Missing link found between herbivorous and carnivorous dinosaurs

Researchers have determined that the dinosaur known as Chilesaurus could be the “missing link” that shows how the major divide happened between herbivorous and carnivorous dinosaurs. The unusual creature looked like a meat-eating raptor, but was actually a plant-eating dinosaur.

While most dinosaurs were herbivores, theropods such as Tyrannosaurus were lizard-hipped carnivores. Researchers initially had a difficult time classifying Chilesaurus, a dinosaur first discovered in southern Chile. He had a collection of characteristics that made him resemble both plant-eaters and meat-eaters.

“Chilesaurus almost looks like it was stitched together from different animals, which is why it baffled everybody,” said first author Matthew Baron.

Scientists from the University of Cambridge and the Natural History Museum used a comprehensive dataset to analyze over 450 anatomical features of dinosaurs in order to fit Chilesaurus into the dinosaur family tree.

First identified in 2015, the Chilesaurus lived about 150 million years ago during the Late Jurassic Period. Its head looked like that of carnivorous dinosaurs, but it had the flat teeth of plant-eaters.

Earlier research placed Chilesaurus into the group Theropoda, but the new study suggests that it was an early member of a completely different group known as Ornithischia. This may help researchers understand the origins of Ornithischia, which includes Stegosaurus, Triceratops and Iguanodon.

This group of dinosaurs had several physical characteristics in common. Most distinctively, they had an inverted, bird-like hip structure and a type of beak for eating. Chilesaurus had the bird-like hips and flat teeth for eating plants, yet it did not have the beak structure. This was a very significant discovery.

“Before this, there were no transitional specimens – we didn’t know what order these characteristics evolved in,” said Baron. “This shows that in bird-hipped dinosaurs, the gut evolved first, and the jaws evolved later – it fills the gap quite nicely.”

The researchers say that there is still a lot to learn about the family tree of dinosaurs.

“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.”

The study, published in Nature, suggests that bird-hipped dinosaurs and lizard-hipped dinosaurs such as Tyrannosaurus evolved from a common ancestor. This would disrupt over a century of theory about the evolutionary history of dinosaurs.

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By Chrissy Sexton, Earth.com Staff Writer