The Burgess Shale, one of the world’s most remarkable fossil formations, has yielded yet another extraordinary glimpse into the earliest history of animal life.
The discovery, described as a ‘mother lode’, will further our understanding of the Cambrian Explosion, when early animals diversified across the planet half a billion years ago.
An expedition led by the Royal Ontario Museum discovered more than 50 species, many of them new to science, in just two weeks of digging at the Marble Canyon fossil bed in Canada’s Kootenay National Park.
“There is a high possibility that we’ll eventually find more species here than at the original Yoho National Park site, and potentially more than from anywhere else in the world,” said Dr Jean-Bernard Caron, the curator of invertebrate paleontology at the museum and lead author of the report in Nature Communications.
The new site is 42km from the original Yoho dig, found in 1909 by Smithsonian Institution secretary Charles Doolittle Walcott and popularised in the 1989 book Wonderful Life by Harvard palaeontologist Stephen Jay Gould.
The 505-million-year-old Walcott quarry has produced 200 animal species over the past century.
The Burgess Shale fossils are unusual because they preserved soft body tissues at a time when animals were only just starting to grow hard parts, such as beaks, shells and bones.
The shale was formed after a mudslide buried the creatures living on the sea bed below.
At that time, North America was south of the equator, and lying at a 90 degree angle to its current orientation. Since then, plate tectonics have moved the continent, first pushing into the super-continent Pangea, then splitting it off again. As the Pacific plate crashed into the continent, the fossil bed rose high into the Rocky Mountains.
Many of the Burgess Shale fossils are arthropods, a group which includes trilobites, insects and crustaceans, and which makes up 80 per cent of animal species alive today.
But it also has examples of groups that have long since become extinct.
Walcott mistakenly tried to shoehorn his finds into the classifications of known, living animals and it was only in the 1960s that scientists revisited his samples and realised that many represented evolutionary experiments that had long since become extinct.
Amiskwia Sagittiformis, for example, is a 2.5cm long creature with three body segments, a head with two tentacles, a body with two stubby fins, and a tail. Walcott classified it as an arrow worm and later researchers suggested it might be a ribbon worm but it lacks characteristic features of both. It is currently listed as having no known living or extinct relatives.
Anomalocaris Canadensis, meanwhile, was thought to be three separate creatures when it was first discovered. It’s name means ‘abnormal shrimp’ after its feeding tentacles. The creature, which grows up to 60 cm long, is the largest known predator of the Cambrian era.
The location of the new dig is being kept secret but Parks Canada organises trips to see Walcott’s original quarry, which was designated a World Heritage Site in 1980.