Dinosaur expert Don Lessem and paleontologist Tim Rowe answer students' questions about Tyrannosaurus rex.


Q: How tall was the T. rex?
A: T. rex was at least 12 feet tall but it didn't stand tall like we do. Instead, it leaned forward with its tail up nearly as high as its lowered head. (Don Lessem)

Q: How much did the T. rex weigh?
A: By most estimates, T. rex weighed at least seven tons. (Don Lessem)

Q: Was it cold-blooded or warm-blooded?
A: I do think T. rex was warm-blooded, though perhaps not as warm-blooded as us. When they were young, they may have grown fast like warm-blooded animals, but relied more on their own body mass to keep them warm later on in their life. (This is a more efficient way of living than our way of burning up a lot of calories all the time to stay warm and active.) (Don Lessem)

Q: How many bones did the T. rex have? More than we do?
A: Since we don't have a whole T. rex, no one knows how many bones it had. But we do have most of it, so we could guess pretty well. I'd guess it didn't have all that many more bones than us, just bigger bones. T. rex had less fingers, only two, but many more bones in its tail. It also had belly ribs, which we don't have, and more teeth (about 50). (Don Lessem)

Q: How many teeth did T. rex have?
A: T. rex had about 50 teeth, as large as 8 inches. Their teeth were sharp enough to saw meat and strong enough to crack bone. It could grow a new tooth in 2 years or less anytime it lost one. (Don Lessem)

Q: Did T. Rex have the sharpest teeth of any animal?
A: Most meat-eaters had grooved teeth like steak knives to saw meat well. T. rex had the biggest teeth, which were so sturdy they could crush bone. But it's hard to say if their teeth were the sharpest. (Don Lessem)

Q: Were the claws of T. rex really as sharp as knives?
A: T. rex's claws were sharp, but not great weapons since its arms were so short they couldn't touch each other. T. rex was about 45 feet long, but its arms were only as long as mine. But they were powerful, capable of lifting 450 pounds. I suspect they may have used them for holding onto a mate (an old theory) or grasping the flesh of a dead dinosaur. T. rex's real weapons were teeth, which were as sharp as steak knives and the size of bananas. (Don Lessem)

Q: How did T. rex sleep? Did it sleep standing up?
A: T. rex probably slept standing up like a horse or sitting on its big pubic boot, a bone in its pelvis. I don't know if it snored, but it probably roared when awake, and one Japanese scientist thinks it sounded like a big belch. It probably had bad breath from eating rotting meat and not brushing between meals! (Don Lessem)

Q: How much food could a T. rex eat in a day?
A: We can't be sure. Big meat-eaters today like lions eat a lot at one time and then might not eat again for a week! T. rex could bite off 500 pounds in one bite! Maybe it ate a few hundred pounds of triceratops one day and then didn't eat again for a while. We'll never know. (Don Lessem)

Q: Do you think T. rex was a predator or a scavenger?
A: It is likely that they were both. Big carnivores today, from lions on down, are inefficient hunters and scavenge more often. It's more energy efficient. There were huge herds of triceratops and duckbills in T. rex time, so plenty of ill, aged, young, and dead to feed upon without much dangerous and draining hunting effort. (Don Lessem)

Q: Did the T. rex pounce on its prey?
A: Scientist believe that T. rex was, like most meat-eaters, a scavenger most of the time. That means it ate mostly animals that were already dead. T. rex could kill most anything it wanted, but it didn't pounce. T. rex weighed seven tons or more — that's kind of heavy to do any jumping, unless you want to land with a broken leg! (Don Lessem)

Q: How do we know that T. rex didn't have hair?
A: Mammals are the only animals that have hair. Since dinosaurs were not mammals, we know there was no hair on T. rex. (Don Lessem)

Q: Do you know if Tyrannosaurus rex always had that name?
A: T. rex wasn't called T. rex by other dinosaurs, but it was the first name given to that animal, in 1905. It was also, mistakenly called dynamosaurus, but the name Tyrannosaurus rex, which means tyrant lizard king, is the one that stuck. (Don Lessem)

Q: Have any eggs been found from T. rex?
A: No, not so far. (Don Lessem)

Q: Is it true that a T. rex can not see you unless you are moving or making sounds? What do we know about T. rex's vision perception?
A: It's probably not true. T. rex had large visual lobes in its brain to process information for sight, and a very large area in its brain for smell information. Its skull was wide enough for both eyes to focus on the same object, giving it good depth perception. (Don Lessem)

Q: Could an allosaurus kill and eat a T. rex?
A: T. rex lived 65 million years ago and allosaurus 145 million years ago. It would have been a bloody battle, but T. rex would have won easily. It is bigger, with far more powerful jaws, and is more agile. Even though it had such runty arms and one less finger than allosaurus, T. rex could still bite allosaurus to death. (Don Lessem)

Q: What is the difference between allosaurus and Tyrannosaurus rex?
A: Tyrannosaurus and allosaurus are both carnivorous dinosaurs known as theropods. Allosaurus is much older, occurring in late Jurassic rocks, while Tyrannosaurs is two to three times as large and occurs in the late Cretaceous rocks (about 80 million years younger). Allosaurus is primitive, with a relatively long hand with three fingers, whereas Tyrannosaurus has a reduced hand with only two functional fingers. There are a lot of subtle differences in the head, backbone and ankle that suggest Tyrannosaurus is more closely related to modern birds than allosaurus. This is a question that a lot of paleontologists have been thinking about and working on in the last 3 or 4 years. (Tim Rowe)

Q: Is there a dinosaur that can kill a T. rex ?
A: I don't think anything killed a T. rex except another T. rex. (We found a T. rex with a broken off tooth from another T. rex stuck in its cheek. A pack of Utahraptors might have been big enough, even though each is half T. rex's size. But Utahraptors were mean enough to have killed a T. rex if they had lived at the same time. (Don Lessem)

Q: Who usually won in battle, tricerotops or T. rex?
A: I imagine T. rex could have beaten triceratops any time, since triceratops horns weren't really positioned or designed to do much damage, frightening as they looked. Plus, T. rex was stronger and faster. But it probably wasn't worth T. rex's energy to chase live triceratops when there were so many dead and dying in the herds that lived in its time. I think T. rex was mostly a garbage truck, eating like a vulture. (Don Lessem)

Q: Which dinosaur was the strongest?
A: The strongest dinosaur was probably the biggest, the six-story high ultrasauros. But among meat-eaters, T. rex was the strongest. (Don Lessem)

Q: How big was a T. rex heart compared to ours?
A: Since soft parts like hearts don't fossilize, it's all guess work, but if T. rex was reasonably warm-blooded, as many suggest, its heart might be 140 times the size of yours. After all if you weigh 100 pounds, T. rex is that much bigger than you. Your heart is the size of a fist so T. rex's heart might be about the size of you. (Don Lessem)

Q: How did T. rex sneak up on its prey if it was so big?
A: I don't think it sneaked up on its prey. Since it weighed seven tons it was pretty hard to hide. (Don Lessem)

Q: How long is a T. rex's foot?
A: We have only found one footprint of the T. rex, which was about two feet or more wide. (Don Lessem)

Q: How do we know that the Tyrannosaurus rex was the meanest dinosaur?
A: T. rex may not have been the meanest; he might just have been a garbage eater, or scavenger. We don't know. But we do know he had the strongest jaws and the biggest teeth of any meat-eater and he was the biggest, so we guess that he might have been the meanest. One scientist says Utahraptor was meaner, even though it was just 20 feet long. It had huge claws on its toes and fingers, weapons T. rex didn't have. (Don Lessem)

Q: How much could a Tyrannosaurus rex tooth weigh?
A: T. rex teeth now weigh about a pound or two, but they've been fossilized, filled in with rock. In real life they probably weighed less. Teeth aren't so heavy. (Don Lessem)