When you examine your face in the mirror, do you ever wonder how the most unique and identifying part of your body originated and developed?
Writing in a new study published in Nature, a team of French and Swedish researchers offers new fossil evidence that just might explain why we have protruding noses with two nostrils, rather than one big hole between our eyes.
Using special high-powered X-ray imaging equipment, researchers studied a series of fish fossils that ranged in age from ancient to a bit more recent. In the middle of that series of fossils was the skull of a 410-million-year-old, long-extinct species called Romundina a member of the Placoderm (armored fish) class of fish from the Devonian period – 419.2 to 358.9 million years ago.
Scientists know vertebrates evolved from jawless species into those with jaws. Researchers describe this structural transformation as dramatic, causing the face to effectively turn inside out.
Most of today’s vertebrates have jaws; the only species that don’t are lamprey (eels) and hagfishes.
By placing the Romundina in the middle of their fossil sequence, between more primitive and advanced species, researchers were able to map out the main steps of the transition between jawless and jawed vertebrates.
They noted that as the embryos of jawless vertebrates developed, blocks of tissue grew forward on each side of the brain, where they met in the mid-front of the face and formed a big upper lip that surrounded one centrally located nostril just in front of the eyes.
For jawed vertebrates, they found that this same tissue grew forward just under the brain but then pushed its way between the fish’s left and right nasal sacs, which opened to the outside independently of each other.
The researchers say that this particular evolutionary change is why our faces have two nostrils instead of one big hole in the middle like the jawless vertebrates. And, the reason why our nose is located at the front of our face is because the brain of jawed vertebrates also happens to be much longer than the jawless; otherwise our nose would be positioned much further back between our eyes.
Up until they released their findings, the French and Swedish research team said that very little was known about the intermediate steps of the transformation between jawless and jawed vertebrates.