Sea levels dropped considerably, while the remains of Gondwanaland rotated 
Sea levels dropped considerably, while the remains of Gondwanaland rotated clockwise and moved northward to collide with Laurasia, and the Caledonian-Acadian orogeny began. During this geologic period, psilophytes and other vascular plants began a land invasion. Also, the first jawed fishes appeared. First extensively studied by Roderick Murchison, who named it after an ancient Celtic tribe, FTP, identify this period of the Paleozoic era that lasted from 438 to 408 million years ago and falls between the Ordovician and Devonian periods.
Sea levels dropped considerably, while the remains of Gondwanaland rotated clockwise and moved northward to collide with Laurasia, and the Caledonian-Acadian orogeny began.
{Silurian} period