Mesozoic Era spans 250-65 million years ago. Geologists mark dinosaur periods based on fossil locations. Earth was joined into Pangaea during Triassic period
Birds evolved from theropod dinosaurs in Jurassic Period. Archaeopteryx was considered earliest bird for over century. Birds evolved independently from saurischian dinosaurs. Flight was first developed in early dromaeosaurids
Life began 4 billion years ago with prokaryotes. First animals appeared 665 million years ago in South Australia. Diploblasts evolved with two germ layers and photoreceptive eyes. Bilateral symmetry and cephalization appeared in urbilaterians
Fish have paired gonads, which can be partially or totally fused. Most male fish have two testes, with right side usually larger. Most female fish have two ovaries, some have only one. Fish eggs are jellylike and can develop throughout life
Fish evolved from filter feeders 535-0 Ma ago. First jawed fish appeared in Silurian, "Age of Fishes". Bony fish evolved after end-Devonian extinction. Teleosts (96% of fish) are bony fishes with protruding jaws
Mammals evolved from cynodonts during Late Triassic to Early Jurassic. First mammals appeared 225-0 million years ago. Modern diversity reached after dinosaur extinction 66 million years ago. Placentals diverged from other groups in Late Cretaceous