Early Vertebrates and the Emergence of Jaws

The evolution of jaws marked an important transition in the evolution of vertebrates, allowing them to become successful, active predators. Some developmental events associated with this transition can be deduced from the fossil record of jawless vertebrates, with new discoveries suggesting that the separation of the nasal sacs in jawless vertebrates was a key step in the evolution of jaws. Some members of the earliest jawed vertebrates, the placoderms, have recently been shown to have teeth and hypobranchial muscles similar to those in extant chondrichthyans. Associated with the evolution of jaws was the evolution of a moveable neck, which allowed the first jawed vertebrates to raise their heads and increase the size of their mouths, making it more efficient for food and water intake. The evolution of jaws and associated musculature enabled gnathostomes to occupy new niches and to radiate, leading to the great diversity observed today. New fossil discoveries continue to populate the gnathostome stem, adding to our understanding of the early diversification of this successful group of vertebrates.