The first period of the Mesozoic era, the Triassic spanned from 250 to 200 million years ago but was only named in 1834 by German geologist Friedrich von Alberti, after the three (tri) distinctive rock layers common to much of northwestern Europe. During the lower Triassic almost all the planet's land mass consisted of one giant supercontinent called Pangaea. In the middle Triassic, the landmass began to gradually drift apart, forming the Tethys Ocean. Fish, reptiles and ammonites swam in the ocean and the first species of modern coral came into existence. Life on the hot and dry land was dominated by vertebrates called therapsids while, towards the end of the period, dinosaurs began to appear.
