Although 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 have been found in Europe, South America, China, Japan and Australia. However, this is the first time a neovenatorid has ever been found in North America.
Siats terrorized what is now Utah during the Late Cretaceous period (100 million years ago to 66 million years ago). It was previously unknown who the top meat-eater was in North America during this period. "Carcharodontosaurs reigned for much longer in North America than we expected," says Zanno. In fact, Siats fills a gap of more than 30 million years in the fossil record, during which time the top predator role changed hands from carcharodontosaurs in the Early Cretaceous to tyrannosaurs in the Late Cretaceous.
The lack of fossils left paleontologists unsure about when this change happened and if tyrannosaurs outcompeted carcharodontosaurs, or were simply able to assume apex predator roles following carcharodontosaur extinction. It is now clear that Siats' large size would have prevented smaller tyrannosaurs from taking their place atop the food chain.
"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," says Makovicky. Zanno adds, "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."
At the time Siats reigned, the landscape was lus
|Contact: Tracey Peake|
North Carolina State University