The teeth had been discovered many years ago. But, until recently, no fossil of the intact animal had been identified. In 1983, an extraordinarily well preserved fossil of the intact animal, showing a slender soft-bodied animal, was found near Edinburgh, Scotland. Since then, more conodont fossils have been found in Scotland and South Africa. Well, one theory for origin of the craniates is that they were formed by phaedomorphosis , the retention of juvenile characteristics by adults.
Some researchers believe that the first craniates developed by neoteny.
In this view, the first adult craniates looked a lot like primitive larval chordates, except that they are sexually mature. The agnathans , jawless vertebrates, are the earliest known craniates. Most of the nice Ordovician fossils were collected as recently as the 1980's from sites near Alice Springs in central Australia. A very important group of agnathans are the ostracoderms which also appeared during the Ordovician. These took on a lot of forms.