This is a primitive amphibian. Because the enamel layer of teeth is labyrinthine in cross section, it is called Amphibia, and because of its solid skull structure, it is also called Cephalopoda. Save-sode-rberg, a ichthyosaur, produced in the Devonian old red sandstone in Greenland, can be taken as a representative. The body length is about 1m, and the skull length is about 20cm. It is tall and narrow, and the remaining branchial cover bone is covered with tiny scales on the body surface, and a fish-shaped tail fin is dragged at the back of the body. The structure of the skull, the characteristics of teeth and the shape of the spine are very similar to those of the finfish. However, it has limbs, articular processes on the spine (animals can bend and move), and the connection between the shoulder strap and the skull has been lost (fish are connected and cannot move freely), which shows that it can move freely and adapt to land life.