Meet this 500 million-year-old, taco-shaped marine creature that has 30 pairs of legs

Scientists from the Royal Ontario Museum (ROM) have finally uncovered secrets of a marine creature that lived roughly 505 million years ago.

Called Odaraia alata, this strange-looking critter lived in Earth's earliest oceans at a time when there was a burst of life on the planet, often referred to as the Cambrian explosion. 

Odaraia had been discovered more than 100 years ago in British Columbia's Burgess Shale — an area that contains a treasure trove of fossils even to this day — but not a lot was known about it.

Even almost 70 years after its discovery, a 1981 study left in question such things as whether or not it had mandibles (jaw bone-like structures), how it fed and exactly how many legs it had, leaving paleontologists wondering just where it belonged in animal classification.

A new study published in the journal Proceedings B revealed that this 20-centimetre-long arthropod was not only a great swimmer with its 30 pairs of sea legs — which the authors discovered were quite complicated structures — but it did indeed have mandibles.

This puts Odaraia into a group called mandibulates, which are related to some animals and insects we see today, including crabs, centipedes, ants and mosquitoes. And it is one of the earliest of its kind.

It is these arthropods that make up more than 80 per cent of the animals we have today.

"We had a really good reconstruction of this animal in the 1980s, by Prof. Derek Briggs, who is now at Yale University," said the paper's lead author, Alejandro Izquierdo López, who was based at the ROM during this work as a PhD student at the University of Toronto.

"It's not until now that we have the material evidence for these ideas. Now we know exactly what it was feeding on and how it was feeding."

The ROM contains the largest collection of Cambrian fossils found in the Burgess Shale.

"Thanks to the work we have been doing at the ROM on amazing fossil animals ... we already know a substantial amount about the early evolution of mandibulates," study co-author Jean-Bernard Caron, the Richard M. Ivey Curator of Invertebrate Paleontology at the ROM, said in a release. "However, some other species had remained quite enigmatic, like Odaraia."

It turns out that Briggs had a lot right with this funky marine animal.

Not only did it only have mandibles, but it's believed that Odaraia swam upside down to catch a meal. But how did it catch a meal with its taco-shaped carapace that covered its 30 sets of legs?

It turns out those legs are incredibly intricate.