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Did the T. Rex Have Lips?

Scientists think the T. rex had lips that covered its teeth when its mouth was closed.

A T. rex chases an ostrich dinosaur.

© Dr. Mark P. Witton

What’s the scariest thing about a Tyrannosaurus rex? Probably its gigantic teeth! But a group of scientists say they don’t think the T. rex’s teeth could always be seen. They found evidence that the T. rex had lips that covered its teeth.

Scientists studied the teeth of a Daspletosaurus, a dinosaur that was related to the T. rex. They found that the teeth were in pretty good shape. They hadn’t rotted very much. This suggests that the Daspletosaurus was able to cover its teeth when its mouth was closed, keeping the teeth from dry air that can damage them. Since Daspletosaurus and T. rex were similar in many ways, scientists now believe that both types of dinosaurs had lips.

A T. rex skull, a T. rex head with teeth exposed, and a T. rex head with lips covering its teeth.

© Dr. Mark P. Witton

Scientists used to think that the T. rex’s teeth could always be seen. Now, they think the T. rex had lips that covered its teeth, as shown in the bottom picture.

Before this study, scientists thought that T. rex teeth could be seen all the time, like a crocodile’s teeth. This is how T. rex is shown in many illustrations and movies. Why did scientists believe this? T. rex teeth could be up to 6 inches (15 centimeters) long. It was hard to believe that an animal with such big teeth could close its mouth. But now, scientists think the lips were necessary because they allowed the T. rex to keep its teeth healthy. And it needed its teeth to kill its prey!

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Fun Fact

Closeup of a crocodile resting on the surface of water with talk bubble saying the tooth fairy and I are besties.

© Adogslifephoto/

Over time, crocodile teeth wear down and eventually fall out. Luckily, crocodiles can always grow new teeth. A crocodile can go through thousands of teeth in its lifetime!

How Fossils Form

A large part of a dinosaur skeleton embedded in the side of rock.

© o1559kip/

The dinosaurs died out long before humans evolved. We know dinosaurs existed because of the fossils they left behind. Fossils are the remains or molds of life that have been preserved in rock. They’re usually the hard body parts, such as bone, teeth, or shells. Plants can also be fossilized.

How are fossils of animal bones made? 

  1. An animal, such as a dinosaur, dies and is buried in mud. Sometimes the animal sinks into the mud. Other times, it is covered slowly by bits of material brought over by wind or water.

  2. The bones of the animal are protected by the mud. Over time, the bones sink deeper and deeper, and more material covers them. Minerals fill the empty spaces in the bones.

  3. Over millions of years, the mud turns to rock, holding the fossils inside. When the rock is broken, the fossils are revealed.

Looking Sharp!

Closeup of a dinosaur’s skull.

© DavidHCoder—E+/Getty Images

T. rex teeth were serrated—full of small points, like a saw. Can you guess what the T. rex ate? 

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Word of the Day


Part of speech:



: having a row of small points or teeth along the side like a saw

Definitions provided by
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Can you figure out where the words go?


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