of Europe), Baltica (the rest of Europe), and Siberia (Northern Asia). Devonian Period The Devonian spans from 419 million to 359 million years ago. Also informally known as the "Age of the Fish", the Devonian features a huge diversification in fish. Armored fish included jawless "agnathans", as well as jawed placoderms such as Dunkleosteus. The Devonian also saw a diversification of modern fish groups such as chondricthyans (sharks and kin), osteichthyans (ray-finned fish), and sarcopterygians (lobe-finned fish). One lineage of sarcopterygians evolved into the first four-limbed vertebrates, which would eventually become tetrapods. On land, plant groups diversified; the first trees and seeds evolved during this period. By the Middle Devonian, shrub-like forests of early plants existed: lycophytes, horsetails, ferns, and progymnosperm. This event also allowed the diversification of arthropod life as they took advantage of the new habitat. Near the end of the Devonian, 70% of all species became extinct in a sequence of mass extinction events, collectively known as the Late Devonian extinction. Carboniferous Period The Carboniferous spans from 359 million to 299 million years ago. Tropical swamps dominated the Earth, and the large amounts of trees created much of the carbon that became coal deposits (hence the name Carboniferous). About 90% of all coal beds were deposited in the Carboniferous and Permian periods, which represent just 2% of the Earth's geologic history. The high oxygen levels caused by these swamps allowed massive arthropods, normally limited in size by their respiratory systems, to proliferate. Tetrapods diversified during the Carboniferous, and one lineage acquired an amniotic egg which could survive outside of the water. These tetrapods, the amniotes, included the first reptiles and synapsids (mammal relatives). Throughout the Carboniferous, there was a cooling pattern, which eventually led to the glaciation of Gondwana as much of it was situated around the south pole. This event was known as the Permo-Carboniferous Glaciation and resulted in a major loss of area for coal forests, the Carboniferous rainforest collapse. Permian Period The Permian spans from 298 million to 251 million years ago and was the last period of the Paleozoic era. At its beginning, all continents came together to form the super-continent Pangaea, surrounded by one ocean called Panthalassa. The Earth was relatively dry compared to the Carboniferous, with harsh seasons, as the climate of the interior of Pangaea was not moderated by large bodies of water. Amniotes flourished and diversified in the new