Unique Dinosaur May Be Missing Link Between Carnivores & Herbivores

The skeleton of a Chilesaurus diegosarezi. (Credit: Machairo/Wikipedia)

(CN) – A raptor-like dinosaur with an unusual set of physical characteristics may be the “missing link” between plant-eating species and theropods – the group that includes carnivores like the Tyrannosaurus rex.

Known as Chilesaurus, the dinosaur’s unique features have confused scientists since it was discovered in southern Chile in 2004. Chilesaurus was first described in 2015.

Using a comprehensive dataset to analyze more than 450 anatomical characteristics, researchers from the University of Cambridge and the Natural History Museum were able to finally place Chilesaurus in the dinosaur family tree, they report Tuesday in the journal Biology Letters.

The findings suggest that Chilesaurus fills a significant gap between two of the primary dinosaur groups, and reveal how the divide between them may have occurred.

Chilesaurus almost looks like it was stitched together from different animals, which is why it baffled everybody,” said co-lead author Matthew Baron, a doctoral student at Cambridge.

The odd-looking dinosaur lived during the Late Jurassic period, about 150 million years ago, and features a carnivore-like head but flat teeth for grinding up plant material.

While previous research suggested that Chilesaurus was a part of the group Theropoda – which includes “lizard-hipped” dinosaurs like Tyrannosaurus – the new findings show that it was an early member of a separate group called Ornithischia. Such a reclassification has major implications for establishing the origins of Ornithischia, the “bird-hipped” group of dinosaurs that includes Stegosaurus and Triceratops.

Reconstruction of the Chilesaurus diegosarezi. (Credit: Nobu Tamura/Wikipedia)

“Chilesaurus is one of the most puzzling and intriguing dinosaurs ever discovered,” said co-author Paul Barrett, a professor at the Natural History Museum. “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.”

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 allow for larger, more complex digestive systems which enabled larger plant-eaters to evolve.

Though Chilesaurus features flat teeth for eating plants and a bird-like hip composition, it does not have the beak-like structure typical of many other bird-hipped dinosaurs – a distinction that makes it a particularly important find.

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

“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 team argued that dinosaur family groupings have to be rearranged, renamed and redefined. In a report published in the journal Nature, the researchers suggested that lizard-hipped and bird-hipped dinosaurs evolved from a common ancestor. This finding could overturn recent theory on the evolutionary history of dinosaurs.

The team’s dataset currently analyzes only early dinosaurs, and there are likely several more surprises about dinosaur evolution to be found among later species, according to the study.


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