The fearsome Tyrannosaurus rex was first described by scientists more than a century ago. After that, however, additional tyrannosaur relatives were slow to surface, leaving important details about the group unknown.

But in the past year half a dozen new tyrannosaur species have been described, and during the past decade the known diversity of tyrannosaurs has more than doubled. These finds have fleshed out details about the emergence of their kind over evolutionary time, including the quintessential carnivore.

Researchers studying tyrannosaurs have had a leg up over those working on other dinosaurs—and even some extant animals—given T. rex's wide popularity. "Its star power has allowed a research focus into questions not normally undertaken with fossils, questions like bone growth, biomechanics and neurology," paleontologist Mark Norell, of the American Museum of Natural History in New York City and a co-author of a new paper examining developments in the tyrannosaur field, said in a prepared statement.

"We know more about tyrannosaurs than any other group of dinosaurs—even more than some groups of living organisms," Stephen Brusatte, a graduate researcher with the museum and co-author of the new paper, said in a prepared statement. And the multitude of new discoveries and advanced analysis tools has allowed researchers to "understand the family tree of tyrannosaurs in unprecedented detail."

The new review article, published online September 16 in Science, assembles data about the 20 known tyrannosaur genera—some of which are about one hundredth of the size of T. rex and others which lived 100 million years before it—to paint a clearer picture of tyrannosaur evolution and biology.

"T. rex is really just the tip of the iceberg of tyrannosaur diversity," Brusatte noted.

View a slide show of some lesser-known tyrannosaurs that have helped researchers piece together new clues about T. rex