A “tyrant lizard king” ruled western North America more than sixty-six million years ago. But how large was this monarch’s royal family? Could what we call a T. rex today, possibly be composed of multiple species? For more than two decades, the Field Museum in Chicago has displayed a T. rex nicknamed “Sue”, but now a new study argues that Sue is not actually a Tyrannosaurus skeleton but a related species nicknamed the “Tyrannosaurus Imperator”. In a new study in the journal Evolutionary Biology, three paleontologists argue that the fossils that are assigned to the T. rex cluster into three different body types, which further represent three separate and different species. “For Tyrannosaurus, all the specimens from North America have been put into the same species, T. rex and that’s become something of a problem because nobody was testing whether that was really true or not,” says the study leader, a paleoartist, Gregory Paul. Paul and his co-authors contend that their findings, if validated, would sharpen our view of dinosaur evolution during the Cretaceous, which lasted from 145 million to 66 million years ago. “We are curious about the likelihood of trying to ascertain very fine level species-to-species evolution,” says study co-author Scott Persons, a palaeontologist at the school of Charleston in South Carolina. They would reclassify some of the famously known Tyrannosaurus fossils on display if results are valid.