505-Million-Year Old Fossilized Fish Offers Clues about the Origin of Jaws in Vertebrates

A well preserved fossilized prehistoric fish has been discovered that offers clue to how vertebrates developed jaws, a new study reveals.

Researchers at the University of Cambridge have discovered a fossilized fish specimen, which is 505-million-years old, and belongs to the Cambrian period. The tiny fish, dubbed Metaspriggina, carries pairs of well preserved arches near the front of the body. These arches later led to the development of jaws in both vertebrates and humans, it is believed. 

The fossil was retrieved from the Burgess Shale site in Rocky Mountains, Canada, a site rich in Cambrain fossil deposits.

Apart from offering clues on the evolution of jaws in vertebrates, fossils from this site including Metaspringgina, shed light on the Cambrian 'explosion'. This period witnessed the dramatic evolution of animals some 540 million years ago.

Prior to this, researchers had identified two incomplete specimens of Metaspriggina. Later, during an expedition in 2012, 44 new Burgess Shale fossils were retrieved. Using these fossils along with other specimens the researchers reclassified Metaspriggina as one of the first vertebrates.

The fossils that date from 505 million years ago reveal clearly how rod like structures called grill or branchial arches developed in prehistoric vertebrates.

On analyzing the arrangement of the muscles the researchers claim that the fish were active swimmers. The animals used their large pair of eyes to view the world and used the nasal structures to sense their surroundings.

"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."

Prior to this, it was assumed that branchial arches existed in series of singles. But the new fossil reveals that the arches occur in pairs.

"Once the jaws have developed, the whole world opens," said Professor Conway Morris. "Having a hypothetical model swim into the fossil record like this is incredibly gratifying."

The finding was documented in the journal Nature.