<Table> <Tr> <Td> </Td> <Td> <P> † Pteraspidomorphi (jawless fishes) </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> <P>? † Thelodonti (jawless fishes with scales) </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> unnamed </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <P>? † Anaspida (jawless ancestors of lampreys) </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> unnamed </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <P> † Galeaspida (jawless fishes with bone head shields) </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> unnamed </Td> <Td> <Table> <Tr> <Td> </Td> <Td> <P>? † Pituriaspida (armoured jawless fishes with large rostrums) </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> <P> † Osteostraci (bony armoured jawless fish with bone head shields) </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> <Tr> <Td> </Td> <Td> <P> Jawed vertebrates → continued in section below </P> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> <P> † Pteraspidomorphi (jawless fishes) </P> </Td> </Tr> <P> † Pteraspidomorphi (jawless fishes) </P> <Tr> <Td> </Td> <Td> <P>? † Thelodonti (jawless fishes with scales) </P> </Td> </Tr>

Two adaptations that enabled early fishes to dominate the oceans