Tyrannosaurus Rex May Actually Be Three Distinct Species

A study published this week proposes three species of Tyrannosaurus instead of the long-accepted single species rex. The researchers analyzed dozens of T. rex specimens, of which there are only about 50 known to science. They found larger than expected variations in leg size and number of teeth.

Tyrannosaurus rex translates to “king of the terrible lizards,” combining the Greek tyranno (tyrant) and saurus (lizard), and the Latin rex (king). Keeping with the regal naming convention, the researchers declared the two new species Tyrannosaurus regina (queen of the tyrant lizards) and Tyrannosaurus imperator (emperor of the tyrant lizards). One species is bulky and has two sets of incisors. Now called Tyrannosaurus imperator, the oldest fossils fall into this category. T. imperator then evolved into two separate species that lived at the same time. The bulky T. rex and slimmer T. regina both had only one set of incisors.

The analysis included perhaps the most famous Tyrannosaurus fossil, SUE. Housed at the Field Museum in Chicago, it is the largest specimen ever discovered and one of the most complete. SUE is actually a Tyrannosaurus imperator according to the new study. The museum makes adjustments to SUE based on emerging research, but that doesn’t mean the signage or the dinosaur’s popular Twitter account will change anytime soon.

Tyrannosaurs skeleton in Chicago's Field Museum
Field Museum Chicago

Many paleontologists aren’t convinced. Previous studies concluded exactly the opposite, that variability in T. rex fossils is due to normal age, gender, and health differences. The study’s lead author, Gregory S. Paul, has created controversy before. He suggested other new dinosaur species in the past, some of which the scientific community rejected. Jurassic Park, both the book and movie, shouts him out as a dinosaur specialist. But he doesn’t have a formal degree in paleontology. The other authors are geologist W. Scott Persons IV and mathematician Jay Van Raalte, both from the College of Charleston.

Specimens across many scientific disciplines are often re-examined years later. In 2020, a graduate student described a new species of Thanatotheristes, a group of dinosaurs within the Tyrannosauridae family. He realized fossils found in 2010 weren’t correctly identified. For non-fossilized specimens, blood and other DNA evidence clarify species separation. But this isn’t as simple for dinosaurs, leaving room for debate.

Confusion about what is and what is not a Tyrannosaurus rex began with its very discovery. In 1905, an article described multiple species, including the first T. rex. The author later realized that the fossils were from different life stages of the same species. The name T. rex was the first on the list and so it stuck.

Whether T. regina and T. imperator will gain acceptance remains to be seen. The article appeared in the peer-reviewed journal Evolutionary Biology, which is a self-described forum for “controversial ideas in evolutionary biology.” This certainly fits the bill.

Featured Image: Universal

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