We all know Tyrannosaurus rex. It is perhaps the most iconic dinosaur out there and a favorite of most dinosaur fans. And for good reason: T-Rex looks completely badass.
The T-Rex we all know and love today looks very different from what we once believed it to be. Early paleontologists depicted the tyrannosaur as a giant, upright scaly lizard. It was a slow, clumsy animal that took heavy thundering steps as it walked, its scaly tail dragging along the ground behind it. Its tiny arms, too small and weak to do much of anything, dangled uselessly. And yet, even then, we still saw the tyrannosaurus as a dangerous, capable predator and it took the world by storm.
We've learned a lot from the nearly 50 T-Rex fossils we have recovered over the years, greatly changing how we see the majestic dinosaur. We now know it held itself horizontally, moving gracefully with its tail held up from the ground. Its large, bird-like legs made it capable of running at great speeds to capture prey. It had quality senses, including very good sight (they could most definitely see their prey even if it was standing still!), similar to many birds today. Even its tiny arms have gotten a better reputation; despite their small size, they were well muscled and very powerful, likely used to push off the ground when the T-Rex stood up. Instead of scales, it likely sported feathers, or even a furry down, for part or all of its life. Thanks to all our discoveries, we have a far more accurate idea of what T-Rex really looked like, as reflected in recent pop culture hits (you know where this is going...).
Robert Reisz, a paleontologist at the University of Toronto, still believe there is a discrepancy in the appearance of the tyrannosaur's head. Rather than constantly bearing its teeth (extending outside their mouths and fully visible whether their jaws were open or closed), Reisz has hypothesize that the T-Rex's teeth (and those of other therapods) were hidden behind scaly lips.
We know for a fact that the T-Rex's teeth had enamel, just like our own.
"The hard enamel of animals' teeth has low water content, and is typically kept hydrated by saliva. Without lips to keep moisture in and prevent the teeth from drying out, the tough enamel would become brittle and more prone to damage and wear." -Robert Reisz Source
Reisz pointed out that some reptilian species, such as crocodiles, do have teeth bared without any kind of lip structure, however these are aquatic animals that spend a great deal of their time in the water. Their environment would protect their teeth from drying out, effectively negating the need for lips. Land-dwelling therapods would likely have needed a lip-like structure to trap moisture due to their perpetual exposure.
Questions have been raised regarding other species with exposed teeth, such as elephants and now-extinct sabre-tooth cats. Without lips to protect their teeth, why don't they face the same damage? Zhijie Jack Tseng, a paleontologist who studies bite-force biomechanics in extinct carnivores at the American Museum of Natural History (NYC), points out that mammalian teeth are very different from reptilian teeth.
"Mammalian teeth are prismatic — they have a crisscrossing structure. When mammal teeth grow, the enamel emerges from the root area and 'races outward in all directions,' creating a 3D shape that may be better at keeping water inside. In reptile teeth, the enamel grows in one direction, creating a different type of structure that may not retain water as effectively — potentially making their teeth more likely to chip or crack." -Zhijie Jack Tseng Source
But Tseng does make one observation that could potentially challenge the lip hypothesis: for reptiles (and dinosaurs), teeth are easily replaceable, and not as big of a deal if lost or broken as it would be in mammalian species. It is entirely possible that T-Rex simply shed teeth as the enamel became damaged.
"Each tooth — relatively speaking — doesn't have as much value to the animal as in mammals. T. rex could chip a tooth or get one stuck in prey, and just replace it. Evolving protection for teeth is not a critical component of how they eat." -Zhijie Jack Tseng Source
We still can't conclusively say that the T-Rex did or did not have lips but this is a fascinating study none-the-less. It just goes to show that even with all the advancements being made, there are still discoveries that challenge our typical view of these lost animals. We may never know EXACTLY how they looked, but we are definitely getting closer. Look at the image of T-Rex from just a few decades ago and how far he has come. What will he look like in another 20 years?
