Meet T. rex’s vegetarian cousin: Chilesaurus

Chuck Bednar for – @BednarChuck

Therapods, a group of dinosaurs that include the likes of Tyrannosaurs and Velociraptors, are typically viewed as ferocious predators, but a team of researchers has reportedly discovered the vegetarian cousin of these vicious meat-eaters at a site in southern Chile.

Fernando Novas of the Argentinian Museum of Natural Sciences and his colleagues reported the discovery in Monday’s edition of the journal Nature, explaining that the bizarre, enigmatic lizard lived during the Late Jurassic period and telling National Geographic that it looked like a strange mash-up of therapods, saurpods, ornithischians, and basal crocodyliforms.

The creature was named Chilesaurus diegosuarezi in honor of the son of the geologist who first discovered the bones, and Novas told Nat Geo that his team initially believed it was just a typical Jurassic-era dinosaur. They soon discovered that the specimen was anything but typical.

An odd mash-up of different dinosaur parts

It’s pelvic bones resembled those of a stegosaurs or triceratops, while its vertebrae had therapod-like perforations and its teeth, neck and limbs were similar to a brontosaurus. The unusual set of features led them to compare it to the three other groups to see which it was most like, and they found it was a therapod that evolved from a meat-eater to a plant-eater.

While shifts from carnivore to herbivore are relatively rare during the course of evolution, they are not unprecedented – for instance, pandas evolved from the same meat-eating ancestor as the polar bear and the grizzly bear.

“We realized that these specimens belonged to a new species and entirely new group of dinosaurs when we finished to remove the surrounding rock from the first articulated skeleton,” Martin D. Ezcurra, a doctoral researcher at the University of Birmingham School of Geography, Earth and Environmental Sciences and co-author of the study, told redOrbit via email.

“At that point, it was around early 2012, we realized that this dinosaur was not similar to anything known before,” he added. “We felt very excited about this discovery, but at the same time puzzled because it will represent a very hard work to figure out the position of this animal in the ‘dinosaur genealogical tree’ and its implications for the evolution of the entire group.”

First herbivorous theropod from the Southern Hemisphere

This is not the first plant-eating therapod to be discovered, Nat Geo said, but it is the first to come from this early in the evolutionary record and were far less common that Chilesaurus. Novas told Nat Geo that the discovery was “just the tip of the iceberg” and that he expected to find more specimens, both of Chilesaurus and of the predators that hunted it.

Ezcurra told redOrbit that their newly-discovered creature “belongs to a completely unknown lineage of dinosaurs that acquired herbivore habits from carnivorous ancestors and was probably endemic from South America. Also, Chilesaurus is the first herbivorous theropod (a lineage that includes predominantly carnivorous forms) from the Southern Hemisphere.”

“The most interesting about Chilesaurus is the story that it tells about how evolution works,” he added. “We can see in Chilesaurus how evolutionary pressures acted in its ancestor species and produced a very similar anatomical regions to those independently reached by other different groups of unrelated dinosaurs. Chilesaurus shows how evolution works in deep time.”


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