Читать книгу Oceans For Dummies - Joseph Kraynak - Страница 58

The Triassic period (from 251.9 to 201.3 million years ago) was a time of rebuilding. After the Great Dying, few creatures remained. (Talk about a shrinking dating pool!) So, who was left? Temnospondyls (early amphibians) and therapsids (early relatives of mammals) made the cut, as did some fish, including some small sharks, and some mainly amphibious marine reptiles. Most animals living in shells fared poorly due to ocean acidification, which hinders the ability to form shells (more on that later). Hinged brachiopods, crinoids (sea lilies), and some ammonites (early mollusks) did okay.

During this period of rebuilding:

 The first ichthyosaurs (fishlike reptiles) evolve, probably from terrestrial ancestors that returned to the ocean; for example, the cartorhynchus (say that three times fast) has flippers like a seal and a tail like a lizard. Ichthyosaurs were predators, feeding on fish, shellfish, reptiles, and other ichthyosaurs. Some were ram feeders, like today’s whale shark, swimming toward their prey with mouth open to engulf the prey and the water around it. Others could crush shells or bore into them.

 Archosaurs (which means ruling reptiles) appeared on the scene. Broadly classified as reptiles, this group includes all extinct dinosaurs along with birds and crocodiles.

 The archosaurs split into two groups: Saurischia (lizard-hipped) and Ornithischia (bird-hipped).

 The plesiosaurs arrive — large marine reptiles with four flippers, a long neck, and a long tail (see Figure 3-5).

Source: National Park Service, Public Domain

FIGURE 3-5: An average, everyday plesiosaur.

This period abruptly ceased with the End-Triassic Mass Extinction, also known as the Triassic-Jurassic (T-J) Extinction event. Around the same time, Pangea started to break apart, with North America drifting off first. These were triggered by massive shifts in the tectonic plates which caused an enormous spike in volcanic activity and a resulting increase in greenhouse gasses, which really cranked up the heat. This particular mass extinction caused the loss of the temnospondyls (sort of like salamanders), therapsids (mammal-like reptiles), and most ichthyosaurs (though some larger species survived).