'Man-Eating Monster' Dinosaur Was Top Predator Before T. Rex; Discovery Solves 30 Million Year-Old Puzzle

By Ajit Jha on November 22, 2013 8:34 AM EST

Siats meekerorum
In this artistic rendering, a Siats meekerorum stands over it's most recent kill, while small tyrannosaurs look on in dear of the giant predator. (Photo: JULIO LACERDA — Courtesy of th)

Paleontologists have been trying for decades to piece together all the links in the gigantic, yet mysterious world of dinosaurs. These colossal reptiles indulged in fratricidal intra-species war of eventual extinction, so each new discovery into their world is more intriguing than the last. The latest find to thrill paleontology community — and all dino lovers — is a new species of carnivorous dinosaur, one among the largest three ever discovered in North America. Called Siats Meekerorum, they dominated their habitat for millions of years, and intimidated their contemporary competitor predator tyrannosaurs for millions of years.    

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The "Siats" part of the name derives from mythical cannibalistic man-eating monster of the Ute tribal legend. The Ute people originally occupied large parts of what is today Eastern Utah, Western Colorado, and parts of New Mexico and Wyoming. The partial skeleton of this new predator was discovered in 2008 in Utah's Cedar Mountain Formation in 2008. The work on the skeleton was led by Lindsay Zanno, a North Carolina State University paleontologist with a joint appointment at the North Carolina Museum of Natural Sciences, and lead author of a Nature Communications paper describing the find, and colleague Peter Makovicky, from Chicago's Field Museum of Natural History. The Meeker family who supported the early career paleontologists is acknowledged in the second half of the species name. 

Siats, who lived 98 million years ago, were a carcharodontosaur species, among the largest (in size) predatory carnivores ever discovered. Next to this newly discovered monster, the only other known carcharodontosaur to roam North America over 10 million years earlier is Acrocanthosaurus. This was also the first reptile of this giant species discovered in 1950.

"It's been 63 years since a predator of this size has been named from North America," said Zanno in a press release"You can't imagine how thrilled we were to see the bones of this behemoth poking out of the hillside."

Measuring 30 feet long and weighing at least four tons, the gigantic recovered specimen is actually thought to be a juvenile. The adult Siats could possibly match the size of Acrocanthosaurus, according to Zanno and Makovicky. In other words, archarodontosaur compete with Acrocanthosaurus for the second-largest sized predator ever discovered in North America. First place, of course, is still held by the Tyrannosaurus rex, that weighed at least eight tons and came 30 million years later. 

Siats are a member of a more slender-bodied group of carcharodontosaurs known as Neovenatorids that have already been found in Australia, Japan, China, South America and Europe.This, however, is the first time that a neovenatorid has been found in North America. Siats are thought to be ferocious predators that terrorized the present Utah region during the Late Cretaceous period, estimated between 100 million years to 66 million years ago. With the discovery of Siats, a missing link of over 30 million years of fossil record is nearly identified. Paleontologists now know the top carnivorous in North America during this period. "Carcharodontosaurs reigned for much longer in North America than we expected," said Zanno. After their 30 million year reign, carcharodontosaurs in the Early Cretaceous gave up their top dog status to tyrannosaurs in the Late Cretaceous. 

It was previously hypothesized that some sort of smaller tyrannosaur were at the top of the food chain during the Early Cretaceous, but paleontologists are now pretty sure Siats claimed that role. "The huge size difference certainly suggests that tyrannosaurs were held in check by carcharodontosaurs, and only evolved into enormous apex predators after the carcharodontosaurs disappeared," said Zanno. "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."

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