Left: This is an illustration of Metaspriggina swimming. Drawing by: Marianne Collins. © Conway Morris and Caron. Right: This is a fossil of Metaspriggina from Marble Canyon -- head to the left with two eyes, and branchial arches at the top. Photo by: Jean-Bernard Caron © ROM. (Photo : Left: Drawing by: Marianne Collins. © Conway Morris and Caron. Right: Photo by: Jean-Bernard Caron © ROM./ Eurekalert )

The 505-million-year-old fossil of a creature called Metaspriggina shows how vertebrates developed jaws, according to a new study by University of Cambridge researchers.

According to the researchers, the fossil of the tiny fish has well-preserved arches near the front of its body. These arches later gave rise to the jaws in vertebrates, including humans. This is the first time that the structures have been found so early in fossil history.

The fossils in the study came from several locations including the Burgess Shale site in Canada's Rocky Mountains. Researchers say that the site has some of the most well-preserved fossils from the Cambrian Period.

Metaspriggina study could also help scientists understand a critical time in Earth's history - the Cambrian explosion. This period saw rapid evolution of animals around 540 million years ago.

Previous research on the fish was based on incomplete specimen. The latest fossils helped researchers understand the shape and position of rod-like structures known as the gill or branchial arches.

Scientists also found that these fishes were active swimmers and that they had a pair of large eyes and nasal structures that helped them sense their environment. Metaspriggina was soft bodied and was not bigger than a human thumb.

"The detail in this Metaspriggina fossil is stunning," said lead author Professor Simon Conway Morris of Cambridge's Department of Earth Sciences, according to a news release. "Even the eyes are beautifully preserved and clearly evident."

The earliest evidence of jaw-like structure makes the new fossil of Metaspriggina an incredible finding, researchers said. Previously, scientists had assumed that the branchial arches existed as singles. But, the newly-found specimen shows that the arches were in pairs.

"Obviously jawed fish came later, but this is like a starting post - everything is there and ready to go," said Dr Jean-Bernard Caron of the University of Toronto, who is also the co-author of the study. "Not only is this a major new discovery, one that will play a key role in understanding our own origins, but Marble Canyon, the new Burgess Shale locality 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."

The study is published in the journal Nature.