From the 20-foot-long jawbones of the filter-feeding blue whale to the short, but bone-crushing, jaws of the hyena and the delicate chin bones of a human, the pair of lower jawbones characteristic of mammals have evolved with amazing variation.
But at first glance, having a single bone on each side of the head — which creates a stiff lower jaw, or mandible — doesn’t appear to give mammals an advantage over other vertebrates, which have at least two and as many as 11 bones comprising each side of the lower jaw.