Chilesaurus: The ‘Missing Link’ Between Plant and Meat Eaters?
A BIZARRE dinosaur which looked like a raptor but was in fact a vegetarian may be the ‘missing link’ between plant eaters and meat eaters such as Tyrannosaurus rex.
Researchers from Cambridge University and the Natural History Museum analyzed more than 450 anatomical characteristics of early dinosaurs and correctly place the creature, known as Chilesaurus, in the dinosaur family tree.
Their findings, published in the journal Biology Letters, suggest that Chilesaurus effectively fills a “large gap” between two of the major dinosaur groups, and shows how the divide between them may have happened.
Chilesaurus, which was discovered in southern Chile, was first described in 2015.
It lived during the Late Jurassic period, about 150 million years ago, and has an odd collection of physical characteristics, which made it difficult to classify.
Its head resembles that of a carnivore, but it has flat teeth for grinding up plant matter.
Study joint first author Matthew Baron, a PhD student in Cambridge’s Department of Earth Sciences, said: “Chilesaurus almost looks like it was stitched together from different animals, which is why it baffled everybody.”
Earlier research suggested that Chilesaurus belonged to the group Theropoda, the ‘lizard-hipped’ group of dinosaurs that includes Tyrannosaurus.
But the new study suggests that it was probably a very early member of a completely different group, called Ornithischia.
The researchers say that the shuffling of the dinosaur family tree has “major implications” for understanding the origins of Ornithischia – the ‘bird-hipped’ group of dinosaurs that includes Stegosaurus, Triceratops and Iguanodon.
The bird-hipped dinosaurs have several common physical traits: the two most notable being an inverted, bird-like hip structure and a beak-like structure for eating.
The inverted hips allowed for bigger, more complex digestive systems, which in turn allowed larger plant-eaters to evolve.
While Chilesaurus has a bird-like hip structure, and has flat teeth for grinding up plants, it doesn’t possess the distinctive ‘beak’ of many other bird-hipped dinosaurs, which is what makes it such an important find.
Mr Baron said: “Before this, there were no transitional specimens – we didn’t know what order these characteristics evolved in.
“This shows that in bird-hipped dinosaurs, the gut evolved first, and the jaws evolved later – it fills the gap quite nicely.”
Co-author Professor Paul Barrett, of the Natural History Museum, said: “Chilesaurus is one of the most puzzling and intriguing dinosaurs ever discovered.
“Its weird mix of features places it in a key position in dinosaur evolution and helps to show how some of the really big splits between the major groups might have come about.”
Mr Baron added: “There was a split in the dinosaur family tree, and the two branches took different evolutionary directions.
“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 dinosaur family groupings need to be rearranged, re-defined and re-named.
In a study published in the journal Nature, the researchers suggested that bird-hipped dinosaurs and lizard-hipped dinosaurs such as T.rex evolved from a common ancestor, potentially overturning more than a century of theory about the evolutionary history of dinosaurs.
The research team believe there are probably “many more surprises” about dinosaur evolution to be found, once characteristics of later dinosaurs are added to their database.