A team of French and Swedish researchers solved the mystery behind the formation of face in vertebrates including humans. The researchers studied the evolution of an ancient fish, Romundina to explain how jawless vertebrates transformed to creatures with jaws. They said that the evolution of jaw led to the development of the face.
There are two types of vertebrates (backboned animals) - jawless and jawed. Only lampreys and hagfishes belong to jawless vertebrates, while more than fifty thousand species, including humans constitute jawed vertebrates. It is a known fact that jawed vertebrates evolved from jawless ones, where an anatomical transformation turned the face inside out.
Researchers concentrated on the small primitive armoured fish, Romundina, because it was one of the earliest jawed fishes that displayed features observed in both jawless fishes and modern ones. The researchers studied the fossilized the remains of Romundina that were discovered in the Canadian Arctic. The fish head had a distinct anatomy - short forebrain and an odd 'upper lip' protruding forward in front of the nose, Reuters reports.
Using high-energy X-ray imaging, the scientists studied the skull of Romundina and created a step-by-step evolution of the face.
Researchers said that lumps of tissue grow forward on either side of the brain in the embryos of jawless vertebrates. The tissue converges at the center to develop into a big upper lip enclosed by a single midline 'nostril' right in front of the eyes. The same tissue in jawed vertebrates cultivates forward in the midline under the brain, pushing the chunks between the left and right nasal sacs that opens separately to the outside.
This is the reason why human's face has two nostrils instead of a single big hole in the middle.
The researchers also found that the front part of the jawed vertebrate's brain is longer, which is why the nose is located at the front of the face rather than far back between the eyes.
In Romundina, the researchers discovered separate left and right nostrils. But they are positioned far back, behind an upper lip similar to that of a jawless vertebrate.
"This skull is a mix of primitive and modern features, making it an invaluable intermediate fossil between jawless and jawed vertebrates", Vincent Dupret of Uppsala University, one of two lead authors of the study, said in a press release.
"In effect, Romundina has the construction of a jawed vertebrate but the proportions of a jawless one", says Per Ahlberg, of Uppsala University and the other lead author of the study. "This shows us that the organization of the major tissue blocks was the first thing to change, and that the shape of the head caught up afterwards."
The finding is published in the journal Nature.
