T. rex—hunter or scavenger? In this day and age of social freedoms, why not choose both? Because studying dinosaurs, especially fierce, glamorous ones like Tyrannosaurus rex, leads to fame and—well, if not fortune, then at least movie deals.

A study published this week in the Proceedings of the National Academy of Sciences determines, due to dental data, that T. rex was definitely a hunter.

In the Hell Creek Formation of South Dakota, researchers discovered a fossilized spine of a plant-eating hadrosaur that had an odd bone growth. Examining the fossil with a CT scan, the researchers found a tooth—belonging to a T. rex—within the bone. In fact, the bone had grown around the tooth.

“Lo and behold, the tooth plotted out just exactly with T. rex—the only known large theropod from the Hell Creek formation,” exclaims study author David Burnham of the University of Kansas. “We knew we had a T. rex tooth in the tail of a hadrosaur. Better yet, we knew the hadrosaur got away because the bone had begun to heal. Quite possibly it was being pursued by the T. rex when it was bitten. It was going in the right direction—away. The hadrosaur escaped by some stroke of luck.”

T. rex teeth had previously been found in the fossilized bones of a young ceratopsian (Triceratops or one of its kin), but there was no evidence to conclude whether the ceratopsian was alive or dead when the T. rex made a snack of it. The hadrosaur’s escape provides evidence that T. rex was a dangerous, if not always accurate, predator, according to the study’s authors.

Because T. rex regularly shed its teeth, the dinosaur went away hungry, but otherwise no worse for the encounter. It would have grown a new tooth to replace the one left behind in the hadrosaur’s tail. This could have been a typical example of T. rex’s hunting efforts, even if it didn’t result in a meal.

But the story doesn’t end there. Just because you hunt doesn’t mean that’s how you find all your meals, and most scientists agree that T. rex was likely an opportunistic scavenger, too. In fact, researchers and science writers that focus on dinosaurs are tired of the either-or question. “Whether or not T. rex hunted is the most-asked question I get at talks and on the radio. And that makes me sad,” tweeted Brian Switek Monday in response to this study. There are so many more exciting questions in the field, posted paleontologist John Hutchinson, in his blog response to the publication.

So we’ll put it to rest here… T. rex: hunter and scavenger.

Illustration by Robert DePalma II

Almost a year has passed since crane operator Brandon Valasik discovered a Columbian mammoth (Mammuthus columbi) tooth at the Transbay Transit Center. When the find was donated to the Academy, Peter Roopnarine, curator of Invertebrate Zoology and Geology, told Science Today, “If we’re able to put the recent find on display, it will be a great opportunity to tell the story of the recent fossil history of San Francisco.”

The Academy has seized that opportunity. On a daily basis, Naturalist Center staff point out the tooth and talk about the ice age animals that roamed the area where San Francisco now stands. Visitors express astonishment that these real giants walked on this very spot.

“Wow!” “No way!” “Here, in San Francisco?” “You’re kidding!” “That’s incredible!” “Cool!” “Awesome!” To quote a few responses…

And this awesome discovery might enable more paleontological finds. A number of workers from different Bay Area construction sites have come to the Academy just to see the tooth. They said they wanted to see what it looks like up close and personal so they know how to recognize another one if it turns up on the job. Visitors marvel that a construction worker spotted the tooth and “didn’t mistake it for just another rock.” Many are thrilled to learn that other workers have come to see it so they can be on the lookout at their construction sites.

The wonder and pride extend to the Transbay Transit Center. Recently, the Senior Geotechnical Engineer at the site came in to show the tooth to some friends. He boasted, “I was the third person to ever hold the tooth, and I set it aside in a box for safe keeping for the paleontologist!”

A member of the Academy’s PR department shared that a Transbay Joint Powers Authority employee called and inquired, “Can you confirm if the mammoth tooth is still on display? We have members of the community inquiring.” And just this week, Transbay staff was hard at work, installing a display of the Center’s human-made found objects in their lobby at 201 Mission Street. In doing so, a staff member called the Academy’s Geology Research department to request photos because they plan to display a banner that features the tooth at the Academy. (Click here to see their exhibit.)

So yes… cool! And incredible! And awesome! It’s a foot-long piece of dentition once strong enough to grind up 320 kg (700 lbs) of vegetation a day for an animal weighing eight metric tons (18,000 lbs) that 11,000 years later retains a powerful hold on our imagination.

Additional ice age fossils wowing visitors in the Naturalist Center include a saber-toothed cat partial lower jaw with teeth, an American mastodon partial lower jaw with teeth, and a dire wolf skull. The latter item has numerous visitors asking, “Dire wolves really exist? They’re not just on Game of Thrones?”

The Naturalist Center features two other items of note from the Academy’s Geology Research collections: a 1.07-meter (3.5-foot) sauropod (herbivorous dinosaur) leg bone which visitors love to touch and a 20-centimeter (eight-inch) round sauropod coprolite (fossilized poop). The typical reaction from the coprolite’s biggest fans—groups of five- to seven-year-old boys—is an instantaneous holding of noses, squinting of eyes, and a collective shout of “Ewwwwww!” because, after all, why wouldn’t it still be stinky after 150 million years?

As always, the educational opportunities in the Naturalist Center are endless.

Nan Sincero is a naturalist and Program Lead in the Academy’s Naturalist Center.

Imagine losing and regrowing teeth every year. You might feel less guilty when you forget to floss. Indeed, most vertebrates experience such guilt-free existence because, unlike humans, they can replace teeth throughout their lives. (No wonder there’s no call for dentists in the animal world!)

“Humans naturally only have two sets of teeth—baby teeth and adult teeth,” says Dr. Cheng-Ming Chuong, director of the Laboratory of Tissue Development and Regeneration at the University of Southern California (USC). “Ultimately, we want to identify stem cells that can be used as a resource to stimulate tooth renewal in adult humans who have lost teeth. But, to do that, we must first understand how they renew in other animals and why they stop in people.”

To understand how teeth regenerate in other animals, Chuong and his colleagues looked to a very toothy vertebrate—the American alligator. Alligators have well-organized teeth with similar form and structure as mammalian teeth and are capable of lifelong tooth renewal. “They have 80 teeth, each of which can be replaced up to 50 times over their lifetime, making them the ideal model for comparison to human teeth,” explains Dr. Ping Wu, who collaborates with Dr. Chuong at USC.

Using microscopic imaging techniques, the researchers found that each alligator tooth is a complex unit of three components—a functional tooth, a replacement tooth, and the dental lamina (the band of tissue crucial to tooth development). The tooth units are structured to enable a smooth transition from dislodgement of the old tooth to replacement with the new tooth. The researchers identified that new replacement teeth develop from stem cells within the alligator dental laminae.

“In the future, we hope to isolate those cells from the dental lamina to see whether we can use them to regenerate teeth in the lab,” says another USC researcher, Randall B. Widelitz. The scientists hope to use this research to stimulate tooth regeneration in people with missing choppers.

The study is published this week in the Proceedings of the National Academy of Sciences.

Image: David R. Tribble/Wikipedia