# Asaphida

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{{Short description|Extinct order of trilobites}}
{{redirect-distinguish|Loganellidae|Loganelliidae}}
{{Automatic taxobox
| fossil_range = {{fossil_range|Middle Cambrian|Silurian}}
| image = Asaphus.jpg
| image_caption = ''[Asaphus lepidurus](/source/Asaphus_lepidurus)''
| taxon = Asaphida
| authority = [Fortey](/source/Richard_Fortey) & Chatterton, 1988
| subdivision_ranks = Superfamilies
| subdivision = *[Anomocaroidea](/source/Anomocaroidea)
*[Asaphoidea](/source/Asaphoidea)
*[Cyclopygoidea](/source/Cyclopygoidea)
*[Dikelocephaloidea](/source/Dikelocephaloidea)
*[Remopleuridoidea](/source/Remopleuridoidea)
*[Trinucleioidea](/source/Trinucleioidea)?
}}

'''Asaphida''' is a large, morphologically diverse [order](/source/order_(biology)) of [trilobite](/source/trilobite)s found in marine [strata](/source/Stratum) dated from the Middle [Cambrian](/source/Cambrian) until their extinction during the [Silurian](/source/Silurian). Asaphida contains six [superfamilies](/source/Superfamily_(zoology)) (Anomocaroidea, Asaphoidea, Cyclopygoidea, Dikelocephaloidea, Remopleuridoidea and Trinucleioidea), but no [suborders](/source/suborders). Asaphids comprise some 20% of described [fossil](/source/fossil) trilobites.{{Citation needed|date=December 2024}}

In 2020, the superfamily [Trinucleioidea](/source/Trinucleioidea) was proposed to be raised to an order ([Trinucleida](/source/Trinucleioidea)) and removed from Asaphida.<ref>{{Cite journal |last1=Bignon |first1=Arnaud |last2=Waisfeld |first2=Beatriz G. |last3=Vaccari |first3=N. Emilio |last4=Chatterton |first4=Brian D. E. |date=2020-07-02 |title=Reassessment of the Order Trinucleida (Trilobita) |url=https://doi.org/10.1080/14772019.2020.1720324 |journal=Journal of Systematic Palaeontology |volume=18 |issue=13 |pages=1061–1077 |doi=10.1080/14772019.2020.1720324 |bibcode=2020JSPal..18.1061B |s2cid=212995185 |issn=1477-2019|url-access=subscription |hdl=11336/145642 |hdl-access=free }}</ref>

==Morphology==
[[File:Asaphellus_fossil_from_Mila_formation,_Ordovician_period,_Damghan,_Iran_01.jpg|thumb|''[Asaphellus](/source/Asaphellus)'' sp.]]
The Asaphids generally have [cephalon](/source/cephalon_(arthropod_anatomy)) (head) and [pygidium](/source/pygidium) (tail) parts similar in size, and most species have a prominent median ventral suture. Heads are often flat, and carapace furrows in the head area are often faint or not visible. Thoracic segments typically number 5 - 12, though some species have as few as two and some as many as 30. They also generally have a wide doublure, or rim, that surrounds the cephalon. This causes some specimens to be described as having a characteristic "snowplow" shaped cephalon. When present, eyes are typically large.

[[File:Trilobite2.jpg|thumb|left|''[Asaphus kowalewski](/source/Asaphus_kowalewski)'']]

One Asaphida line, the superfamily Asaphoidea, shows a continuous [evolution](/source/evolution) of eyestalks, from individuals with stubby eyes to ''[Asaphus kowalewskii](/source/Asaphus_kowalewskii)'', a trilobite with long [eyestalk](/source/eyestalk)s. This line is found in the Middle Ordovician Asery Level deposits of the [Volkhov River](/source/Volkhov_River) region near [Saint Petersburg](/source/Saint_Petersburg), [Russia](/source/Russia). During the Ordovician, the region that is now Eastern [Europe](/source/Europe) was a shallow inland sea. This eyestalk development is believed to be an adaptation to changes in turbidity during this time, with eye-stalked trilobites like ''A. kowalewski'' presumably arising in a time of increased turbidity. One thought is that this trilobite may have lain in wait for prey buried in the bottom [sediment](/source/sediment) with only its periscope eyestalks protruding.

The major extinction event marking the end of the Ordovician Period reduced the diversity of all trilobite orders with most asaphid families disappearing. The only surviving asaphids were members of superfamily [Trinucleioidea](/source/Trinucleioidea), and they too disappeared before the end of the [Silurian](/source/Silurian) Period.
[[File:Damghan_Ampyx_ghobadipour_fossil_from_Lashkark_Formation,_Ordovician,_Damghan,_Iran.jpg|thumb|''[Damghanampyx ghobadipour](/source/Damghanampyx)'' ]]

==Taxonomy==
The following superfamilies and families are included:<ref>{{cite web |url=http://www.trilobites.info/ordasaphida.htm |title=Order Asaphida |author=S. M. Gon III |access-date=9 July 2018}}</ref>
{{Div col|colwidth=25em}}
*Superfamily [Anomocaroidea](/source/Anomocaroidea)
**[Andrarinidae](/source/Andrarinidae)
**[Anomocarellidae](/source/Anomocarellidae)
**[Anomocaridae](/source/Anomocaridae)
**[Aphelaspididae](/source/Aphelaspididae)
**[Parabolinoididae](/source/Parabolinoididae)
**[Pterocephaliidae](/source/Pterocephaliidae)
*Superfamily [Asaphoidea](/source/Asaphoidea)
**[Asaphidae](/source/Asaphidae)
**[Ceratopygidae](/source/Ceratopygidae)
*Superfamily [Cyclopygoidea](/source/Cyclopygoidea)
**[Cyclopygidae](/source/Cyclopygidae)
**[Nileidae](/source/Nileidae)(?)
**[Taihungshaniidae](/source/Taihungshaniidae)
*Superfamily [Dikelocephaloidea](/source/Dikelocephaloidea)
**[Dikelocephalidae](/source/Dikelocephalidae)
**[Eurekiidae](/source/Eurekiidae)
**[Ptychaspididae](/source/Ptychaspididae)
**[Saukiidae](/source/Saukiidae)
*Superfamily [Remopleuridioidea](/source/Remopleuridioidea)
**[Auritamidae](/source/Auritamidae)
**[Bohemillidae](/source/Bohemillidae)
**[Hungaiidae](/source/Hungaiidae)
**[Idahoiidae](/source/Idahoiidae)
**[Remopleurididae](/source/Remopleurididae)
*Superfamily [Trinucleioidea](/source/Trinucleioidea) ?
**[Alsataspididae](/source/Alsataspididae)
**[Dionididae](/source/Dionididae)
**[Liostracinidae](/source/Liostracinidae)
**[Raphiophoridae](/source/Raphiophoridae)
**[Trinucleidae](/source/Trinucleidae)
*''[incertae sedis](/source/incertae_sedis)''
**[Rhyssometopidae](/source/Rhyssometopidae) (includes Mapaniidae, Plectriferidae)
**[Monkaspididae](/source/Monkaspididae) (Chelidonocephalidae ?)
{{div col end}}

==References==
{{Reflist}}

{{Taxonbar|from=Q220877}}

Category:Asaphida
Category:Cambrian trilobites
Category:Ordovician trilobites
Category:Silurian trilobites
Category:Trilobite orders
Category:Cambrian first appearances
Category:Silurian extinctions

{{Asaphida-stub}}

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Adapted from the Wikipedia article [Asaphida](https://en.wikipedia.org/wiki/Asaphida) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Asaphida?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.