Weird Dinosaur Is Missing Link Between T-rex and Giant Herbivores, Paleontologists Say

At first paleontologists thought the Chilesaurus was an ornithischian, like velociraptor, now realize it was an early plant-eating theropod

Reconstructed skeleton of Chilesaurus diegosuarezi
Machairo, Wikimedia Commons

The velociraptor lookalike leaps with slavering jaws, terrifying if slightly ridiculous as it waves its little arms at you, and grabs your carrot. Screams, crunching. Cellulose flies in all directions. "Cut!" George Lucas Jr. screams.

Sound wrong? A strange dinosaur named hilesaurus, because it was found in Chile, would have fit the bill. It is the missing link between T-rex and other bipedal theropods so beloved of gore flick directors, and the giants of herbivorehood, surmise scientists, after spending years puzzling over the bizarre remains before reaching that postulation.

Chilesaurus diegosuarezi has been known since 2015. The problem was figuring out what the remains were of, because the late-Jurassic animal, which lived about 150 million years ago, was bizarre. It had the head-shape and hips of a "vicious" meat-eater but its teeth were clearly those of a "gentle" plant eater. Think, like a fish with feathers.

Initially the paleo set assumed chilesaurus, originally discovered by Fernando Novas, belonged to the Theropoda, the 'lizard-hipped' group of dinosaurs (some of whom would evolve into today's birds). They therefore assumed that its various ornithischian characteristics were a case of convergent evolution. Now they believe the Chilesaurus should be classified with the "bird-hipped" ornithischian dinosaurs.

Let us here clarify that although the ornithischians are also called "bird-hipped," because birds share their characteristic of a backwards-tipped pubic bone, today's birds did not evolve from ornithischians. They evolved from the therapods, the lizard-hipped ones.

The bird-hipped ornithischia included the likes of the stegosaurus, triceratops and iguanodon, which we tend to think of as peaceful giants. These really are extinct. Therapods are not extinct. They turned into parakeets, vultures, ducks and other birds.

"Chilesaurus almost looks like it was stitched together from different animals, which is why it baffled everybody," stated Matthew Baron, a PhD student in Cambridge's Department of Earth Sciences and the joint first author in the paper, which appeared in the journal Biology Letters.

The inverted, bird-like hip structure found in ornithischians enabled their digestive systems to become bigger and more complex, in turn enabling the evolution of gargantuan plant-eaters like Patagotitan mayorum, found in Patagonia in 2014, which as has been pointed out, was probably about 40 meters long and weighed more than the space shuttle.

Chilesaurus, artist's impression
Nobu Tamura, Wikimedia Commons

Chilesaurus wasn't that big, measuring a measly three meters and change from nose to tail-tip. In any case, living on plants isn't very nutritious, hence the need for advanced digestion, to extract the most from the diet.

Like stegosauruses and the other ornithischian pack, Chilesaurus has flattened teeth to grind plant matter. Unlike the ornithischians, it doesn't seem to have had a full beak, just a small non-bony one, Baron told Haaretz.

"There was a split in the dinosaur family tree, and the two branches took different evolutionary directions," said Baron. "This seems to have happened because of change in diet for Chilesaurus. It seems it became more advantageous for some of the meat eating dinosaurs to start eating plants, possibly even out of necessity."

Earlier this year, the same group of researchers argued that bird-hipped dinosaurs and lizard-hipped dinosaurs evolved from a common ancestor. Actually, if both are "dinosaurs," they had to have, the question is who they evolved from. We don't know yet.

Gargoyleosaurus parkpinorum, one of the many, many types of ornithischia, which the odd-looking chilesaurus turns out not to be: it was an early plant-eating theropod.
Firsfron, Wikimedia Commons