Birds have lightweight skeletons in which many of the major bones are hollow. Unique to the skeleton of birds is the furculum, or wishbone. When in flight, the furculum not only aids the animal in breathing, but acts as a shock absorber against the great force of wing movement. Eggs are laid instead of the mother carrying the young inside her. Light skeletons, hollow bones, and of course, feathers.
Fish are a diverse group of animals that live and breathe in water.
Fish are recognized by their fins, scales, which serve as protection, and the streamline shape of their bodies, which aids them in moving through the water. All fishes are vertebrates and are equipped with gills for breathing. Over 25,000 species of fish have been identified, and we discover hundreds more each year. We can find fish in almost all waters of the planet, excluding only the harshest of water environments, such as the Dead Sea. Killifish living in the tropics of South America and Africa release their eggs, or spawn, as the dry season begins.