A fossilized fish that scientists estimate is 500 million years old has gill structures that may have evolved into the first jawbone, a new study says.

Named Metaspriggina, the soft-bodied fish has been exceptionally well-preserved and has characteristics that may have later transitioned into the first jawbones in vertebrates with jaws, Live Science reported.

Examples of the species were found among dozens of specimens uncovered about two years ago in Marble Canyon in Canada's Kootenay National Park. The dig unearthed beautifully preserved fossils, some of which were complete down to heart, gut and muscles.

Researchers have placed Metaspriggina in the Cambrian Explosion period dated between 543 million and 493 million years ago. Their findings about the ancient fish have been published in the journal Nature.

"For the first time, we are able to say this is really close to this hypothetical ancestor that was drawn based on a study of modern organisms in the 19th century," said study co-author Jean-Bernard Caron, a paleontologist at the Royal Ontario Museum in Toronto, Canada, as quoted by Live Science.

The fish sporting a purported precursor to the jawbone grew to around 2 inches in length and proliferated North America, The Associated Press reported. It had a flattened head with single-lens eyes on top.

"It allows an understanding of where we come from and what our most distant relatives might have looked like," said Caron, as quoted by Reuters. "Because of its great age--more than half a billion year old--Metaspriggina provides a deep down view at the origins of the vertebrates."

The ancient creature had seven pairs of structures lining the sides of its pharynx, the cavity in the back of the mouth. The first pair matches up with an earlier idea called the serial homology hypothesis from naturalist Karl Gegenbaur, who proposed in the 1870s that a long-lost ancestor fish provided the jawbone link.

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