Check the toy box or shelf of most young children and their most played-with dinosaur is usually the fearsome Tyrannosaurus Rex – the biggest and the baddest of the therapods and the star villain of many dinosaur movies. Since the largest percentage of complete or nearly complete T. rex skeletons are found in North America, it would be the national dinosaur if there was such a title. Perhaps it’s a good thing there isn’t one … new research suggests that T. rex is not one but three different species and they would have to share the trophy … not to mention the movie credits.
“This paper is likely to rock the paleo community, and the public that is so used to good old T. rex.”
That paper’s lead author is Gregory Paul, an independent paleontologist and paleoartist who was also a dinosaur specialist on the film Jurassic Park. Paul and two other researchers -- W. Scott Persons IV and Jay Van Raalte – propose that there are “Multiple Lines of Morphological and Stratigraphic Evidence Support Subtle Evolution and Probable Speciation Within the North American Genus Tyrannosaurus” (the paper’s title) and they suggest the species be recategorized as three: T. rex or king, T. regina or queen, and T. imperator or emperor. Past researchers who looked at bones of T. rex from multiple layers of rock over the course of their millions of years of existence decided the various sizes were simply different ages of the same species. Paul and his colleagues disagree.
“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. You can’t just not pay attention to that.”
After studying 37 specimens currently identified as T. rex, the team noticed that the length and circumference of the thigh bones varied too much to be simply the result of the dinosaur’s age or size. While femurs found in deeper layers of rock were large and robust, those in higher, more recent layers were “gracile” or slender. Not only that, the more recent dinosaurs tended to have only one incisor-like tooth in the lower jaw, less that those from an earlier time period. If placed from earliest to latest, the earliest would be the T. imperator, followed by T. rex and then T. regina – the slender ones.
“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. Steve Brusatte, a palaeontologist at the University of Edinburgh who was not involved in the study, told The New York Times he strongly disagrees with Paul’s desire to trisect the T. rex species. Prof. Thomas Carr, a T. rex expert at Carthage College, found the study vague – he also conducted his own similar research on 31 specimens and saw no solid evidence of more than one T. rex species.
Is the research right … were there three (or possibly even more) distinct species of Tyrannosaurus rex? If so, does this mean the Jurassic Park movies and others featuring T. rex have to be remade or at least carry a disclaimer? If Disney decides to do an animation, who will provide the voice of the T. queen … and who will play the Tyrannosaurus princess?