Summary:
- The earliest vertebrates were jawless fish, similar to living hagfish.
- The first fish with a complete vertebral column evolved about 450 million years ago.
- Early bony fish evolved into modern ray-finned and lobe- finned fish.
- The phylogenetic tree in Figure below gives an overview of vertebrate evolution.
- As more data become available, new ideas about vertebrate Evolution emerge.
- The earliest vertebrate evolved almost 550 million years old.
- Until mammals and birds evolved, all vertebrate were ectothermic.