The Blooming of March Spring. The Jurassic saga. Marine Life

The oceans had been massively depopulated by the Permian Extinction when as many as 95 percent of extant marine genera were wiped out by high carbon dioxide levels. Fossil fish from the Triassic Period are very uniform, which indicates that few families survived the extinction. The mid- to late Triassic Period shows the first development of modern stony corals and a time of modest reef building activity in the shallower waters of the Tethys near the coasts of Pangaea.


Early in the Triassic, a group of reptiles, the order Ichthyosauria, returned to the ocean. Fossils of early ichthyosaurs are lizard-like and clearly show their tetrapod ancestry. Their vertebrae indicate they probably swam by moving their entire bodies side to side, like modern eels. Later in the Triassic, ichthyosaurs evolved into purely marine forms with dolphin-shaped bodies and long-toothed snouts. Their vertebrae indicate they swam more like fish, using their tails for propulsion with strong fin-shaped forelimbs and vestigial hind limbs. These streamlined predators were air breathers and gave birth to live young. By the mid-Triassic, the ichthyosaurs were dominant in the oceans. One genus, Shonisaurus, measured more than 50 feet long (15 meters) and probably weighed close to 30 tons (27 metric tons). Plesiosaurs were also present but not as large as those of the Jurassic Period.