Ostracoderms existed in two major groups, the more primitive cephalaspids.
2.
This allowed placoderms to lift their heads, unlike ostracoderms.
3.
The first fossil fishes that were discovered were ostracoderms.
4.
Ostracoderms have heads covered with a bony shield.
5.
Other ostracoderms, such as the Galeaspida are now known to have a paired olfactory organ.
6.
Later, about 420 million years ago, the jawed fish evolved from one of the ostracoderms.
7.
Early fish from the fossil record are represented by a group of small, jawless, armored fish known as ostracoderms.
8.
Like other ostracoderms, " Ateleaspis " had a head shield similar to that of " Cephalaspis ".
9.
Current phylogenetic analysis using a large number of characteristics now place pteraspidomorphs as the sister-group of all other ostracoderms and the gnathostomes.
10.
One of the earliest known armoured agnathan ( " ostracoderm " ) vertebrate, " Arandaspis ", dates from the Middle Ordovician.
