The face of vertebrate evolution

The development of the jaw is a key episode in vertebrate evolution, but the morphological gap between jawed and jawless vertebrates is so great that it is difficult to identify individual steps involved in the transition. The fossil record can help. Min Zhu and colleagues illuminate a step near the end of the process, in which modern jawed vertebrates such as sharks and bony fish emerge from a collection of jawed, armoured fishes known as placoderms. Most placoderms had jaws very unlike those of modern jawed vertebrates. Enter Entelognathus, a placoderm with full body armour but with jaw bones similar to those of modern bony fish: this the most primitive known creature with what we would recognize as a face.