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Bizarre 'Frankenstein' chilesaurus is the missing link on dinosaur family tree

17 Août 2017

A weird dinosaur which looked like a raptor but was in fact a vegetarian may be the "missing link" between plant-eating dinosaurs and theropods, the group that includes carnivores such as Tyrannosaurus rex and Velociraptor.

Scientists have solved the puzzle of the so-called "Frankenstein dinosaur", which seems to consist of body parts from unrelated species.

Scientists first described the Chilesaurus in 2015. "It fills the gap quite nicely".

In a study now published in Biology Letters, Baron and colleagues from the Natural History Museum have tried to settle the debate of which group the creature belongs to.

Researchers say their findings will also help them better understand the origins of a group of dinosaurs known as Ornithischia. Likewise, his co-author Barrett said that Chilesaurus should provide new insight into how the dinosaur groups split from one another and ultimately wound up evolving along different paths. Under the newly proposed structure, the Therapoda (two-legged predators like T-rex) and Ornithischia (bird-hipped herbivores like Triceratops and Stegosaurus) groups were closely related, while the Sauropodomorpha (giant long-necked creatures like Brachiosaurus) were more distant cousins. It lived during the Late Jurassic period, about 150 million years ago, and has an odd collection of physical characteristics, which made it hard to classify. After all the studies and finally solving the puzzle, they made a decision to put it along with other dinosaurs completely unrelated to any of their kind: within the ornithischia group, where Triceratops and Stegosaurus are also found. Chilesaurus is one of the very first dinosaurs to be included in this "bird-hipped" group. The dinosaur has a unusual set of physical characteristics that look like they had emerged from different places: its head looks like a carnivore's, for instance, but its teeth are flat and appeared to be made for grinding up plants.

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Chilesaurus has inverted, bird-like hips, but it doesn't have the distinctive, bird-like beak for eating like all the other Ornithischia dinosaurs, such as Stegosaurus or Iguanodon, and that's what makes it so important to paleontologists.

"Chilesaurus is nearly like a velociraptor in terms of its height, length and overall build", Matthew Baron, of the University of Cambridge, said.

"There was a split in the dinosaur family tree, and the two branches took different evolutionary directions", said Baron.

The Chilesaurus present the inverted hips but not the beak-like structure.

"Before this, there were no transitional specimens - we didn't know what order these characteristics evolved in", says Baron. "This seems to have happened because of change in diet for Chilesaurus". "This shows that in bird-hipped dinosaurs, the gut evolved first, and the jaws evolved later". Their suggestion could overturn over a hundred years of theory about the evolution of dinosaurs.

Bizarre 'Frankenstein' chilesaurus is the missing link on dinosaur family tree