Meet Chilesaurus, a New Raptor-Like Dinosaur With a Vegetarian Diet

For decades, the word “theropod” was synonymous with “meat-eating dinosaur”. Their ranks included such illustrious carnivores as Tyrannosaurus, Velociraptor, Spinosaurus and many others that have yet to star in the Jurassic Park franchise. But over the past several decades, as paleontologists have chipped away at the fossilized pile of dinosaurs waiting to be studied, they have uncovered a slew of theropods that preferred plants to flesh.

Today, researchers can add an unusual South American find to the list. The new Jurassic dinosaur wasn’t discovered by a paleontologist, but by a seven-year-old child. On February 4, 2004, while hiking around southern Chile with his geologist parents Manuel Suarez and Rita de la Cruz, young Diego Suarez picked up a few bones he found on a hillside. His parents immediately recognized them as a rib and vertebra of a little dinosaur, and, with his sister Macarena joining in, Diego and his family scoured the site for more.

Now, more than a decade later, the dinosaur has been named for Diego and the place it was found: Chilesaurus diegosuarezi. Based on several specimens unearthed at the site, Fernando Novas of the Museo Argentino de Ciencias Naturales and his co-authors announced the new plant-plucking theropod this week in Nature.

The dinosaur looks like it’d be more at home at the Mos Eisley Cantina than running around Jurassic floodplains. Balanced on two legs, Chilesaurus has three thick, short fingers but only two claws, and the dinosaur’s blunt, rounded skull was set with short, leaf-shaped teeth. This combination of features, Novas says, give the dinosaur away as “a strict plant eater.”

The switch from carnivorous to herbivorous habits didn’t just happen once among dinosaurs. Species of the toothless, ostrich-like ornithomimids, the parrot-esque oviraptorosaurs and the tubby, long-necked therizinosaurs all developed more omnivorous, if not fully herbivorous, lifestyles independently of each other during the Cretaceous, which started about 145 million years ago. And that’s not to mention that some of today’s dinosaurs—birds—are herbivores, too.

There were even older plant-munching theropods. In 2009, Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and colleagues described a 150-million-year-old turkey-sized theropod they called Limusaurus. The little dinosaur’s beak suggests that it was pecking at fern fronds rather than chasing down prey. When it was named, Limusaurus was the earliest herbivorous theropod known. Now, at around 150 million years old, Chilesaurus is also a contender for that title.

What led the ancestors of Chilesaurus down the evolutionary road to the salad bar isn’t yet clear, but what’s immediately apparent is that this dinosaur was an important part of its ancient ecosystem. In the place where Diego discovered it, there are more bones of Chilesaurus than any other creature. This is odd. In most environments of about the same age, the most common dinosaurs are beaky little herbivores that belonged to a very different lineage of dinosaurs called ornithischians. Here, for some reason, a theropod came to dominate instead.

“The discovery of Chilesarus not only challenges our conception of theropod evolution, but also about the ecological role it played,” Novas says. It’s certainly a very different image than that of the enormous, rapacious theropods that usually roar through books and loom over museum halls. And if Chilesaurus had some sort of protofeather or fluff—as many theropods have been found to possess—than it may even have been a theropod you'd want to snuggle.

“This is a really unusual beastie, a bit of a dinosaur Frankenstein,” says paleontologist Lindsay Zanno of the North Carolina Museum of Natural Sciences. But Chilesaurus is much more than an oddball. “If Chilesaurus’s proposed place in the theropod family tree holds up to additional scrutiny, then we have at least three and up to seven instances of theropods adapting to some form of a plant-based diet, one of which may be linked to the origin of the only surviving group of theropod dinosaurs, birds,” Zanno says. Why this happened so many times is not yet clear, but for now, Zanno notes that Chilesaurus is a potent reminder of an evolutionary truism: “If given new opportunities to succeed, life will find a way.”

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.