Fossil evidence refutes notion that ancient lampreys had teeth

Nature : It has long been thought that the hard spurs inside the mouths of early conodonts—ancient, jawless eel-like animals that lacked either an internal or external skeleton—were the precursors to vertebrate teeth. But recent work by Philip Donoghue at the University of Bristol in the UK and colleagues has revealed that the tooth-like structures most probably evolved instead into the bony, protective exoskeleton of early fish. In that case, vertebrate teeth evolved later, from the skeleton. Although the bony spurs grew in early conodonts’ mouths much like teeth grow in modern animals, x-ray tomographic microscopy of their internal structure shows they lacked enamel—an essential element of teeth. According to the researchers’ study published online in Nature, “The hypothesis that teeth evolved before jaws and the inside-out hypothesis of dental evolution must be rejected.”