鱼石螈(D3C1)最早原始两牺类 amphibian QS59998S0nE Figure 1 1-73 The skeleton of Ichthyostega still retains the fishlike form of its cros sopterygian ancestors (From H. L. Levin. Life Through Time. Dubuque, lowa, william C Brown Co., 1975)鱼石螈(D3 -C1 )—最早原始两栖类 amphibian