T. rex may have had lips like a modern lizard’s

In films and TV reveals, Tyrannosaurus rex usually sports activities a fleet of massive, sharp tooth which might be nearly all the time on show. However the dinosaurs and their kin could have saved their pearly whites largely tucked behind lizardlike lips.

Just like Komodo dragons right this moment, these dinosaurs had ample gentle tissue across the mouth that may have functioned as lips, an evaluation of fossilized and fashionable reptile skulls and tooth finds. The analysis, described within the March 31 Science, challenges frequent, conventional reconstructions of how these prime predators appeared in life.

“It is a good, concise reply to a query that has been requested for a very long time by dinosaur paleontologists,” says Emily Lessner, a vertebrate paleontologist on the Denver Museum of Nature and Science, who wasn’t concerned within the examine. 

Gentle tissue isn’t usually included in analyses of the biomechanics of feeding dinosaurs, she says. Acknowledging the potential presence of lips in these assessments may change how we expect some dinosaurs ate.

It’s “not an unfair argument” to recommend that nonavian theropods, the dinosaur group that features T. rex, might need had their chompers continually uncovered, says paleontologist Thomas Cullen of Auburn College in Alabama. Their sharp tooth tended to be massive, doubtlessly too massive to suit totally within the mouth. And crocodiles and their ilk — theropods’ closest residing family which have tooth — lack lips.

However nearly all land vertebrates right this moment have liplike coverings for his or her tooth, Cullen says. Why ought to Tyrannosaurus and different nonbird theropods be totally different?

Cullen and his colleagues analyzed fossilized theropod skulls and tooth alongside comparisons of residing reptiles. The staff examined the sample of foramina, small passageways via bones, within the higher jaws of theropods and a few fashionable and different extinct reptiles.

Foramina route blood vessels and nerves to the gentle tissue across the mouth. In crocodilians, these foramina are scattered throughout the jaw. However in lipped reptiles like lizards, the little holes are organized in a line alongside the sting of the jaw close to the tooth. Tyrannosaurus shares this row of jaw pores, the evaluation confirmed.

Enamel in theropod and crocodilian tooth additionally yielded clues. When enamel dries out, it wears down extra simply. The researchers discovered that the aspect of alligator tooth which might be regularly uncovered erode greater than the wetter aspect going through the within of the mouth. Theropods have a extra even put on sample, suggesting the tooth have been saved coated and moist. 

And monitor lizards (Varanus spp.), which have proportionally lengthy, serrated tooth very similar to theropods did, don’t lower their lip protection with rising tooth and cranium dimension, the researchers discovered. As a result of tooth size and cranium dimension scale equally in monitor lizards and theropods, the staff says, there’s no purpose to assume that theropods couldn’t match their tooth totally of their mouths too.

What’s extra, the evaluation revealed a neat row of jaw foramina in Hesperosuchus, an extinct, very early cousin of crocodilians. That discovering means that lips could have been current within the earliest archosaurs — the group of reptiles that gave rise to dinosaurs (together with birds) and crocodilians. The researchers assume lips could have finally been misplaced within the crocodilian lineages that survived to the trendy day and misplaced in a separate course of in birds.

However paleontologist Thomas Carr, who has studied tyrannosaurs, isn’t persuaded by the outcomes. The brand new examine “will be summed up in two phrases: utterly unconvincing,” says Carr, of Carthage School in Kenosha, Wisc.

In 2017, he and his colleagues confirmed that tyrannosaurs had a tough, wrinkled floor texture to the jaw bones, and that crocodilians have this similar bone texture underlying the lipless, scaly margins of their jaws (SN: 3/30/17).

“In lots of circumstances,” Carr says, “the gentle tissues depart signatures on bone.” These signatures can inform you what sat on prime of the bone in animals whose pores and skin or scales haven’t been preserved, he says. The brand new analysis “utterly disregards … the feel of the facial bones, which unambiguously reveals that [tyrannosaurs] had flat scales, like in crocodilians, all the best way all the way down to the sides of the jaws.”

This bone roughness isn’t a constant characteristic in theropods, Cullen says. Younger tyrannosaurs and smaller theropod species had clean bones much like a lizard’s. It’s attainable that these animals had lips after which misplaced them over their life, however “I don’t assume there may be actually any fashionable instance of that sort of factor taking place,” he says.

One thing like the invention of a mummified tyrannosaur carcass with preserved facial tissues, Carr says, may settle the matter of who had lips and who didn’t (SN: 10/12/22).