A deep time perspective has little difficulty explaining these observed facts of the fossil record. Sea reptiles evolved from land reptiles during the Age of the Dinosaurs (Triassic – Cretaceous). Following their extinction, around the same time as the dinosaurs, the oceans lacked large animal predators other than sharks. With the diversification of mammals after the dinosaur age, some lineages, including one that became cetaceans, found conditions advantageous for adapting to life in the ocean. A deep time perspective also provides an explanation for how so many species could have existed.