Bird brains are wonderful structures. Indeed, “bird-brained” is an unusually poor insult, because the avian brain is one of the most complex seen in vertebrates. “Turtle-brained” might be a better insult in terms of neuroanatomy. That slight would be more hard-hitting if you meant to slander someone’s higher reasoning abilities. While bird brains are larger relative to body size than those of turtles, crocodiles, lizards and even some mammals, size is not the only thing that matters. Different parts of the brain are responsible for different functions. Deciphering the proportions of different parts of the brains of extinct animals can therefor give us insight into their biology.