Jaws Evolved With The Reorganisation Of The Brain And Sensory Organs

Reorganisation of the brain and sensory organs could be the key to vertebrate success according to a paper published by an international team of researchers. The study claims to have solved a scientific riddle by studying the skulls of primitive, jawless fish known as the galeaspids. Instead of breaking up the fossils and physically looking at the remains under a microscope, the team used a machine known as a synchotron. The synchotron in question is the largest in the world.

A computer model of the sychotron at Switzerland.
The offshoots are the individual  'microscope' moduals

Based in Switzerland, it is a vast particle accelerator that fires high energy electrons round a circuit. When they approach the speed of light, they have enough energy to penetrate solid rock. The machine can be used to x-ray fossils without damaging them in any way and build up a three dimensional, manipulable model. Palaeontologists and physicists from the University of Bristol (UK), the Institute of Vertebrate Palaeontology and Palaeoanthropology (China), the Museum National D'Histoire (France) and the Paul Scherrer Institut (Switzerland) have collaborated to study the galeaspid fossils and vertebrate evolution.

An artist's rendition of a galeaspid and the
structure of its brain and sensory organs

The team leader, Gai Zhi-Kun, said 'we were able to see the paths of all the veins, nerves and arteries that plumbed the brain of these amazing fossils. They had brains much like living sharks, but no jaws.' The origin of teeth and jaws is believed to be one of the biggest steps in evolution. The fossils date from the time just before the evolution of those body parts. This has led the team to believe that the structure of the brain and sensory organs were rearranged just before jaws and teeth evolved in vertebrates.

In the embryology of living vertebrates, jaws develop from stem cells that migrate from the hindbrain and down between the developing nostrils. This cannot happen in living jawless vertebrates as there is a single nasal organ that gets in the way. All vertebrates were originally jawless and therefore they could not have evolved jaws unless the structure of the brain and sensory organs changed. Professor Min Zhu stated that 'this is the first real evidence for the steps that led to the evolutionary origin of jawed vertebrates and the fossil provides this with rock solid proof.'