Hybrid Dinosaur May Change How We Understand Dinosaur Evolution

The mysterious Chilesaurus—the dino with the seemingly mismatched features—finally has a home on the family tree.

The dinosaur confused paleontologists at first. Its bird-like hips and flat teeth are reminiscent of Stegasaurus, but its head, arms, and legs are more similar to Velociraptor. Paleontologists originally put the kangaroo-sized creature in the same suborder as Velociraptor. But now, paleontologists are recognizing it as a link between dinosaurs like the T. rex and others like Triceratops. The findings, released this week in the Royal Society journal Biology Letters, may change our understanding of dinosaur evolution.

Artistic rendering of the puzzling Chilesaurus.

Here’s Pallab Ghosh, interviewing Barron for the BBC:

“We had absolutely no idea how the ornithischian body plan started to develop because they look so different to all the other dinosaurs. They have so many unusual features,” the Cambridge scientist said.

“In the 130 years since the ornithischian group was first recognised, we have never had any concept of how the first ones could have looked until now.”

Ornithischians, like Triceratops and Stegasaurus, were long considered a monolithic branch on the dinosaur family tree, while saurischians were thought to include two branches, theropods—like T. rex and Velociraptor—and sauropods—like Brachiosaurus.

But in March, Matthew Baron of Cambridge University and his colleagues published findings in Nature that challenged long-standing assumptions. By examining the features of Chilesaurus that overlapped with members of both the theropod and ornithician dinos, the researchers realized that the newly discovered species bridged the carnivorous and herbivorous saurichians. Their analysis resulted in moving theropods from Saurischia and into a class of bird-limbed dinosaurs now known as Ornithoscelida (which formerly contained ornithischians like Triceratops).

Chilesaurus gave the scientists evidence to rethink dinosaur classification, providing a link between theropods and ornithischians.

Chilesaurus lived during the late Jurassic period, around 150 million years ago, in what is now Chile. It stood at about seven to ten feet tall. The specimen was discovered in 2004 by seven-year-old Diego Suarez on a hike with his parents (who happened to be geologists), leading to its moniker of Chilesaurus diegosuarezi.

Baron and his team analyzed over 450 characteristics of dinosaurs and compared existing species to the perplexing hodgepodge Chilesaurus fossil. By noting feature-by-feature similarities, they reevaluated the family tree and concluded that the new dinosaur may bridge the Triceratops branch with the T. rex branch.

Understanding where Chilesaurus sits in dinosaur lineage has apparently taught Baron and his colleagues a lot about dinosaur evolution. The species may be one of the first to consume plants for sustenance, for example. Scientists have long wondered how this transition occurred, and whether herbivorous dinosaurs first developed the beaks used to graze on plants or the stomachs needed to digest them. The Chilesaurus‘s bird-like hips indicates that the gut led the way.

By reorganizing the dinosaur tree, paleontologists have also added further evidence that birds are indeed dino descendants: previously, the theropods we view as birds’ ancestors were not considered relatives of the bird-limbed group, but with the new evidence—and reorganization—they’re all on the same part of the family tree.