One Jurassic stage is named for a mythical lover of the dawn
Most slices of geological time take their names from towns and quarries, but the last stage of the Jurassic honours Tithonus, the Trojan prince who fell in love with Eos, goddess of the dawn. Albert Oppel chose the name in 1865 because the stage runs straight into the dawn of the Cretaceous.
The period itself is named after the Jura Mountains along the French-Swiss border. Touring the region in 1795, Alexander von Humboldt recognised its limestones as distinct from similar rocks in southern Germany, though he wrongly judged them older, and in 1799 he called them Jura limestone. Alexandre Brongniart used the phrase Jurassic terrains in 1829, and ten years later Leopold von Buch split the sequence into Black, Brown and White Jurassic. Alcide d'Orbigny then carved it into ten stages between 1842 and 1852, seven of which survive in name though not in their original form.
Ammonites, coiled relatives of squid, are the key to dating these rocks. The first appearance of a particular species marks the start of a stage or a finer ammonite zone, and global correlation leans on standard European zones. That is why stage names read like an English and French road trip: Bathonian after Bath, Oxfordian after Oxford, Kimmeridgian after a Dorset village, Bajocian after Bayeux in Normandy.
The Jurassic lasted about 58 million years, from 201.4 to 143.1 million years ago. It opened with a mass extinction tied to enormous volcanic eruptions and, curiously, it is the only boundary between geological periods that has never been formally fixed at its end. Pangaea was splitting into Laurasia in the north and Gondwana in the south. The world was warmer than today, with no ice caps and forests reaching near the poles.
Life was reorganising. Dinosaurs took over the land from the crocodile-line reptiles that had shared it during the Triassic, and the first birds branched off from theropod dinosaurs. Crabs, modern frogs, salamanders and lizards made their first appearances, as did the earliest true mammals. In the seas swam ichthyosaurs and plesiosaurs, joined by the first modern sharks and rays, while pterosaurs ruled the air. Around 183 million years ago another volcanic episode starved parts of the oceans of oxygen, triggering a wave of extinctions.
Source: Jurassic
