Early Jurassic

From Freepedia

For general context see Jurassic.

Lower Jurassic (also known as Lias) is the earliest of three epochs of Jurassic period. It saw much deposition of clay followed by limestone.

During this period, ammonoids, which had almost died out at the end-of-Triassic extinction, radiated out into a huge diversity of new forms with complex suture patterns (the ammonites proper). The ichthyosaurs and plesiosaurs appeared, with a number of families evolving. In the Toarcian, at the end of the Early Jurassic, they were joined by thalattosaurs or marine Crocodiles.

On land, a number of new types of dinosaurs - the heterodontosaurs, scelidosaurs, stegosaurs, and tetanurae, appeared, and joined those groups like the podokesaurs, prosauropods and the sauropods that had continued over from the Triassic. Accompanying them as small carnivores were the sphenosuchid and protosuchid crocodilians. In the air, new types of pterosaurs replaced those that had died out at the end of the Triassic. While in the undergrowth were various types of early mammals, as well as tritylodont mammal-like reptiles, lizard-like sphenodonts, and early Lissamphibians.

The names Lias was taken by a geologist from an English quarryman's dialect pronunciation of the word "layers".

Jurassic period
Lower/Early Jurassic		Middle Jurassic		Upper/Late Jurassic
Hettangian	Sinemurian	Aalenian	Bajocian	Oxfordian	Kimmeridgian
Pliensbachian	Toarcian	Bathonian	Callovian	Tithonian