How vertebrates developed faces millions of years ago

A team of French and Swedish researchers have presented new fossil evidence for the origin of our face.

Using micron resolution X-ray imaging, they showed how a series of fossils, with a 410 million year old armoured fish called Romundina at its centre, documents the step-by-step assembly of the face during the evolutionary transition from jawless to jawed vertebrates.

Vertebrates, or backboned animals, come in two basic models: jawless and jawed.

Today, the only jawless vertebrates are lampreys and hagfishes, whereas jawed vertebrates number more than fifty thousand species, including ourselves.

It is known that jawed vertebrates evolved from jawless ones, a dramatic anatomical transformation that effectively turned the face inside out.

The scientists studied the skull of Romundina, an early armoured fish with jaws, or placoderm, from arctic Canada. The skull is part of a collection of the French National Natural History Museum in Paris.

By imaging the internal structure of the skull using high-energy X-rays at the European Synchrotron (ESRF) in Grenoble, France, the authors show that the skull housed a brain with a short front end, very similar to that of a jawless vertebrate.

"In effect, Romundina has the construction of a jawed vertebrate but the proportions of a jawless one", Per Ahlberg, of Uppsala University and one of the other lead authors, said.

"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", he added.

By placing Romundina in a sequence of other fossil fishes, some more primitive and some more advanced, the authors were able to map out all the main steps of the transition.

The research is published in the journal Nature.