Editing Trilobite (section)

====Facial sutures====
Facial or cephalic sutures are the natural fracture lines in the [[Cephalon (arthropod head)|cephalon]] of trilobites. Their function was to assist the trilobite in shedding its old exoskeleton during [[ecdysis]] (or molting).<ref name="trilo">{{Citation|author=Riccardo Levi-Setti|title =Trilobites|publisher =University of Chicago Press|year =1995|isbn =978-0-226-47452-6|url=https://books.google.com/books?id=rRyHMz-FkJUC}}</ref>

All species assigned to the [[suborder]] [[Olenellina]], that became extinct at the very end of the Early [[Cambrian]] (like ''[[Fallotaspis]]'', ''[[Nevadia]]'', ''[[Judomia]]'', and ''[[Olenellus]]'') lacked facial sutures. They are believed to have never developed facial sutures, having pre-dated their evolution. Because of this (along with other primitive characteristics), they are thought to be the earliest ancestors of later trilobites.<ref name="peri"/><ref name="lieberman02">{{Citation |last=B. S. |first=Lieberman |title=Phylogenetic analysis of some basal early Cambrian trilobites, the biogeographic origins of the eutrilobita, and the timing of the Cambrian radiation |journal=[[Journal of Paleontology]] |volume=76 |edition=4 |pages=692–708 |year=2002 |doi=10.1666/0022-3360(2002)076<0692:PAOSBE>2.0.CO;2 |issue=4}}</ref>

Some other later trilobites also lost facial sutures secondarily.<ref name="peri">{{cite web|url=http://www.peripatus.gen.nz/taxa/arthropoda/trilobita/TriOri.html |title=Trilobite Origins |author=Chris Clowes |date=April 15, 2006 |publisher=Peripatus |access-date=April 13, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110514222917/http://www.peripatus.gen.nz/Taxa/Arthropoda/Trilobita/TriOri.html |archive-date=May 14, 2011 }}</ref> The type of sutures found in different species are used extensively in the [[Taxonomy (biology)|taxonomy]] and [[phylogeny]] of trilobites.<ref name="gon"/>