It sounds a bit like a Disney movie: a tyrannosaurus rex that decides it's done with all the blood and bone crunching and decides to switch to a full-on vegetarian diet.
That might not be exactly what happened with the Chilesaurus diegosuarezi dinosaur, but there's no doubt the beast is a bit of an outlier. Researchers describing the dinosaur in the journal Nature this week say that it is indeed a close relative to T. rex and other meat eaters in the theropod group of dinosaurs that also includes velociraptor and carnotaurs -- even though it only ate plants.
And that's not the only thing that's a bit odd about Chilesaurus. The researchers say that even though it has arms like its theropod cousins, those arms were crowned with two blunt fingers rather than sharp claws like those possessed by the velociraptor. It also has blunt teeth and feet similar to long-necked dinosaurs and a smaller skull than other theropods.
This combination of traits, for which Chilesaurus is being referred to as a "playtpus" dinosaur, comes about through a phenomenon known as convergent evolution in which a creature's physical characteristics are shaped by its lifestyle.
"Chilesaurus can be considered a 'platypus' dinosaur because different parts of its body resemble those of other dinosaur groups due to mosaic convergent evolution," said University of Birmingham researcher Martín Ezcurra. "In this process, a region or regions of an organism resemble others of unrelated species because of a similar mode of life and evolutionary pressures. Chilesaurus provides a good example of how evolution works in deep time and it is one of the most interesting cases of convergent evolution documented in the history of life."
The first fossils of Chilesaurus diegosuarezi were found by a seven-year-old boy named Diego Suárez who was south of Chilean Patagonia with his geologist parents studying the formation of the Andes. It was first thought that Diego had found the bones from several different species of dinos thanks to Chilesaurus' strange makeup. But four complete skeletons -- in addition to evidence from 12 specimens -- have since been unearthed there. For his discovery, the young budding paleontologist was rewarded by having the new dino named after him.
Examination of the fossils has led researchers to believe that Chilesaurus was about the size of a turkey, but that it could reach lengths up to 10 feet (3 meters).
"Chilesaurus shows how much data is still completely unknown about the early diversification of major dinosaur groups," Ezcurra said. "This study will force palaeontologists to take more care in the future in the identification of fragmentary or isolated dinosaur bones. It comes as false relationship evidence may arise because of cases of convergent evolution, such as that present in Chilesaurus."