Tyrannosaurus rex may have been three species, scientists claim

Kieran Galpin

At least three species are said to have existed

Tyrannosaurus rex is arguably the most famous dinosaur to ever walk the Earth – but now, 65 million years after they were munching everything in their path, scientists believe it could’ve been three separate species.

Writing in the journal Evolutionary Biology, Gregory Paul and his team analysed fossils which led them to such a monumental conclusion. Previously, palaeontologists had studied T rex remains from different rock layers, said Paul, who also worked on Jurassic Park as a dinosaur specialist.

“That may not be a good idea to do because you may be [looking at] different species,” he said.

T Rex are one of the few dinosaur species believed to have only had one primary species over their one million-or-so dominant years. However other behemoths of pre-historic history like the triceratops evolved into numerous species – so why didn’t rexxy?

Well, that’s just it; scientists think they did.

Studying 37 sets of remains, Paul and colleagues looked at the length and circumference of thigh bones as they are available for two-thirds of T rex specimens.

“We found that the robustness in the sample we have of tyrannosaurus, the variation of the femur is greater than all other tyrannosaurids combined over 10m years of evolution,” said Paul. “You can’t just not pay attention to that.”

Their study found that varied thigh bones do not link to the overall size of the creature, nor how mature the T rex was when it died. The uneven ratio of bones does not suggest that the sex of the animal created the variation either.

Bones considered more “gracile” or slender were found to possess higher levels of sediment and regardless of how robust the bones were, most specimens had only one incisor-like tooth in the lower jaw.

While Paul and his team are not yet certain, they hypothesise that specimens found in lower layers are that of another species – the Tyrannosaurus imperator.

This colossal beast’s name translates to tyrant lizard emperor, so count us lucky they died out millennia ago. The stocky-boned dinosaur remains are believed to be from the regular Tyrannosaurus rex and the final “gracile” framed creature is believed to have been Tyrannosaurus regina, the tyrant lizard queen.

That isn’t to say the theory lacks opposition.

Professor Steve Brusatte from the University of Edinburgh told the Guardian: “I understand the temptation to divide T rex into different species because there is some variation in the fossil bones that we have. But ultimately, to me, this variation is very minor and not indicative of meaningful biological separation of distinct species that can be defined based on clear, explicit, consistent differences.”

Prof Thomas Carr, a T rex expert at Carthage College in the US, added: “I found no evidence of more than one species. And if that signal was in the data, I would have picked it up.”