New dinosaur poses evolutionary puzzle

Species discovered in Chile is closely related to Tyrannosaurus rex but was vegetarian

Chilesaurus diegosuarezi, a vegetarian dinosaur despite being a close relative of famous meat-eaters like Tyrannosaurus rex. Photograph: Gabriel Lio

Chilesaurus diegosuarezi, a vegetarian dinosaur despite being a close relative of famous meat-eaters like Tyrannosaurus rex. Photograph: Gabriel Lio

 

A new kind of dinosaur, discovered in Chile by a young boy, has proven to be an evolutionary puzzle. It is closely related to famous meat-eater dinosaurs, including Tyrannosaurus rex, but was itself a vegetarian.

It also mixes a bizarre range of characteristics from unrelated dinosaur species, leading palaeontologists to describe it as a platypus dinosaur.

Most families have one, the odd one out who doesn’t seem to look like the rest of the group. The Chilesaurus diegosuarezi takes this to the extreme, and not just in its preference for leaves and plants over a Stegosaurus steak or a Brontoburger.

Most of the dozen Chilesaurus specimens excavated so far are about the size of a modern-day turkey, but larger bones suggest the big ones could have been three-metres long.

It is related to tough guys such as the Velociraptor and Carnotaurus, but has a proportionally smaller head and feet that are more like those of the long-neck dinosaurs, according to the authors of a study of the species published in Nature.

It also had plant-chomping teeth like those of primitive long-necked dinosaurs, rather than the pointy gnashers of its theropod relatives.

Previously unknown

Experts are excited, not just because it was a previously unknown species that dates back to 145 million years ago.

Its admixture of unique anatomical traits makes it one of the most extreme cases of what is known as “mosaic convergent evolution” recorded in the history of life.

This happens when one organism has characteristics from other unrelated species due to a similar mode of life, explains Dr Martin Ezcurra of the University of Birmingham.

In effect, it borrows useful traits from other species because they suit the animal’s particular lifestyle.

Its discovery is a story in itself. Diego Suarez (7) found the fossilised bones while searching for decorative stones with his sister Macarena. They were with their geologist parents who were studying rocks in Chilean Patagonia.

The species must have been very successful despite its oddities, given it came to be “by far the most abundant dinosaur in southwest Patagonia”, lead researcher Dr Fernando Novas, of Bernardino Rivadavia Natural Sciences Museum in Argentina, said.