Editing Trilobite (section)

====Ordovician====
[[File:Worlds largest trilobite.jpg|thumb|Cast of ''[[Isotelus|Isotelus rex]]'', the largest-known trilobite, from the middle to upper [[Ordovician]] of [[North America]]]]
[[File:Trilobite Ordovicien 8127.jpg|thumb|''[[Cheirurus]]'' sp., middle [[Ordovician]] age, [[Volkhov River]], [[Russia]] ]]
The Early [[Ordovician]] is marked by vigorous radiations of articulate brachiopods, bryozoans, bivalves, echinoderms, and graptolites, with many groups appearing in the fossil record for the first time.<ref name="Clarkson98" /> Although intra-species trilobite diversity seems to have peaked during the Cambrian,<ref name="webster07">{{Citation |first=Mark |last=Webster |title=A Cambrian peak in morphological variation within trilobite species |journal=[[Science (journal)|Science]] |volume=317 |pages=499–502 |year=2007 |doi=10.1126/science.1142964 |pmid=17656721 |issue=5837|bibcode = 2007Sci...317..499W |s2cid=36290256 |doi-access= }}</ref> trilobites were still active participants in the Ordovician radiation event, with a new fauna taking over from the old [[Cambrian]] one.<ref name="Adrain98" /> [[Phacopida]] and [[Trinucleioidea]] are characteristic forms, highly differentiated and diverse, most with uncertain ancestors.<ref name="Clarkson98" /> The Phacopida and other "new" [[clade]]s almost certainly had Cambrian forebears, but the fact that they have avoided detection is a strong indication that novel morphologies were developing very rapidly.<ref name="Clowes06a" /> Changes within the trilobite fauna during the Ordovician foreshadowed the mass extinction at the end of the Ordovician, allowing many families to continue into the [[Silurian]] with little disturbance.<ref name=Adrain98>{{Citation |last1=Adrain |first1=Jonathan M. |last2=Fortey |first2=Richard A. |author-link2=Richard Fortey |last3=Westrop |first3=Stephen R. |title=Post-Cambrian trilobite diversity and evolutionary faunas |journal=[[Science (journal)|Science]] |volume=280 |year=1998 |doi=10.1126/science.280.5371.1922 |pmid=9632387 |issue=5371 |pages=1922–5|bibcode = 1998Sci...280.1922A |url=http://doc.rero.ch/record/14799/files/PAL_E1948.pdf }}</ref> Ordovician trilobites were successful at exploiting new environments, notably [[reef]]s. The Ordovician mass extinction did not leave the trilobites unscathed; some distinctive and previously successful forms such as the [[Telephinidae]] and [[Agnostida]] became extinct. The Ordovician marks the last great diversification period amongst the trilobites: very few entirely new patterns of organisation arose post-Ordovician. Later evolution in trilobites was largely a matter of variations upon the Ordovician themes. By the [[Ordovician-Silurian extinction events|Ordovician mass extinction]], vigorous trilobite radiation has stopped, and gradual decline is foreshadowed.<ref name="Clarkson98" /> The Ordovician marks the apex of trilobite morphological and species diversity.<ref name=":0" />

Some of the genera of Trilobites appearing in the Ordovician include:<ref name="PREHISTORIC LIFE" />

*''[[Cyclopyge (trilobite)|Cyclopyge]]'' (Early to Late Ordovician)
*''[[Selenopeltis]]'' (Early to Late Ordovician)
*''[[Parabolina]]'' (Early Ordovician)
*''[[Cheirurus]]'' (Middle Ordovician)
*''[[Eodalmanitina]] ''(Middle Ordovician)
*''[[Trinucleus]]'' (Middle Ordovician)
*''[[Triarthrus]]'' (Late Ordovician)