Tyrannosaurus rex bared its huge teeth like a crocodile
The old claim turned out to be wrong and was rejected by evidence.
TaughtPicture T. rex and you picture the teeth: rows of banana-sized daggers jutting out even when the mouth is shut, exposed to the air like a crocodile's. Every model, museum mount, and movie monster agreed.
NowA March 2023 study in Science concluded that T. rex and other big theropods had scaly, lizard-like lips that fully covered their teeth when the mouth was closed. The crocodile-style permanent snarl appears to be wrong.
What actually happened
The researchers, led by Thomas Cullen, tested the exposed-teeth image against evidence and it failed on several fronts. They measured theropod skulls and teeth and found the jaws were tall enough to sheathe even the longest teeth behind lips, the way a Komodo dragon's are. Crocodiles, whose teeth really are exposed, were the wrong model to copy.
A neat second line of evidence came from tooth enamel. Enamel dries out and cracks if a tooth sits exposed to air, as it does in crocodiles, but a Daspletosaurus tooth they examined showed even, well-preserved enamel along its length, the signature of a tooth that stayed moist inside a closed, lipped mouth.
This overturns a specific and very familiar picture rather than the animal itself: T. rex was still an enormous predator with enormous teeth. It just probably kept them behind lips, so a live one at rest would have looked less like a snarling crocodile and more like a giant, scaly-lipped lizard.
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Who was taught this
Still standard through 2023, so anyone who finished school between 1950 and 2023 learned the earlier version.