(WGHP) — Tyrannosaurus rex.

The name conjures up a specific mental image in most everyone. Particularly 8-year-olds.

The mighty Tyrannical Lizard King stomped across North America millions upon millions of years ago. But was it alone?

A new study is proposing that “rex” may not have been the only Tyrannosaurus on the block.

“The name Tyrannosaurus rex, or T. rex for short, has two parts,” says Scott Persons, a College of Charleston geology professor and an author of the new study. “Tyrannosaurus – that’s the ‘T.’ – is the name of the genus. The ‘rex’ identifies a species within that genus.”

“It’s a cool name – it has what I’d call rex appeal,” continues Persons. “But maybe not every Tyrannosaurus deserved that “rexy” name. Within a genus there are usually multiple species that vary from one another. We Homo sapiens share our genus with many hominid relatives – like Homo neanderthalensis, Homo erectus and Homo habilis – but there has only ever been one recognized species of Tyrannosaurus.”

Researchers have proposed that the variations in size and shape between different Tyrannosaurus specimens are well beyond what could be expected for one species, compared to similar dinosaurs like Allosaurus and Tarbosaurus.

As a result of these findings, the researchers have theorized that the specimens we have could represent a few distinct species under the genus of Tyrannosaurus. 

Bulkier specimens with a double row of chisel-shaped teeth were discovered in deeper, older sites. Skinnier, lighter-boned specimens and bulky specimens with only a single row of teeth came from ‘younger’ points in time. 

The researchers have proposed new names to reflect the variety: “Tyrannosaurus imperator,” for the older, double-toothed specimens, “Tyrannosaurus regina” for the lighter boned specimen and the classic “Tyrannosaurus rex” for the bulky, younger specimens with a single row of teeth, as that is what the first Tyrannosaurus skeleton unearthed was. 

These researchers hypothesize that Tyrannosaurus imperator may have been an ancestral species to the others. 

Whether or not it’s multiple species, Tyrannosaurus existed in North America for 1.5 million years. 

“From an evolutionary perspective, that’s a long time for one species of large, warm-blooded predator to remain unchanged,” says Persons. “Natural selection often leads to expanding diversity. Today, lions and leopards are two species of the same genus that live together, as are grizzly bears and black bears. I think it’s unlikely that all our Tyrannosaurus specimens represent a single species. The challenge is trying to tell them apart.”

This is all just hypothetical. Persons doesn’t think it’s likely that museums will be rushing to re-designate their Tyrannosaurus exhibits. 

“In paleontology, all species names represent hypotheses,” he says. “After all, no amount of romantic lighting or Barry White will reveal to you which Tyrannosaurus fossils could mate and yield fertile offspring. But, like any good scientific hypothesis, ours can be tested. As new Tyrannosaurus skeletons are found, we can check if they fit or defy the three proposed species and associated traits. That will make the next discovered Tyrannosaurus skeleton all the more exciting.”