The discovery of a new species of carnivorous dinosaur has turned what had been current paleontological thinking on its head. A newly discovered species, Siats meekerorum, (pronounced ‘see-atch’) was, it turns out, the apex predator of its time, and kept tyrannosaurs from assuming the top predator role it was assumed to have held.
Humorously named after a cannibalistic man-eating monster from Ute tribal legend by Peter Makovicky of Chicago’s Field Museum of Natural History, Siats is a species of carcharodontosaur, giant meat-eaters that are some of the largest predatory dinosaurs thus far discovered. The only other carcharodontosaur known from North America is Acrocanthosaurus, which roamed eastern North America more than ten million years earlier. Siats is only the second carcharodontosaur ever discovered in North America, apart from Acrocanthosaurus, discovered in 1950. One of the three largest ever discovered in North America, Siats lived alongside and competed with the comparatively small-bodied tyrannosaurs 98 million years ago.
“You can’t imagine how thrilled we were to see the bones of this behemoth poking out of the hillside.” Dr. Lindsay Zanno, a North Carolina State University paleontologist with a joint appointment at the North Carolina Museum of Natural Sciences told the Washington Times. “It’s been 63 years since a predator of this size has been named from North America.”
Zanno and Makovicky discovered the partial skeleton of the new predator in Utah’s Cedar Mountain Formation in 2008. The recovered specimen would have been more than 30 feet long and weighed at least four tons. Yet, in spite of its giant size, its bones are those of a juvenile.
Zanno and Makovicky theorize that adult Siats ultimately became the same size as Acrocanthosaurus, which means that the two species vie for the second largest predator ever discovered in North America. Tyrannosaurus Rex, which holds first place, came along 30 million years later and weighed in at more than twice that amount.
Still, Siats and Acrocanthosaurus are both carcharodontosaurs. They belong to different sub-groups. Siats is a member of Neovenatoridae, a more slender-bodied group of carcharodontosaurs.
Neovenatorids may have been found in Europe, South America, China, Japan and Australia previously. However, it was a surprise discovery when a neovenatorid were found in North America.
Siats terrorized what is now Utah during the Late Cretaceous period between 100 million years ago to 66 million years ago. Prior to this, no one knew exactly who the top meat-eater was. “Carcharodontosaurs reigned much longer in North America than we expected,” says Zanno. Yet, in a scholarly way, Siats’ discovery fills an empty husk of knowledge. A gap of more than 30 million years in fossil records during which time the top predator role changed hands from carcharodontosaurs in the Early Cretaceous to tyrannosaurs in the late Cretaceous period.
Without fossils paleontologists are never quite sure about when specific change happened in a concrete way. “The huge size difference suggests that tyrannosaurs were held in check by carcharodontosaurs, and only evolved into enormous apex predators after the carcharodontosaurs disappeared,” Makovicky told the Washington Times. Or, as Zanno reiterated, “Contemporary tyrannosaurs would have been no more than a nuisance to Siats, like jackals at a lion kill. It wasn’t until carcharodontosaurs bowed out that the stage could be set for the evolution of T. Rex.”
When Siats ruled, the landscape was lush like the Amazon Basin, richly endowed with an abundance of vegetation and a massive water supply that allowed for the support of thousands of plant-eating dinosaurs, turtles, super-sized crocodiles, and giant, possibly amphibian lungfish. When comparing this lush jungle life with what occurred in Central and South America, the model insists that all kinds of predators survived as a part of this ecosystem, including early tyrannosaurs and several as yet unnamed, unknown species of other feathered dinosaurs that have yet to be described by the team.
