Fishes evolution

• Living gnathostomes

  • Sharks
  • Ray-finned fishes
  • Lobe-finned fishes
  • Amphibians
  • Reptiles (including birds)
  • Mammals
• Gnathostomes


  Named for their jaws, hinged structures that, especially with the help of teeth, enable them to grip food items firmly and slice them
• Placoderms


  Earliest gnathostomes in the fossil record, extinct lineages of armored vertebrates. Means plate-skinned.
• Acanthodians

  Emerged during the Silurian and Devonian periods
• Most sharks have a streamlined body and are swift swimmers, but they do not maneuver very well
• Continual swimming ensures that water flows into the shark’s mouth and out through the gills for gas exchange
• The largest sharks and rays are suspension feeders that consume plankton
• Shark eggs are fertilized internally
• Some species of sharks are oviparous, others are ovoviviparous, and a few are viviparous
• Most rays are bottom-dwellers that feed by using their jaws to crush molluscs and crustaceans
• Actinopterygii

  Ray-finned fishes, originated during the Silurian period, serve as a major source of protein for humans
• Sarcopterygii

  Originated during the Silurian period, key derived character is the presence of rod-shaped bones surrounded by a thick layer of muscle in their pectoral and pelvic fins
• Sarcopterygii groups


  • Actinistia
  • Dipnoi
• The coelacanths, a group of Actinistia, was thought to have become extinct 75 million years ago
• The second lineage of living lobe-fins, the lungfishes, is represented today by six species in three genera, all found in the Southern Hemisphere
• Condrichthes means cartilage fish, have a skeleton composed predominantly of cartilage.