Editing Trilobite (section)

===Trilobite relatives===
Trilobites belong to the [[Artiopoda]], a group of extinct [[arthropod]]s morphologically similar to trilobites, though only the trilobites had heavily [[Mineralized tissues|mineralised]] exoskeletons. Thus, other artiopodans are typically only found in exceptionally preserved deposits, mostly during the Cambrian period.

The exact relationships of artiopods to other arthropods is uncertain. Some scholars consider them closely related to [[chelicerates]] (which include [[horseshoe crabs]], [[Sea spider|sea spiders]], and [[arachnids]]) as part of a clade called [[Arachnomorpha]], while others consider them to be more closely related to [[Mandibulata]] (which contains [[insects]], [[crustacean]]s and [[myriapods]]) as part of a clade called [[Antennulata]].<ref>{{Cite journal |last=Aria |first=Cédric |date=2022-04-26 |title=The origin and early evolution of arthropods |url=https://onlinelibrary.wiley.com/doi/10.1111/brv.12864 |journal=Biological Reviews |volume=97 |issue=5 |language=en |pages=1786–1809 |doi=10.1111/brv.12864 |pmid=35475316 |s2cid=248402333 |issn=1464-7931}}</ref>

[[Cladogram]] of Artiopoda including trilobites after Berks et al. 2023.<ref name=":02">{{Cite journal |last1=Berks |first1=H. O. |last2=Nielsen |first2=M. L. |last3=Flannery-Sutherland |first3=J. |last4=Nielsen |first4=A. T. |last5=Park |first5=T.-Y. S. |last6=Vinther |first6=J. |year=2023 |title=A possibly deep branching artiopodan arthropod from the lower Cambrian Sirius Passet Lagerstätte (North Greenland) |journal=Papers in Palaeontology |volume=9 |issue=3 |at=e1495 |doi=10.1002/spp2.1495 |s2cid=259253098 |doi-access=free|bibcode=2023PPal....9E1495B }}</ref>{{clade|{{clade
|1={{clade
|1=''[[Thulaspis]]'' [[File:Thulaspis diagram.jpg|100px]]
|2=''[[Squamacula]]''  [[File:S._clypeata.png|70px]]
}}
|2={{clade
|label1=Protosutura
|1={{clade
|1=''[[Zhiwenia]]''
|2=''[[Australimicola]]''
|3=''[[Acanthomeridion]]'' [[File:Acanthomeridion_diagram.jpg|100px]]
}}
|2={{clade
|label1=[[Vicissicaudata]]
|1={{clade
|1=''[[Sidneyia]]'' [[File:Sidneyia_inexpectans.png|100px]]
|2={{clade
|1=[[Cheloniellida]] [[File:20200415_Cheloniellon_calmani.png|70px]]
|2={{clade
|1=''[[Emeraldella]]'' [[File:Emeraldella_brutoni_reconstruction.png|70px]]
|2={{clade
|1=''[[Kodymirus]]'' [[File:Kodymirus_vagans.jpg|70px]]
|2={{clade
|1=''[[Eozetetes]]''
|2=[[Aglaspidida]] [[File:20240212_Aglaspis_spinifer.png|100px]]
}}}}}}}}}}
|label2=[[Trilobitomorpha]]
|2={{clade
|1={{clade
|1=''[[Retifacies]]'' [[File:Retifacies.jpg|100px]]
|2=''[[Pygmaclypeatus]]'' [[File:Pygmaclypeatus.png|100px]]
}}
|2={{clade
|1=[[Xandarellida]] [[File:Xandarella.png|70px]]
|2={{clade
|1=[[Nektaspida]] [[File:Naraoia magna reconstruction.png|70px]]
|2={{clade
|1=[[Conciliterga]] [[File:Kuamaia_lata.png|100px]]
|2={{clade
|1=''[[Kwanyinaspis]]'' [[File:Kwanyinaspis_final.svg|70px]]
|2={{clade
|1=''[[Phytophilaspis]]'' [[File:Phytophilaspis_outline.svg|70px]]
|2='''Trilobita''' [[File:Estonian_Museum_of_Natural_History_-_trilobite_-_Hydrocephalus.png|100px]]
}}}}}}}}}}}}}}}}}}|label1=[[Artiopoda]]}}

====Fossil record of early trilobites====
[[File:BLW Trilobite (Paradoxides sp.).jpg|thumb|right|[[Redlichiida]], such as this ''[[Paradoxides]]'', may represent the ancestral trilobites.]][[File:Fossil_Prochuangia_from_the_Cambrian_period_of_Darnjal_Formation,_Tabas,_Iran_02.jpg|thumb|Fossil [[Prochuangia]] from the Cambrian period of Darnjal Formation, Tabas, Iran]]
[[File:Scutelluid trilobite.jpg|thumb|right|''[[Meroperix]]'', from the Silurian of [[Wisconsin]]]]
[[File:Trilobite Walliserops trifurcatus.jpg|thumb|''[[Walliserops|Walliserops trifurcatus]]'', from Jebel Oufatene mountain near [[Fezzou, Morocco]]]]
The earliest trilobites known from the [[fossil record]] are [[Redlichiida|redlichiids]] and [[Ptychopariida|ptychopariid bigotinids]] dated to around 520{{nbsp}}million years ago.<ref name="lieberman02" /><ref name=Fortey00a>{{citation|title=Trilobite!: Eyewitness to Evolution|first=Richard|last=Fortey|author-link=Richard Fortey |year=2000|isbn=978-0-00-257012-1|publisher=HarperCollins|location=London}}</ref> Contenders for the earliest trilobites include ''Profallotaspis jakutensis'' (Siberia), ''Fritzaspis'' spp. (western US), ''Hupetina antiqua'' (Morocco)<ref name="Hollingsworth08">{{cite conference |conference=Fourth International Trilobite Conference, Toledo, June, 16-24, 2008 |last=Hollingsworth |first=J. S. |contribution=The first trilobites in Laurentia and elsewhere |editor=I. Rábano |editor2=R. Gozalo |editor3=D. García-Bellido |title=Advances in trilobite research |journal=Cuadernos del Museo Geominero, Nº 9 |publisher=Instituto Geológico y Minero de España |place=Madrid, Spain |year=2008 |isbn=978-84-7840-759-0 |url=http://www.igme.es/museo/trilo08/archivos/TRILOBITE.pdf |archive-url=https://web.archive.org/web/20150710041519/http://www.igme.es/museo/trilo08/archivos/TRILOBITE.pdf |url-status=dead |archive-date=July 10, 2015 }}</ref><ref name=Bushuev2014>{{cite journal|author=Bushuev E., Goryaeva I., Pereladov V.|year=2014|url=http://www.geology.cz/bulletin/fulltext/1406_Bushuev.pdf|title=New discoveries of the oldest trilobites ''Profallotaspis'' and ''Nevadella'' in the northeastern Siberian Platform, Russia|journal=Bull. Geosci.|volume=89|issue=2|page=347—364|doi=10.3140/bull.geosci.1406|archive-url=https://web.archive.org/web/20220319200546/http://www.geology.cz/bulletin/fulltext/1406_Bushuev.pdf|archive-date=2022-03-19|url-status=dead}}</ref> and ''Serrania gordaensis'' (Spain).<ref name="Linan-etal08">{{Citation |last1=Linan |first1=Eladio |last2=Gozalo |first2=Rodolfo |last3=Dies Alvarez |first3=María Eugenia |title=Nuevos trilobites del Ovetiense inferior (Cámbrico Inferior bajo) de Sierra Morena (España) |journal=Ameghiniana |year=2008 |volume=45 |issue=1 |pages=123–138 |url=http://www.scielo.org.ar/scielo.php?script=sci_abstract&pid=S0002-70142008000100008&lng=es&nrm=iso&tlng=en}}</ref> Trilobites appeared at a roughly equivalent time in [[Laurentia]], [[Siberia (continent)|Siberia]] and West [[Gondwana]].<ref name=Bushuev2014/><ref name="Holmes-2022">{{Cite journal |last1=Holmes |first1=James D. |last2=Budd |first2=Graham E. |date=2022-11-04 |title=Reassessing a cryptic history of early trilobite evolution |journal=Communications Biology |language=en |volume=5 |issue=1 |pages=1177 |doi=10.1038/s42003-022-04146-6 |issn=2399-3642 |pmc=9636250 |pmid=36333446}}</ref>

All Olenellina lack facial sutures (see [[#Facial sutures|below]]), and this is thought to represent the original state. The earliest sutured trilobite found so far (''[[Lemdadella]]''), occurs almost at the same time as the earliest Olenellina, suggesting the trilobites origin lies before the start of the Atdabanian, but without leaving fossils.<ref name="lieberman02" /> Other groups show secondary lost facial sutures, such as all [[Agnostina]] and some [[Phacopina]]. Another common feature of the Olenellina also suggests this suborder to be the ancestral trilobite stock: early protaspid stages have not been found, supposedly because these were not calcified, and this also is supposed to represent the original state.<ref name=Clowes06a>{{Citation|last=Clowes |first=Chris |title=Trilobite Origins |url=http://www.peripatus.gen.nz/Taxa/Arthropoda/Trilobita/TriOri.html |access-date=April 12, 2009 |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> Earlier trilobites may be found and could shed more light on their origins.<ref name="lieberman02" /><ref name="Jell03">{{Citation |last1=Jell |first1=P. |contribution=Phylogeny of Early Cambrian trilobites |editor=Lane, P. D. |editor2=Siveter, D. J. |editor3=Fortey, R. A. |series=Special Papers in Palaeontology|volume= 70 |title=Trilobites and Their Relatives: Contributions from the Third International Conference, Oxford 2001 |pages=45–57 |publisher=Blackwell Publishing & Palaeontological Association |year=2003 }}</ref><ref>{{cite web |url=http://www.trilobites.info/firsttrilos.htm |title=First Trilobites |author=Sam Gon III}}</ref>

Three specimens of a trilobite from Morocco, ''Megistaspis hammondi'', dated 478{{nbsp}}million years old contain fossilized soft parts.<ref>{{Cite news|url=http://news.nationalgeographic.com/2017/02/trilobite-fossils-guts-legs-footprints-morocco-paleontology-science|archive-url=https://web.archive.org/web/20170206160555/http://news.nationalgeographic.com/2017/02/trilobite-fossils-guts-legs-footprints-morocco-paleontology-science/|url-status=dead|archive-date=February 6, 2017|title=Found: Guts of 470-Million-Year-Old Sea Creature|date=2017-02-06|access-date=2017-02-07}}</ref><ref>{{cite journal |last1=Gutiérrez-Marco |first1=Juan C. |last2=García-Bellido |first2=Diego C. |last3=Rábano |first3=Isabel |last4=Sá |first4=Artur A. |date=2017-01-10 |title=Digestive and appendicular soft-parts, with behavioural implications, in a large Ordovician trilobite from the Fezouata Lagerstätte, Morocco |journal=Scientific Reports |language=en |volume=7 |doi=10.1038/srep39728 |issn=2045-2322 |pmc=5223178 |pmid=28071705 |page=39728|bibcode=2017NatSR...739728G }}</ref> In 2024, researchers discovered soft tissues and other structures including the [[Labrum (arthropod mouthpart)|labrum]] in well-preserved trilobite specimens from [[Cambrian Stage 4]] of Morocco, providing new anatomical information regarding the external and internal morphology of trilobites, and the cause of such extraordinary preservation is probably due to their rapid death after an underwater pyroclastic flow.<ref>{{cite journal|last1=El Albani |first1=A. |last2=Mazurier |first2=A. |last3=Edgecombe |first3=G. D. |last4=Azizi |first4=A. |last5=El Bakhouch |first5=A. |last6=Berks |first6=H. O. |last7=Bouougri |first7=E. H. |last8=Chraiki |first8=I. |last9=Donoghue |first9=P. C. J. |last10=Fontaine |first10=C. |last11=Gaines |first11=R. R. |last12=Ghnahalla |first12=M. |last13=Meunier |first13=A. |last14=Trentesaux |first14=A. |last15=Paterson |first15=J. R. |title=Rapid volcanic ash entombment reveals the 3D anatomy of Cambrian trilobites |year=2024 |journal=Science |volume=384 |issue=6703 |pages=1429–1435 |doi=10.1126/science.adl4540 |pmid=38935712 |bibcode=2024Sci...384.1429E }}</ref>