Geologic Time Line of fossil records. Fossils from the Paleozoic period (approx. 541-252.17 million years ago) included the first skeletal elements, soft-bodied metazoans, animal traces, fish, and chordates. Sudden diversification of metazoan families, the first vascular land plants, amphibians, jaw fishes, reptiles, scale trees, and seed ferns. Finally at the end of this period a major extinction happens and reptiles diversify. Fossils from the mesozoic period (252 to 66 million years ago) include the first mammals, dinosaurs, birds, and flowering plants. Dinosaur's also diversify and then become extinct in this period. Fossils from the cenozoic period (current period 0-66 million years ago) include the diversification of mammals and the evolution of humans.