carnivorous routines are on exhibit among animals even today, this sort of as these between noticed hyenas and lions.

Dueling Dinos

Concavenator corcovatus thermo

Concavenator corcovatus using its hump as a thermoregulatory device, absorbing sunlight in the heat of a morning dawn. (Credit history: Emily Willoughby/Wikimedia Commons)

Above time, both equally tyrannosaurs and carcharodontosaurs thrived in the Mesozoic world, but in a back-and-forth dance that performed out in excess of time and house. The earliest tyrannosaurs were being tiny, raptorlike animals that advanced all over 160 million decades back. They lived less than the feet of larger sized carnivores like Allosaurus, a stand-in for what the ancestors of carcharodontosaurs were being like. The shark-toothed dinosaurs, by contrast, ongoing the development of their allosaur ancestors and became the dominant carnivores in excess of much of the earth during the Early Cretaceous.

To day, the earliest trace of the carcharodontosaurs comes from southeastern Romania. It is a tooth estimated to be much more than 132 million decades aged, from the earliest section of the Cretaceous, and had beforehand been misidentified as that of a various carnivorous dinosaur. The very same happened to a much more finish locate in Internal Mongolia. Paleontologists had uncovered the bones of a large carnivore that had some thing of an id crisis — some gurus noticed it as an allosaur, other folks as a tyrannosaur, and some believed it was a raptor. But in 2009, Brusatte and colleagues redescribed the fossil as the oldest definitive carcharodontosaur, which they called Shaochilong.

Other finds have stacked up in the latest decades. Some of these carnivores were being absolutely great, with Giganotosaurus and Carcharodontosaurus becoming equivalent to Tyrannosaurus in dimension. Some were being scaled-down but bore weird ornaments. Acrocanthosaurus from the U.S., and Concavenator from Spain, bore elevated spines along their backs that supported sail-like constructions. No a single is pretty absolutely sure why these ornaments advanced. But a single detail is clear: These dinosaurs lived large at a time when the ancestors of T. rex were being meek and tiny, and they could have drastically motivated the historical past of other carnivores.

“There was nothing inevitable about the rise of tyrannosaurs,” Brusatte says. In point, it appears to be that the carcharodontosaurs held them back. Take into account some the latest finds from the desert of japanese Utah. Paleontologists recently identified a human-sized tyrannosaur named Moros from these rocks. At all over the very same time, there roamed Siats — a carcharodontosaur about the dimension of a college bus. Right here, and in other areas all over the world, the shark-toothed hunters took in excess of the huge apex predator market to start with and kept other hunters out.

“It appears to be like tyrannosaurs exploded to massive dimension only following the carcharodontosaurs went extinct, or became much less frequent,” Brusatte says.

The dominance of the carcharodontosaurs could have also restricted the enlargement of tyrannosaurs into the Southern Hemisphere. To day, the only proof of these tyrants underneath the equator is a questionable fossil from Australia. It could be, Cuesta says, that carcharodontosaurs and other large predators — this sort of as the unusual, horned abelisaurids — could have prevented tyrannosaurs from gaining a claw maintain. The photograph could improve with new finds. “The fossil record is annoyingly patchy and incomplete,” Cuesta says, but the latest pattern suggests that tyrannosaurs essential other large carnivores to get out of the way before they could just take in excess of that job between eighty million and sixty six million decades back.

Irrespective of their importance to historic foodstuff webs, even though, paleontologists are really just having to know these titanic hunters. They must have hunted and fed in a various way than tyrannosaurs — their skeletons make that clear. But, Brusatte notes, “I’d love to know if carcharodontosaurs really did hunt the colossal titanosaurian sauropods,” or immense long-necked dinosaurs that occupied the very same habitats.

Even the large dimension of these animals raises
a mystery: If carcharodontosaurs, tyrannosaurs, and some other theropods maxed out all over the forty-foot mark, does this symbolize some type of biological limit to how large huge carnivores can be? The tale remains in the bones, which inform the tale of some of the most monstrous predators of all time.