One of the three Mesozoic periods: it lasted from 199.6 to 145.5 Ma ago, following the Triassic and preceding the Cretaceous. The Jurassic period is subdivided into eleven stages (Hettangian, Sinemurian, Pliensbachian, Toarcian, Aalenian, Bajocian, Bathonian, Callovian, Oxfordian, Kimmeridgian, and Tithonian), with clays, calcareous sandstones, and limestones being the most common rock types. Brachiopods, bivalves, and ammonites are abundant fossils, along with many other invertebrate stocks. Reptiles flourished on land and in the sea, but mammals were relatively insignificant and presumed to have been predominantly nocturnal. The first birds, including Archaeopteryx, appeared in the Late Jurassic.