How and why

During the Devonian Period, some fish developed a number of important features that gave evolutionary advantages.

Many species became fast and efficient predators, due to the evolution of:

  • Teeth and jaws. These were essential for taking the step from sediment grazers and water filterers to plant and meat eaters.
  • Pairs of pectoral and pelvic fins. Together with a stronger spine, these were important for the evolution of rapid-swimming predatory fish species.
  • Bone tissue throughout the skeleton that was continually renewed, in ongoing adaptation to the demands placed on the skeleton.

These features are present in all modern four-footed vertebrates – although the bones of the fins have, of course, evolved into limbs. It is interesting to note that this development occurred in several fish groups, and had already begun during the Silurian Period.

The evolution of teeth and jaws appears to have been especially advantageous, as it occurred in most fish groups during almost the same time.

Pansarhaj. Bild: Nobu Tamura, cc-by-sa

A Devonian placoderm that resembles a modern fish
with a hard skeleton, jaws and paired fins.

Image: Nobu Tamura