The notorious Tyrannosaurus rex had a ‘bizarre’ vegetarian cousin with a tiny head, long neck and blunt fingers, scientists have revealed and this particular evolutionary puzzle is proving a little tough to solve.
Chilesaurus diegosuarezi discovered in Chile is being referred as a ‘platypus’ dinosaur because of its bizarre combination of characters that resemble different dinosaur groups. Chilesaurus boasted a proportionally small skull, hands with two fingers like Tyrannosaurus rex and feet more akin to primitive long-neck dinosaurs.
“Chilesaurus can be considered a ‘platypus’ dinosaur because different parts of its body resemble those of other dinosaur groups due to mosaic convergent evolution”, says Martín Ezcurra, Researcher, School of Geography, Earth and Environmental Sciences, University of Birmingham. “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. Chilesaurusprovides 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.”
Chilesaurus diegosuarezi is nested within the theropod group of dinosaurs, the dinosaurian group that gathers the famous meat eaters Velociraptor, Carnotaurus and Tyrannosaurus, and from which birds today evolved. The presence of herbivorous theropods was up until now only known in close relatives of birds, but Chilesaurus shows that a meat-free diet was acquired much earlier than thought.
Chilesaurus diegosuarezi is named after the country where it was collected, as well as honouring Diego Suarez, the seven year old boy who discovered the bones. He found the fossil remains of this creature at the Toqui Formation in Aysen, south of Chilean Patagonia, in rocks deposited at the end of the Jurassic Period, approximately 145 million years ago.
Due to Chilesaurus’ unusual combination of characters, it was initially thought that Diego had uncovered several species.
However, since Diego’s find, more than a dozen Chilesaurus specimens have been excavated, including four complete skeletons – a first for the Jurassic Period in Chile – and they demonstrate that this dinosaur certainly combined a variety of unique anatomical traits.
Most of the specimens are the size of a turkey, but some isolated bones reveal that the maximum size of Chilesaurus was around three metres long.
Chilean and Argentinian palaeontologists from institutions including the University of Birmingham, along with Diego’s parents, have been studying these skeletons.
Other features present in very different groups of dinosaurs Chilesaurus adopted were robust forelimbs similar to Jurassic theropods such as Allosaurus, although its hands were provided with two blunt fingers, unlike the sharp claws of fellow theropod Velociraptor.
“Chilesaurus is the first complete dinosaur from the Jurassic Period found in Chile and represents one of the most complete and anatomically correct documented theropod dinosaurs from the southern hemisphere” says Dr. Fernando Novas, Bernardino Rivadavia Natural Sciences Museum, Buenos Aires, Argentina.
Chilesaurus represents one of the most extreme cases of mosaic convergent evolution recorded in the history of life.
For example, the teeth of Chilesaurus are very similar to those of primitive long-neck dinosaurs because they were selected over millions of years as a result of a similar diet between these two lineages of dinosaurs.
The finding was published in the journal Nature.