The way people have been talking about Tiarajudens eccentricus, you would think that this 265 million year old cousin of ours was unique among herbivores for having saber-fangs. It was not, but it does raise the question of what makes a saber-tooth in the first place.

Over fifty million years before Tiarajudens, there was a great evolutionary split among small, lizard-like vertebrates. On the one side were the early diapsids – the starting point for the full diversity of reptiles – and on the other were the early synapsids; a group of unfamiliar creatures that underwent a major evolutionary radiation before the time of the dinosaurs and, today, is represented entirely by mammals. Since the anomodonts were one of