In films and television programs, Tyrannosaurus rex frequently sports a fleet of huge, sharp teeth that are almost constantly on screen. But the dinosaurs and their kin might have kept their teeths mainly tucked behind lizardlike lips.
Similar to Komodo dragons today, these dinosaurs had sufficient soft tissue around the mouth that would have operated as lips, an analysis of fossilized and modern-day reptile skulls and teeth discovers. The research study, explained in the March 31 Science, challenges typical, standard restorations of how these leading 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 associated with the research study.
Soft tissue is rarely consisted of in analyses of the biomechanics of feeding dinosaurs, she says. Acknowledging the possible existence of lips in these tests might alter how we believe some dinosaurs consumed.
It’s “not an unfair argument” to recommend that nonavian theropods, the dinosaur group that consists of T. rex, may have had their chompers continuously exposed, says paleontologist Thomas Cullen of Auburn University in Alabama. Their sharp teeth tended to be big, possibly too huge to fit completely in the mouth. And crocodiles and their ilk — theropods’ closest living family members that have teeth — do not have lips.
But almost all land vertebrates today have liplike coverings for their teeth, Cullen says. Why should Tyrannosaurus and other nonbird theropods be various?
Cullen and his coworkers evaluated fossilized theropod skulls and teeth along with contrasts of living reptiles. The group analyzed the pattern of foramina, little passages through bones, in the upper jaws of theropods and some modern-day and other extinct reptiles.
Foramina path capillary and nerves to the soft tissue around the mouth. In crocodilians, these foramina are spread throughout the jaw. But in lipped reptiles like lizards, the little holes are organized in a line along the edge of the jaw near the teeth. Tyrannosaurus shares this row of jaw pores, the analysis revealed.
Enamel in theropod and crocodilian teeth likewise yielded ideas. When enamel dries, it uses down more quickly. The scientists discovered that the side of alligator teeth that are continuously exposed deteriorate more than the wetter side dealing with the within the mouth. Theropods have a more even use pattern, recommending the teeth were kept covered and damp.
And screen lizards (Varanus spp.), which have proportionally long, serrated teeth similar to theropods did, don’t reduce their lip protection with increasing tooth and skull size, the scientists discovered. Because tooth length and skull size scale likewise in screen lizards and theropods, the group says, there’s no factor to believe that theropods couldn’t fit their teeth completely in their mouths too.
What’s more, the analysis revealed a cool row of jaw foramina in Hesperosuchus, an extinct, extremely early cousin of crocodilians. That finding recommends that lips might have existed in the earliest archosaurs — the group of reptiles that generated dinosaurs (consisting of birds) and crocodilians. The scientists believe lips might have become lost in the crocodilian family trees that made it through to the modern and lost in a different procedure in birds.
But paleontologist Thomas Carr, who has actually studied tyrannosaurs, is not convinced by the outcomes. The brand-new research study “can be summed up in two words: completely unconvincing,” says Carr, of Carthage College in Kenosha, Wisc.
In 2017, he and his coworkers revealed that tyrannosaurs had a rough, old and wrinkly surface area texture to the jaw bones, which crocodilians have this exact same bone texture underlying the lipless, flaky margins of their jaws (SN: 3/30/17).
“In many cases,” Carr says, “the soft tissues leave signatures on bone.” Those signatures can inform you what sat on top of the bone in animals whose skin or scales haven’t been maintained, he says. The brand-new research study “completely disregards … the texture of the facial bones, which unambiguously shows that [tyrannosaurs] had flat scales, like in crocodilians, all the way down to the edges of the jaws.”
This bone roughness isn’t a constant function in theropods, Cullen says. Young tyrannosaurs and smaller sized theropod types had smooth bones comparable to a lizard’s. It’s possible that these animals had lips and after that lost them over their life, however “I don’t think there is really any modern example of that kind of thing happening,” he says.
Something like the discovery of a mummified tyrannosaur carcass with maintained facial tissues, Carr says, might settle the matter of who had lips and who didn’t (SN: 10/12/22).
