What is Silurian?
[[File:Cooksonia.png|thumb|''Cooksonia'', earliest vascular plant, middle Silurian]] The '''Silurian''' was the [[Period (geology)|period]] from the end of the [[Ordovician]], about 443.4 million years ago (mya) to the beginning of the [[Devonian]] period, about 419 mya. It is the third period of the [[Paleozoic]] [[era]] and the [[Phanerozoic]] [[eon]] and the shortest period in the Paleozoic. As with other [[Geology|geologic]] periods, the [[Rock (geology)|rock]] beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The beginning of the Silurian is set at a major [[extinction]] when 60% of marine species were wiped out, the [[End-Ordovician extinction event]]. == First terrestrial biota == The Silurian was the first period that produced [[fossil]]s on land that are macroscopic. That means you can see them without using a [[microscope]]. These fossils are [[moss]] forests along [[lakes]] and streams, and [[millipede]]s and [[scorpion]]s on land later in the period. The fossil record of [[Eurypterids]] (sea scorpions) reached its greatest extent in the middle Silurian, about 430 million years ago. The first fossil records of [[vascular plant]]s, appeared in the second half of the Silurian period. The earliest known representatives of this group are the ''Cooksonia'' (mostly from the northern hemisphere) and ''Baragwanathia'' (from Australia). A primitive Silurian land plant with [[xylem]] and [[phloem]] but no differentiation in root, stem or leaf, was much-branched ''Psilophyton''. This plant reproduced by [[spore]]s and respired through [[stomata]] on every surface, and probably [[photosynthesis|photosynthesized]] in every tissue exposed to light. Some evidence suggests the presence of primitive predatory arachnids and [[myriapod]]s in later Silurian rocks. Predatory [[invertebrates]] would indicate that simple [[food web]]s were in place which included non-predatory prey animals.<ref>Andrew J. Jeram, Paul A. Selden and Dianne Edwards