What did ancient animals REALLY eat?

VO: T-rex: fearsome carnivore. Triceratops: slow-moving herbivore. I’ve never eaten dinner with a dinosaur before. So how do we know what ancient animals ate? Paleontologists have traditionally looked at a number of factors to determine an ancient animal’s diet. Recently, though, a new discovery has disrupted long-held assumptions. Enter the Longipteryx. Jingmai: So it’s a small bird about the size of a blue jay and it has a really long snout or a long beak. And then what's really weird about it is right at the tip of its beak, it has these really large recurved teeth. VO: Since these sharp teeth look perfect for eating meat, paleontologists have long classified Longipteryx as a carnivore. But the teeth weren’t telling the whole story. Recently, researchers found seeds in the stomachs of two Longipteryx specimens—making the case that these early birds were actually herbivores. Jingmai: Understanding diet in extinct animals is super important because it's actually trying to directly document how this organism, in this case, Longipteryx, is interacting with other organisms, whether fish that it's catching or, as we now know, fruits that it's eating, right? So paleontologists always really want to understand diet in extinct animals so that we can understand how these different animals are linked and different organisms are linked to each other within an ecosystem. VO: This isn’t just big news for the Longipteryx. It could impact how paleontologists make conclusions about all the fossils they study. Jingmai: But what’s really exciting is that it kind of says that like all these morphological proxies, these indicators that paleontologists use to try to think what an animal is doing like teeth that are recurved and have serrated margins, those are the teeth of a carnivore. So you look at that, you know, and we're like, it's eating meat and specifically people guessed fish. But now we have evidence that this bird is not doing any of those things. It's actually an herbivore. It's eating fruits. So it's important not just for us to better understand Longipteryx, but also for us to kind of rethink how we make hypotheses about extinct animal behavior based on different structures that we see, that we need to use more caution when interpreting those structures in different ways. VO: So what did the Longipteryx use its teeth for, if not tearing into a fish dinner? Researchers think they may have been perfect for high-stakes food fights. That fruit must have been delicious!