Are T. rex’s terrifying teeth just a Hollywood myth?

Close your eyes and picture a Tyrannosaurus rex. What do you see? Probably some version of the infamous "Jurassic Park" monster, or maybe Sue, nonbinary icon and one of the most complete fossil sets in history. Either way, the first thing you see is, of course, the teeth. Nearly every modern depiction of the T. rex features its massive set of razor-sharp teeth on full display. But a recent study raises the question: What if their signature snarl was a work of fiction? New evidence suggests that the iconic beast’s teeth would have been covered by a set of scaly lips.

Until recently, most paleontologists agreed that T. rex’s teeth would protrude from its mouth, due to both the sheer size of the teeth and the species’ evolutionary similarities to crocodiles. Some even believed that T. rex wouldn’t have been able to fully close its mouth due to the size of those teeth. It was previously theorized that, due to certain similarities with the crocodile, their teeth would similarly point outside the mouth when closed. However, new research casts doubt on these claims, and brings to light plenty of evidence to the contrary.

Science recently published a study on facial reconstruction in theropods. AKA, it looked at the way the facial features may have been constructed in a certain class of dinosaurs. Several species in particular were addressed, including T. rex. The study questioned the belief that dinosaurs had crocodile-like teeth, using evidence from wear and tear patterns in fossils as well as looking at the tooth-to-skull size ratios of several species.

The researchers found that when compared to the mouths of modern-day reptiles, T. rex’s teeth are actually quite reasonable. In fact, by proportion, modern-day Varanus salvadorii (crocodile monitor lizards) have even larger teeth than the famous carnivore (despite the name, they are not closely related to crocodiles). Varanus komodoensis (komodo dragons) also have relatively large teeth, and like crocodile monitors, they have a set of scaly lips which allows them to fully close their mouths with ease, concealing most of their teeth from view even when the mouth is fully open.

Additionally, the study observed key differences between crocodile and dinosaur tooth structure. In a crocodile, the teeth are on a slight outward angle from the jaw, causing them to protrude from their closed mouth. In a T. rex, the teeth face straight upward, suggesting that they would fit neatly within the mouth. The second structural difference had to do with tooth enamel. Since a crocodile’s teeth are constantly exposed to the elements, they show clear signs of wear on the outside of the tooth. But when closely examined, the T. rex’s teeth showed no such wear. This led the researchers to theorize that, like the komodo dragon, the T. rex had a set of scaly lips covering its teeth. If you’re having trouble imagining what that may have looked like, picture the middle stages of an Animorph between an iguana and the dragon from Shrek.

It should be said, at this point, that the reason I’m talking about lizards so much is because they’re most likely the best living reference point for how dinosaurs may have looked, particularly for theropods. Theropods are a group of two-legged dinosaurs that belonged to one of the major dinosaur lineages Saurichia, which means “lizard-hipped.” As the name would suggest, this is because these dinosaurs’ hips are remarkably similar in structure to those of lizards. From this, we can gather that the best modern reference point for much of dinosaur biology would be large lizards.

Now you may have heard that chickens or ostriches are the direct descendants of T. rexes, which is true — birds and reptiles actually have a common ancestor in certain carnivorous dinosaurs. But birds evolved tens of millions of years after the last dinosaur roamed the earth, and took an evolutionary path that means they’re much less similar physically. There are a few similarities, though, including that theropods all had bird-like hollow bones. On a related note, you may have also heard speculation that T. rexes were covered in feathers. This was most likely not the case, despite what its genetics eventually led to. Despite some T. rex ancestors having feathers themselves, many skin impressions have been analyzed and no trace of feathers have been found.

The question of T. rex lips leads to other interesting questions, because broadly speaking, we actually have no idea what dinosaurs looked like in real life. Sure, paleontologists know their skeletal structures and have some imprints of skin texture, but things like soft tissue disintegrate completely over time, leaving us largely in the dark about what exactly they looked like while they were alive. Because bodily features like fatty deposits or skin flaps are almost never preserved, this has an undeniable effect on how we model the supposed appearance of dinosaurs we’ve discovered. Without access to the bulk of their soft tissue, we just make educated guesses at how they were proportioned. This leaves us with the skin-and-bones, gaunt-looking dinosaurs we depict today — the artistic process, essentially, is to model the skeleton, add muscles over it, and then shrink-wrap some skin around that. But when we look at the animals around us, almost none of them are actually built like that! Even reptiles carry fatty deposits, especially the larger ones. Basically, the dinosaurs we depict look like the emaciated, abandoned pets from a Humane Society commercial.

The complete lack of soft tissue remains leads to very conservative depictions of what dinosaurs and other prehistoric creatures would have looked like, because paleontologists are understandably hesitant to speculate with such little evidence. In this way, we may have no idea what certain dinosaurs actually looked like. To illustrate this point, paleoartists C. M. Kosemen and John Conway collaborated on a series of drawings imagining what modern-day animals would look like if we drew them the way we draw dinosaurs — based on nothing but the skeleton. The result is… well… slightly haunting, but a great illustration of how wrong we may be about dinosaurs. If we would have thought zebras looked like that, how much could we be missing about dinosaurs?

But sparing some miraculous scientific advances, the best we can do for now is combine what hard evidence we have with what we know about similar modern-day animals. So throw out that Jurassic Park poster, and instead imagine the biggest komodo dragon the world has ever seen.