Teen T-Rex or new species of dinosaur?: Roarrr!

No other dinosaur has been studied as much as the Tyrannosaurus Rex. But researchers do not agree on some points.

Skeleton of a Tyrannosaurus rex Photo: Koller Auctions Zurich via picture alliance

Admittedly, the Tyrannosaurus Rex was already a dangerous predatory dinosaur. But does that really warrant so much attention? The supposed king of the terrible lizards only lived for two million years before a massive boulder ended his reign 66 million years ago.

Before him, there were other large predatory dinosaurs such as Allosaurus, which hunted stegosaurs and giant long-necked dinosaurs 150 million years ago. With a length of up to 9 meters, it was hardly smaller than the Tyrannosaurus, but it still stands completely in its shadow. The Giganotosaurus, which appeared 100 million years ago in Argentina and reached a length of 13 meters, and the Spinosaurus discovered in the Sahara with its impressive dorsal sail have a similar situation.

However, if you ask children about their favorite dinosaurs, these predatory dinosaurs rarely end up at the top of the favorites ranking. There also seem to be a particularly large number of T-Rex fans among paleontologists. “There are no more studies on any dinosaur and no dinosaur receives more public attention,” says Martin Sander from the University of Bonn. That’s why hardly any paleontological press release can do without a T-Rex comparison, regardless of whether it’s about fossilized mussels or newly discovered herbivores.

How did he eat?

About 40 T-Rex skeletons were found and examined for everything imaginable. Researchers are interested in its short arms. Although they were powerful, there is disagreement as to whether they played a role in feeding or fighting. Some paleontologists believe that the arms became shorter over time to avoid injury. If several predatory dinosaurs ate a killed Triceratops at the same time, arms that were too long could quickly have gotten caught between each other’s teeth.

The diet of the predatory dinosaur is also constantly discussed. Did the T-Rex hunt its prey or did it feed primarily on carrion? The truth probably lies somewhere in between. But that’s not all: even the lips of the predatory dinosaur have become a research object. Unlike in the movies, the carnivore probably didn’t show his smile with his banana-sized teeth as aggressively. Instead, scaly lips covered its sharp teeth, with only the tips of its teeth showing, similar to today’s monitor lizard.

All of these studies are sure to make headlines and are preferred to be published in renowned research journals. A study was published in 2020 that divided all T-Rex skeletons found into three new species: the Tyrannosaurus rex, the larger Tyrannosaurus imperator and the smaller species Tyrannosaurus regina. However, this theory quickly met with great resistance from experts. The criticism: The differences in size and shape of the T-Rex bones are too small to derive new species from them. The theory of three species was therefore quickly rejected.

Another study from January 2024 is on more scientifically sound ground. It examined fossilized remains found in 1942 that had previously been attributed to an adolescent T-Rex. Researchers Nicholas Longrich of the University of Bath and Evan Saitta of the University of Chicago concluded that these bones are the remains of a smaller, distant relative, Nanotyrannus lancensis. At five meters, it was significantly smaller than the T-Rex, but it was faster and had longer arms.

This idea is not new: the Nanotyrannus was already described in 1988. However, the study provides further evidence. Among other things, the researchers examined the growth rings in the fossilized bones. They discovered that it could be an adult animal and not a growing young animal. They also compared the bones and skull with those of a young Tyrannosaurus that was still lying undescribed in a museum box. According to the study authors, there were clear differences. Longrich and Saitta are therefore convinced that 68 million years ago it was not just the Tyrannosaurus that roamed North America.

For laypeople, the knowledge that there may have been another type of predatory dinosaur may not sound particularly spectacular. However, the study reignites an old debate in paleontology. “Another common theory is that the growing tyrannosaurs also filled their own ecological niches. There would be no more room for smaller and larger predatory dinosaur species. That makes perfect sense, but it’s quite unusual for a complex ecosystem,” explains Sander. However, the paleontologist considers the new study to be valid. From his point of view, Nanotyrannus is a separate species. However, in order to finally clarify the discussion, further fossil discoveries of both Nanotyrannus and young tyrannosaurs are required.

Difficult species definition

Unfortunately, young dinosaurs are extremely rare to find because their bones are softer and decay more quickly. In their conclusion, the two study authors emphasize that despite intensive research and the iconic status of the Tyrannosaurus Rex, many questions still remain unanswered and we know very little about the true biodiversity of dinosaurs.

“We constantly have to ask ourselves whether fossilized bones really belong to a new species of dinosaur or whether they just show different variations or ages,” says Oliver Rauhut from the Bavarian State Collection for Paleontology and Geology. There are regular discussions about whether certain dinosaur species are actually independent species.

In 2010, for example, the equally popular Triceratops was made into a juvenile version of Torosaurus. A theory that has since been refuted. Pachycephalosaurus, a bipedal herbivore with a thick skull plate, may also have had fewer relatives than previously thought. In 2009, US researchers declared its cousins ​​Stygimoloch and Dracorex to be young variants of Pachycephalosaurus. An exciting side note in their study: A third of all named dinosaur species could be such misclassifications and actually represent different developmental stages of already known species.

“We are facing two major challenges. A species definition that is not clear even in animals living today and the limitation to bones. In the case of dinosaurs, genetic differentiation no longer applies, as does the question of the ability to reproduce,” explains Rauhut. Differences in colors or striking skin structures are only known in a few fossils. Researchers are extremely rarely able to identify differences between female and male dinosaurs. And so the discussions about Tyrannosaurus species, which are carried out with a lot of ego and ideology, at least have one good thing: They show the public how limited our idea of ​​true biodiversity really is during the 165 million year rule of the dinosaurs.