Suskityrannus hazalae isn't the first or even smallest of the Tyrannosaurus family tree, but Nesbitt said it provides the best example of how this family of modest-sized dinosaurs evolved into the towering T. rex.
The study's lead author, Sterling Nesbitt, a paleontologist at Virginia Tech in the United States, said that the fossils of the smaller T. rex cousin could provide one of the best examples yet as to how a smaller family of dinosaurs evolved into monstrous super predators.
Nesbitt found a set of its bones in 1998 when he was 16, while serving as a volunteer on a dig in New Mexico with a famed paleontologist.
Sterling Nesbitt, an Assistant Professor of Geobiology at Virginia Tech, sits for a photo next to the fossilized bones of Suskityrannus hazelae, a miniature adult Tyrannosaurus dinosaur relative. The new dinosaur is called Suskityrannus hazelae, named after the Zuni word for coyote. The duck-billed dinosaur dates back 92 million years, about 20 million years before the T. rex stomped the Earth. But for about two decades, scientists weren't certain what it was, until other small cousins of T. rex were discovered.
In fact, the first partial skull of the mini tyrannosaur was found in 1997 by Robert Denton, now a senior geologist with Terracon Consultants, an engineering consulting firm in New Jersey.
Monday's report said that Suskityrannus hazelae provides an intermediate link between older, smaller tyrannosaurs and the big, last-surviving members of the species.
The newly discovered cousin - which was three times longer than it was tall - weighed between 45 and 90 pounds, nearly nothing compared to the nine-ton king of the dinosaurs.
Smithsonian Institution paleobiologist Hans Sues, who wasn't part of the study, said it was an important find. "Suskityrannus is the first really good record of the early tyrannosaurs in North America", he wrote in an email. T. rex weighed around 9 tons and measured about 40 feet (12 meters) in length.
Although the discovery helps with understanding how the T. rex evolved, paleontologists have said that it is still unclear as to why the smaller carnivorous dinosaurs evolved to become so large.