Fish acquire armour
Jawless fish encase themselves in bony plates — the first vertebrate skeletons on the outside.
- When
- Known to
- ± 10 million years
- Era
- Ordovician, Paleozoic
Ostracoderms, armoured jawless fish, become widespread through the Ordovician, their heads and bodies sheathed in bony plates. Bone appears first as external armour rather than internal skeleton, most likely as protection against predators such as eurypterids and nautiloids. The mineralised tissues they evolve — dentine and enamel among them — are the same ones that later become teeth.