Early tetrapods probably evolved from lobe-finned fishes able to use their muscular fins to take advantage of the predator-free and food-rich environment of the new wetland ecosystems. n, d-, d-/ dih-VOH-nee-n, d-, deh-) is a geologic period and system of the Paleozoic, spanning 60.3 million years from the end of the Silurian, 419.2 million years ago (Mya), to the beginning of the Carboniferous, 358.9 Mya. Forests and the coiled shell-bearing marine organisms known as ammonites first appeared early in the Devonian. [41], By the Devonian Period, life was well underway in its colonization of the land. [27][28][32], Sea levels in the Devonian were generally high. This eventually caused the formation of complex soil and more stable habitats. Causes of the extinctions include global cooling, including glaciations in the south polar area of Gondwana, and anoxia (oxygen loss) in the oceans. When did the Silurian period start and end? Brachiopods (ToL: Brachiopoda