Asked by: Ben Dawson, Exeter
Some reptiles, notably snakes, don’t have ears at all. Those that do have a much simpler ear design than mammals, with the eardrum either flush with the side of the head or only slightly recessed. Around 260 million years ago, as mammal and reptile lineages first began to diverge, some of the bones of the reptile jaw evolved to form the specialised bones of the inner ear. This placed the eardrum much deeper into the head and probably favoured the evolution of an external ear structure to funnel the sound down towards it.