Ancient Fish 'Romundina' Solves Mystery of Facial Evolution in Vertebrates

In order to solve the mystery of facial evolution in vertebrates including humans, experts turned to study the evolution on an ancient fish, Romundina.

Documented in the journal Nature, a team of French and Swedish researchers studied an ancient fossilized fish called Romundina to explain how humans and other vertebrates developed the most significant part of the anatomy- the face.

The researchers studied the skull of the fish using high-energy X-ray imaging and constructed a step-by-step evolution of the face.

Previously, vertebrates were jawless. However, only a few jawless vertebrates exist today like lampreys, hagfishes. It is clear that jawed vertebrates evolved from the jawless ones.

Researchers focused on the small primitive fish Romundina because it was one of the earliest jawed fishes that had a mix of features seen in jawless fishes and modern ones. The fish, the fossilized remains of which were uncovered in Canadian Arctic, had an extremely distinctive anatomy, reports Reuters.

According to the current study, within the embryo of jawless vertebrates, chunks of tissues cultivated forward on both sides of the brain and intersected at the center to form a big upper lip surrounded by a single midline 'nostril' right before the eyes.

However, in jawed vertebrates the same tissue grows forward in the midline under the brain, pushing the tissue between the left and right nasal sac that opens separately to the exterior. 

This is the reason why human face has two nostrils and not just a single gap in the center. Apart from this, the front part of the brain is also longer in jawed vertebrates due to which the nose is placed in the front of the face and not at the far back between the eyes.

The ancient fish Romundina has separate left and right nostrils that are placed at the back behind the upper lip that is similar to the jawless vertebrates.

"This skull is a mix of primitive and modern features, making it an invaluable intermediate fossil between jawless and jawed vertebrates", says Vincent Dupret of Uppsala University, one of two lead authors of the study.

The skull of the ancient fish was imaged at European Synchrotron Radiation Facility using X-rays. 

"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 fossilized skull used in this study is a part of a collection of the French National Natural History Museum in Paris.