Though the discovery of dinosaur fossils is always an exciting event, the remains of one that roamed North America about 100 million years ago, is even more so. That's because while paleontologists have extensive knowledge about the Tyrannosaurus-rex that dominated the arena in the late Cretaceous period (about 60 million years ago), very little is known about the ones that ruled the roost during the intermediate period.

This gap in knowledge of what scientists often refer to as the last phase in the so-called 'Age of Dinosaurs', has now been filled to a certain extent, thanks to the discovery of the fossils of a massive meat eating predator. Paleontologists have named it Siats meekerorum after the man-eating monsters in a Ute tribal legend and the Meeker family, which has supported early career paleontologists at the museum.

The saga of this exciting find that was reported in the November 22nd edition of Nature Communications began in the summer of 2008. Lindsay Zanno from North Carolina Museum of Natural Sciences and Peter Makovicky from the Chicago Field Museum of Natural History were conducting an excavation in the hot deserts of Eastern Utah, when Lindsay came across a collection of bone fragments on the surface of the Cedar Mountain Formation. While remains of large dinosaurs are rare in these rocks, the scientists suspected that they had stumbled upon something that may help provide insight into the creatures, that lived between 90-100 million years ago.

However, before they could unearth anything, the excavating season was over and the paleontologists had to return to their respective jobs.

It took two more summers before Lindsay and her team were finally able to extract the partial skeleton that included the vertebrae, parts of the hip, the lower leg and toes - all perfectly preserved by the rocks for more than 100 million years.

Initially, the scientists thought the remains were those of an Ankylosaurus or T-rex. However, upon closer examination they realized that the fossils belonged to a member of the Carcharodontosaurus family. Related to the giant Giganotosaurus, it was a carnivore that inhabited Argentina during the late Cretaceous period.

Judging from the size of the fossils, Siats is believed to be the third largest predator ever found in North America. Scientists estimate that it was about 30-feet long and weighed 4 tons. But given that they are calculating the size from the fossil finds of a juvenile, it is entirely possible that fully-grown adult Siats were even larger. The dinosaurs probably had a sharper, less blocky head than the tyrannosaurs and long three-clawed arms, very different from the short ones sported by the mighty T-rex.

The researchers are not sure if the Siats meekeroum lived alongside the T-rex, but thanks to other fossils discovered in the same area, they do know that it shared the land with some smaller tyrannosaurs. This confirms their suspicion that at one time the Siats meekeroum was at the top of the predatory food chain. As to how they became extinct and made way for the tyrannosaurs to evolve into the mega predator T-rex, is a mystery that paleontologists hope to solve with future finds.

Resources: wired.com, cnn.com.sciencedaily.com