The tiny fish were swimming about the ancient tropical sea 500 million years ago when they were buried alive on the sea floor.
Their squashed remains, uncovered on a windswept mountainside near the B.C.-Alberta border, were held up internationally Wednesday as a “major fossil discovery.”
Scientists say the primitive little fish, called Metaspriggina, gives an unprecedented glimpse of the origin and development of the earliest vertebrates, which eventually led the way to evolution of dinosaurs and mammals, such as humans.
“It is basically allowing us to peer into our deepest roots,” says Jean-Bernard Caron, a paleontologist with the Royal Ontario Museum, who led the team that found the exquisitely preserved specimens in a “motherlode” of fossils uncovered at a secret location in Kootenay National Park.
Plenty more ancient treasure is expected to turn up during a 10-week international expedition back to the fossil bed this summer.
“I am so thankful that the site was found in a national park, “ says Caron, referring to the way Parks Canada is controlling access to the site to prevent pillaging.
Metaspriggina lived 505 million years ago when life was exploding in new directions. It swam in a world then dominated by small, strange looking creatures, many of which resemble today’s shrimps and crabs, says Caron.
Metaspriggina was tiny. “They are no longer than my thumb,” he says of the fossils.
But some are so well preserved their muscles and nasal structures are visible.
“Even the eyes are beautifully preserved and clearly evident,” says Simon Conway Morris at the University of Cambridge, co-author of a report on Metaspriggina published Wednesday in the journal Nature.
The scientists say the fish had “unambiguous vertebrate features” and striking “branchial arches” on either side of its body.
The arches likely helped the primitive fish eat and breathe, and appears to be the one of the first steps toward to the evolution of jaws. “It’s the first stage of a series of transformations that led to the jaws,” says Caron.
The “stunning” fossils, as Conway Morris describes them, enabled the scientists to classify Metaspriggina as one of the first primitive fishes that they say was common in the ancient seas.
The Kootenay fossil bed, which Caron and his colleagues discovered in 2012, is about 40 kilometres from the more famed Burgess Shale sites, discovered more than a century ago and long considered among the richest fossil beds in the world. They all formed during the Cambrian explosion when many forms and new branches of life emerged. Some died out while others evolved into animals seen today.
Caron says there are striking differences between the locations, with the older Burgess shale sites dominated by arthropods, with only two partial fossils of Metaspriggina among the 200,000 samples collected over the years.
The Kootenay site is not necessarily better or richer but “complements” the other sites, he says, noting it had already yielded more than 40 fish specimens.
“I’m going to start calling this site the fossil fish bed,” Caron says, who will head the 10-week expedition this summer with researchers from Canada, the U.S. and Europe. The location of the fossil bed is not being released with Parks Canada and the scientists saying only that it is located near Marble Canyon.
Caron’s team first stumbled upon the site in 2012 when they came across fossils littering a mountainside. Over a two-week period they pulled out many high-quality specimens including the Metaspriggina fossils.
Caron says the creatures lived in a “dynamic” environment in an ancient tropical sea near the equator.
“These animals would have been trapped in very quickly in mudflows that would have buried them alive,” he says. Mudflows repeatedly trapped creatures in layers for thousands of years and built up layers on the sea floor.
Over the eons the sea floor — along with its fossils — was pushed up onto the Rocky Mountains.
Some fossil beds have eroded away while others ended up on inaccessible cliffs, but Caron says the Marble Canyon fossil bed is horizontal.
“This one is great for us as there are no cliffs above, so no potential rockfalls, the rock layers are pretty much flat, the way they were deposited 500 million years ago,” he says.
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