What is Devonian?
The '''Devonian''' is the fourth period of the [[Paleozoic]] [[era]] and the [[Phanerozoic]] [[eon]]. It lasted from about 419 million years ago (mya) to about 359 mya.<ref>Gradstein, Felix M; Ogg J.G. & Smith A.G. 2004. A geologic time scale. Cambridge: Cambridge University Press. {{ISBN|0-521-78673-8}}.</ref> It is named after [[Devon]]shire, [[England]], where rocks from this period were first studied. Sea levels were high, and there was a great variety of fish and other marine organisms.<ref>The Devonian is sometimes called the Age of Fish.</ref> The Devonian fish included the [[Agnatha]] (jawless fish), the [[Acanthodii]] (spiny fish), the [[Placoderm]]s (armoured fish), the [[Chondrichthyes]] (cartilaginous fish), and the early [[Osteichthyes]] (bony fish). The Devonian [[strata]] are divided into lower, middle and upper subdivisions. [[File:Tiktaalik BW.jpg|thumb|[[Tiktaalik]] was an [[Extinction|extinct]] [[tetrapodomorph]] that lived during the Devonian.]] During the Devonian the [[evolution]] of [[fish]] into [[tetrapod]]s occurred.<ref>see [[Tetrapod#fishapods]] for discussion and references.</ref> Various terrestrial [[arthropod]]s also became established. The first [[seed plant|seed-bearing plants]] spread across dry land, forming huge forests. The supercontinent of [[Gondwana]] was to the south, and the continent of [[Siberia]] to the north. The early form of the small continent of [[Euramerica]] was in between. The supercontinent [[Pangaea]] was just starting to form. By the late Devonian, the land had been colonized by plants and [[insects]]. In the oceans, massive reefs were built. Euramerica and Gondwana were beginning to converge into what would become [[Pangaea]]. == Period ended with extinctions == [[Plate tectonics|Tectonic]] and [[Volcano|volcanic]] activity was high. A series of [[List of extinction events|extinction event]]s occurred towards the end of the Devonian, including a major event at the Frasnian-Famennian boundary in the Late Devonian, about 364 mya. A major extinction o