17) Permian-Triassic mass extinction

Artists impression of a dominant land vertebrate of the early Triassic, Lystrosaurus, a pig-sized herbivorous dicynodont therapsid. Image credit: Julio Lacerda/ Earth Archives

235 million years ago sees the end of the Permian period when the 4th and greatest mass extinction of life on Earth takes place. Trilobites and many other families of species disappear entirely and some 95% of the species of that time become extinct. The descendents of the surviving 5% radiate forth in dazzling creativity and the ancestors of dinosaurs emerge. For 170 million years these creatures flourish. Dinosaurs, sometimes as large as 40 meters, are social animals that often travel and hunt in groups. Dinosaurs develop a behavioural novelty unknown previously in the reptilian world – parental care. They carefully bury their eggs and stay with the young after they hatch, nurturing them toward independence.