Life before jaws: Meet your ancestor

Scientists have identified the first clearly preserved fossils of an ancient, minnow-sized fish that had curved pieces of cartilage that opened a mouth-like cavity. Nature/The Canadian Press

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Your ancient ancestors are now revealed from a time 505 million years ago when primitive animals had only the faint beginnings of jaws.

In an era more than twice as far back as the first dinosaur, minnow-sized fish had curved pieces of cartilage that opened a mouth-like cavity.

Today’s vertebrate animals (those with spines) all evolved from these fish, scientists say. And now they have identified a major find: the first clearly preserved fossils of one such ancient fish — in British Columbia’s mountains.

Add wiggly little Metaspriggina to the human family tree.

What was this fish?

It swam in an ocean where the Rocky Mountains now stand. It was about six centimetres long and swam along filtering little organic bits from the water, as some whales do today. When it died it became a fossil in the Burgess Shale, a trove of so much ancient life.

What’s so special about it?

It had no jaws, but we can see where they came from. Rows of curved pieces of cartilage that look a little like a rib cage supported its mouth and throat cavity. The front two pairs of these “bronchial arches” evolved in time into jaws and the bones of the throat.

And fish like these are our ancestors?

“Yes,” answered Jean-Bernard Caron, a curator at the Royal Ontario Museum. “This tells us a lot about what we looked like at the time of the Cambrian.”

The museum and Cambridge University found the fish fossilized and published a study in the journal Nature.

The discovery “connects to our deepest roots and allows us to answer the question: Where do we come from?” he said.

Land animals and even modern fish weren’t around yet. “This is very primitive,” said Caron.

Is this the oldest known fish?

“It’s not the first fish found. The oldest ones are from China, a few million years older. But it’s the clearest in terms of the preservation of key features which eventually evolve into the jaws.”

In this photo of fossilized metasprigina from Marble Canyon in Kootenary National Park, the head is on to the left.

In this photo of fossilized metasprigina from Marble Canyon in Kootenay National Park, the head is on to the left. Jean-Bernard Caron / Royal Ontario Museum

We’ve known ancient fossils for centuries. Why is this only emerging now?

Its fossil came to light in 2012 in the Burgess Shale formation that preserves many species more than 500 million years old.

The fish was soft-bodied. Dinosaur bones fossilize well but soft tissue doesn’t. But the Burgess Shale formed from mud that buried animals in a deep sea environment without oxygen where soft tissues didn’t decay.

Though people had theorized that fish with arches instead of jaws might exist, “it had eluded scientists,” Caron said. “Here we have for the first time fossil evidence for that theory.”

Where is it?

Marble Canyon, in Kootenay National Park.

Caron: “Being in a national park allows this site to be protected for all generations, which is a huge thing.”

The team will return to the same formation this summer. “There’s probably way more to find at that site and the neighbouring mountains.”

What happened to the rest of the branchial arches over time?

Modern fish still have them. They support the gills.










