Teeth play a central role in the ecology of most vertebrates – for catching prey, processing food and even attracting a mate. It’s no surprise that scientists such as ourselves have long been interested in how teeth first evolved. For many years we regarded shark teeth, with their conveyor belt system of tooth replacement, as ancestral models for teeth. But recent advances in our field of research revealed that a group of spiny fishes known as the acanthodians were the first ancestors of modern-day sharks. We decided to dive in and make a detailed study of the teeth of acanthodians.