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This Cambrian Bottom Feeder Kickstarted the Evolution of Jaws

Metaspriggina is persona grata in the Phylum Chordata.
YouTube/The Cosmos News video about Metaspriggina narrated by a robot.

In what's being hailed as a major new discovery, paleontologists based out of the Royal Ontario Museum and Cambridge University have identified a key player in early vertebrate evolution. The bottom-feeder Metaspriggina, which swam the Cambrian seas about 505 million years ago, is the earliest known animal to develop anything resembling jaws. The team excavated the fossils in British Columbia's Marble Canyon in 2012, and published their research yesterday in Nature.

Jean-Bernard Caron, the study's co-author, put the finding into perspective in the team's statement. “Not only is this a major new discovery, one that will play a key role in understanding our own origins, but Marble Canyon […] itself has fantastic potential for revealing key insights into the early evolution of many other animal groups during this crucial time in the history of life," he said.

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Marble Canyon is part of Canada's fossil-rich Burgess Shale formation, which is famous for producing well-preserved organisms from the Cambrian. The Metaspriggina fossil bed was no exception. Paleontologists were able to collect 40 specimens of the animal, where before there had only been two (and they weren't in great condition).

Fortunately, the new glut of fossils survived their half-billion years of beauty sleep very well. Researchers could pick out the animal's liver, gills, eyes, muscular arrangement, and prototype jaws from their remains.

“The detail in this Metaspriggina fossil is stunning,” said the study's lead author Simon Conway Morris. “Even the eyes are beautifully preserved and clearly evident.”

Metaspriggina. Image: Marianne Collins, © Conway Morris and Caron

Eyes are great and all, but the animal's branchial arches are the real prize. Paleontologists had previously assumed that these cartilage support beams in the animal's mouth only curved in one direction.

But the new fossils obviously show a series of paired arches, indicating the very beginnings of an upper and lower jaw. While most of the arches evolved to buttress the animal's gills, the ones at the very front of the head were conspicuously thicker than the others, making Metaspriggina the first animal that we know of to set aside valuable mouth-space for some fledgling jaws.

“Once the jaws have developed, the whole world opens,” noted Morris. “Having a hypothetical model swim into the fossil record like this is incredibly gratifying.”

The Metaspriggina fossils display a number of other obvious vertebrate adaptations. The animal had a thin notochord, for example, which would have provided it with axial support. Its single-lens eyes enabled it to gaze in front and above itself, and it was equipped with a pair of nasal sacs and an inkling of a skull.

Perhaps my favorite feature from the study, however, is the animal's “post-anal tail.” All chordates have one, but it still sounds like some kind of futuristic genetic hack.

Post-anal tails aside, the new abundance of Metaspriggina fossils has shed significant light on Cambrian vertebrate evolution, especially when it comes to our jaws. It's also given us a chance to get better acquainted with one of our oldest evolutionary granddaddies. And given that Caron and his colleagues are planning another expedition to Marble Canyon this summer, this is probably not the last we'll hear from the Cambrian fish that taught us all how to chomp.