Page 57 - Curriculum Visions Dynamic Book. To close the book, close the window or tab.

Triassic. It was the time when the archosaurs, or ruling reptiles, evolved. The archosaurs include dinosaurs, birds and crocodiles. The first dinosaurs belong to the Late Triassic, as do the ichthyosaurs, marine reptiles that were shaped like dolphins. They were the largest animals in the Triassic world, reaching 9 metres
in length. Plesiosaurs that looked like turtles also developed. The mammals that emerged in the Triassic Period were small, about mouse sized.
At the end of the Triassic Period, there was yet another mass extinction, less severe than at the end of the Permian Period, but nevertheless a quarter of all families became extinct.
The Jurassic Period
(Below) Jurassic: vertebra from a dinosaur.
135 million
to 190 million years ago
Conifers, ammonoids, belemnoids common in oceans, dinosaurs common on land. First appearance of crocodiles, flying reptiles, and birds
During this period the surviving species began to diversify again. Ammonoids again flourished and became important index fossils. Coral reefs developed, and echinoids flourished. Squid-like belemnites also developed widely, reaching as much as 2 metres in length.
Land plants again flourished, and coniferous
plants again accumulated in swamps to form important coal deposits.
Reptiles were still the dominant group of land animals despite their setback at the end of the Triassic Period. Stegosaurus is a member of an order of dinosaurs that evolved during the Jurassic Period. They are distinctive dinosaurs because of the row
of triangular plates down their spines.
In the seas, ichthyosaurs continued to dominate, growing to 15 metres long. By the end of the Jurassic Period, they had been overtaken in importance by the similar-sized plesiosaurs.
During the Jurassic Period the first flying reptiles emerged. These are the pterosaurs, featherless but growing to an enormous size, although in the Jurassic
(Below) Jurassic belemnite.
57