In movies and TV shows, Tyrannosaurus rex often sports a fleet of big, sharp teeth that are almost always on display. But the dinosaurs and their kin may have kept their pearly whites mostly tucked behind lizardlike lips.
Similar to Komodo dragons today, these dinosaurs had ample soft tissue around the mouth that would have functioned as lips, an analysis of fossilized and modern reptile skulls and teeth finds. The research, described in the March 31 Science, challenges common, traditional reconstructions of how these top predators appeared in life.
“This is a nice, concise answer to a question that has been asked for a long time by dinosaur paleontologists,” says Emily Lessner, a vertebrate paleontologist at the Denver Museum of Nature and Science, who wasn’t involved in the study.
Soft tissue is not often included in analyses of the biomechanics of feeding dinosaurs, she says. Acknowledging the potential presence of lips in these tests could change how we think some dinosaurs ate.
It’s “not an unfair argument” to suggest that nonavian theropods, the dinosaur group that includes T. rex, might have had their chompers constantly exposed, says paleontologist Thomas Cullen of Auburn University in Alabama. Their sharp teeth tended to be large, potentially too big to fit fully in the mouth. And crocodiles and their ilk — theropods’ closest living relatives that have teeth — lack lips.
But almost all land vertebrates today have liplike coverings for their teeth, Cullen says. Why should Tyrannosaurus and other nonbird theropods be different?
Cullen and his colleagues analyzed fossilized theropod skulls and teeth alongside comparisons of living reptiles. The team examined the pattern of foramina, small passageways through bones, in the upper jaws of theropods and some modern and other extinct reptiles.
Foramina route blood vessels and nerves to the soft tissue around the mouth. In crocodilians, these foramina are…
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