'Millennium Falcon' fossil shows what it took to thrive 500 million years ago
Cambroraster was similar in some ways to lampreys, stingrays and horseshoe crabs
A new fossil species named after an iconic starship is both unlike anything that exists today and uncannily similar to many modern animals, from stingrays to horseshoe crabs.
When paleontologists first spotted the large, round shield-like fossils in B.C.'s Kootenay National Park, "we really didn't know what to make of it," recalls Joseph Moysiuk, part of the excavation team.
"We nicknamed it 'The spaceship'... because we thought it looked a lot like the Millennium Falcon," he added, referring to Han Solo's iconic ship in the Star Wars series.
It became more than a nickname — the creature's formal scientific name is now Cambroraster falcatus. (The first part of the name refers to the fact that it lived during a time period called the Cambrian and had rake-like claws).
The discovery of Cambroraster will be featured in First Animals, a documentary about the Burgess Shale that will air on CBC-TV's The Nature of Things on Oct. 18.
Moysiuk spotted the first mysterious pieces of Cambroraster fossils in 2014, in a pile of loose rocks at a fossil site called Marble Canyon.
At that time, he had just started his PhD with Jean-Bernard Caron, Richard M. Ivey Curator of Invertebrate Palaeontology at the Royal Ontario Museum and was invited to be part of a field expedition to the site. It contains rich fossil deposits known as the Burgess Shale that date back about 506 million years ago.
Back then, B.C. was near the equator, and Marble Canyon was part of a shallow ocean a few hundred metres deep. The animals that lived there — many unlike anything alive today — were exquisitely preserved after being buried in an underwater landslide.
The first bits and pieces of Cambroraster didn't even look like they could be from the same animal. But in 2016, as the team excavated small quarries into the mountainside, they started finding entire specimens. The "spaceship," it turned out, was a protective carapace or shield covering Cambroraster's head.
Cambroraster was about the size of a painted turtle or a medium pizza — making it huge by Cambrian standards. At that time, most animals were smaller than your little finger, Moysiuk said.
It was an arthropod, a distant relative of crabs, insects and spiders and other animals with jointed legs, although it didn't have any legs itself.
Instead, it swam by flapping a series of "wings" as many stingrays do, researchers think.
The bizarre spaceship-like shield over its head was similar to that of a modern-day horseshoe crab, except that it wasn't a hard shell, but flexible like the exoskeleton of a spider or bee.
Like a horseshoe crab (not a true crab but a distant relative of spiders), Cambroraster dug in the muddy bottom for food such as worms, researchers think, although it did so with a set of rake-like claws studded with hooked spines — something horseshoe crabs definitely do not have, but some relatives of real crabs do.
Cambroraster devoured its prey with a circular, toothy lamprey-like mouth that was the calling card of the extinct group it's part of: the radiodonts (named for their round, toothy mouths), which died out about 350 million years ago.
"Cambroraster is kind showing a mish-mash of traits that we see in some modern groups," said Moysiuk, lead author of a paper describing them, published in the journal Proceedings of the Royal Society B.
"It's telling us that the Cambrian ecosystems were really complex. This is not a sort of primitive, simple organism. This is a highly specialized predator."
Figuring all that out wasn't easy, as many fossils are just pieces, and they're completely flattened. It took more than a hundred fossils squashed from different angles to uncover what the animal looked like in 3D.
Fortunately, Cambroraster fossils were surprisingly common at Marble Canyon, with sometimes dozens of individuals covering a single slab of rock.
Cambroraster is quite different from other radiodont fossils, such as the more agile predator Anomalocaris and other species that swam around further from the sea floor, suggesting that the group was quite diverse, Moysiuk says.
The fact that it has so much in common with modern horseshoe crabs and lived among many creatures with similarities to modern marine organisms tells us something about life 506 million years ago, he added.
"It's not so different from the sort of situation that we have today. We may have different players. But overall, the ecosystems are performing very similarly."