ในช่วงเริ่มมหายุค, รูปแบบของสิ่งมีชีวิตทั้งหมดจะถูกจำกัดอยู่แค่แบคทีเรีย, สาหร่ายทะเล, ฟองน้ำทะเล และสิ่งมีชีวิตจำพวก Ediacaran fauna
At the start of the era, all life was confined to bacteria, algae, sponges and a variety of somewhat enigmatic forms known collectively as the Ediacaran fauna. A large number of body plans appeared nearly simultaneously at the start of the era -- a phenomenon known as the Cambrian Explosion. There is some evidence that simple life may already have invaded the land at the start of the Paleozoic, but substantial plants and animals did not take to the land until the Silurian and did not thrive until the Devonian. Although primitive vertebrates are known near the start of the Paleozoic, animal forms were dominated by invertebrates until the mid-Paleozoic. Fish populations exploded in the Devonian. During the late Paleozoic, great forests of primitive plants thrived on land forming the great coal beds of Europe and eastern North America. By the end of the era, the first large, sophisticated reptiles and the first modern plants (conifers) had developed.
