Placoderm
The placoderms (Placodermi: Greek = plated skin) were a class of armoured prehistoric fish, which lived from the mid Silurian to the end of the Devonian period. Their head and thorax were covered by armoured plates; the rest of the body was scaled or naked, depending on the species. Placoderms were among the first jawed fish, the Gnathostomata. A 380 million year old fossil of one species is the oldest-known example of live birth.