At least eight new kinds of Earth's earliest animals from the mysterious and controversial Cambrian Explosion have been discovered in a unexpected section of ancient rock 30 miles from the famous Burgess Shale of Canada. The discovery suggests such old, rare fossils are more common than previously thought.
Like the fossils of the original Burgess Shale, the new discoveries are remarkable because they preserve features of animals which had no hard parts — like gills and eyes — and remained intact for more than half a billion years.
That's a time when animals evolved from being very small, simple organisms into a wildly creative, explosive variety of sometimes bizarre creatures.
These were culled by natural selection over time, leaving the more familiar main animal groups we see today.
Among the more dramatic discoveries is a new kind of "anomalocaridid" — the monster shrimp-like top predator a half-billion years ago. Some of these sorts of beasts have been found up to two meters long in shale from Chengjiang, China.
"This one is a new genus and species," said Robert Gaines, one of the co-authors of a report on the discovery published in the September issue of the journal Geology. Detailed descriptions of the other new fossils will be made in additional papers, he said.
"These (different anomalocaridids) are creating the possibility of of linkages between these very rare snapshots," all over the world, said paleontologist Nigel Hughes of the University of California at Riverside. But more compelling is the possibility that there are a lot more such fossils out there preserving the story of one of the most dramatic periods in the history of life.
"What's really exciting is that those (fossils) are so widespread," said Gaines. The key to that, he said, is in the origins of the shale itself.
The first Burgess Shale fossils were from shale that was formed by mud that tumbled off a submarine cliff a half-billion years ago. That was thought to be the reason why the fossils were preserved — because they were in fine mud, buried quickly and deep down where there was no oxygen to help bacteria eat the soft bodies.
These new fossils, however, are from rocks that were once above the cliff edge — on a wide, sloping, muddy seafloor. As a result, it seems more likely that these show the animals in or closer to the habitats in which they lived, explained Hughes.
"It's been controversial to what extent these animals are living in the spot they were found, and to what extent transported there (after death)," Hughes told Discovery News. The fact that the fossils from above the cliff also appear with track marks — unlike the animals that fell over the cliff — strongly suggests that this was where the animals lived, he said.
Although the Burgess Shale was the first place such early soft-bodied animals were discovered, others have since been discovered in the right sorts of rocks in China, Greenland and Australia. None of these appears to have required a cliff-bottom setting either, said Hughes. So the discovery in Canada makes perfect sense.