Trilobite Order Asaphida

The most conspicuous morphological feature of the Asaphid trilobites is the smooth and isopygous (similar in size) cephalon

Trilobite Taxonomy	Trilobite Phylogeny
Phylum Arthropoda Subphylum Chelicerata or Subphylum Schizoramia * Superclass Arachnomorpha * Class Trilobita Order Agnostida Order Redlichiida Order Corynexochida Order Phacopida Order Lichida Order Proetida Order Harpetida Order Ptychopariida Order Asaphida Order Odontopleurida Order Nectaspida Trilobite Relatives	o Arthropoda `--o Trilobita |?-Agnostida |?-Eodiscina `--+--o Redlichiida | |--Olenellina | `--Redlichiina |--Corynexochida |--Phacopida |--Lichida |--Odontopleurida `--o Librostoma |--Proetida |--Harpetida |--Ptychopariida `--Asaphida
* Different taxonomies are found, most recently with trilobites contained in Superclass Arachnomorpha in Subphylum Schizoramia.

and pygidium, an evolutionary adaptation called effacement believed to have helped trilobites more easily burrow into sediment to achieve stealth. Another theory is that the smoothing of the exoskeleton streamlined the trilobite for locamotion. Effacement is also evident among the Agnostids, and Suborder Illaenina of Order Corynexochida. The Asaphids appeared in the Middle Cambrian and persisted to the Lower Silurian. Order Asaphida comprises six Superfamilies: Anomocaroidea; Asaphoidea; Cyclopygoidea; Trinucleioidea; Dikelokephaloidea; and Remopleuridoidea listed at the bottom of this page. The order contains a very large morphological diversity and number of species; in fact, some 20% of known species.

The major extinction event concluding the Ordovician Period markedly reduced trilobite diversity across all the orders. Among the Asaphids, only some members of superfamily Trinucleioidea survived, and they too met extinction near the end of the Silurian.

Phylum Arthropoda Subphylum Chelicerata Class Trilobita Order Asaphida Suborder Asaphina Superfamily Anomocaroidea Family Andrarinidae Family Anomocarellidae Family Anomocaridae Family Aphelaspididae Family Parabolinoididae Family Pterocephalidae Superfamily Asaphoidea Family Asaphidae Family Ceratopygidae Superfamily Cyclopygoidea Family Cyclopygidae Family Nileidae Family Taishunghaniidae Superfamily Dikelokephaloidea Family Dikelokephalidae Family Eurekiidae Family Loganellidae Family Ptychaspididae Family Saukiidae Superfamily Remopleuridioidea Family Auritamiidae Family Bohemillidae Family Hungaiidae Family Idahoiidae Family Remopleurididae Superfamily Trinucleioidea Family Alsataspididae Family Dionididae Family Liostracinidae Family Raphiophoridae Family Trinucleidae Also see: Asaphida families and genera		Superfamily Anomocaroidea
		Housia sp. Superfamily Anomocaroidea Family Pterocephaliidae Upper Cambrian Radium, British Columbia	Pterocephalia norfordi Superfamily Anomocaroidea Family Pterocephaliidae Upper Cambrian Cranbrook, British Columbia
		Glyphaspis capella Superfamily Anomocaroidea Family Anomocarellidae Middle Cambrian Wolsey Formation, Montana
Superfamily Asaphoidea
Isoteloides flexus (rare) Superfamily Asaphoidea Family Asaphidae Ordovician Fillmore Formation, Millard County, Utah	Megistaspis triangularis Superfamily Asaphoidea Family Asaphidae Lower Ordovician Wolchow river, Russia	Homotelus florencevillensis Superfamily Asaphoidea Family Asaphidae Subfamily Isotelinae Upper Ordovician Clayton County, Iowa	Ptyocephalus yersini Superfamily Asaphoidea Family Asaphidae Subfamily Ptyocephalinae Ordovician Fillmore Formation Millard County, Utah
Niobe schmidti Superfamily Asaphoidea Family Asaphidae Middle Ordovician Wolchow River, Russia	Pseudoasaphus tecticaudatus Superfamily Asaphoidea Family Asaphidae Middle Ordovician Wolchow River, Russia	Isotelus gigas Superfamily Asaphoidea Family Asaphidae Ordovician Lindsay Formation, Ontario, Canada	Lachnostoma latucelsum Superfamily Asaphoidea Family Asaphidae Middle Cambrian Ninemile Formation, Nevada
Asaphus cornutus Superfamily Asaphoidea Family Asaphidae Middle Ordovician Wolchow River, Russia	Asaphus expansus Superfamily Asaphoidea Family Asaphidae Lower Ordovician Wolchow River, Russia	Asaphus punctatus Superfamily Asaphoidea Family Asaphidae Middle Ordovician Wolchow River, Russia	Asaphus kowalewskii Superfamily Asaphoidea Family Asaphidae Middle Ordovician Wolchow River, Russia
Asaphus cornutus Superfamily Asaphoidea Family Asaphidae Middle Ordovician Wolchov River, Russia	Pseudogygites latimarginatus Family Asaphidae Upper Ordovician Lower Whitby Formation, Ontario, Canada	Cyclopyge bohemica Superfamily Asaphoidea Ceratopygidae Middle Ordovician Czech Republic
Superfamily Trinucleioidea
Nankinolithis sp. Superfamily Trinucleoidea Family Trinucleidae Ordovician El Kaid Errami, Morocco	Paratrinucleus acervulosus Family Trinucleidae Upper Ordovician Blacksburg, Virginia	Onnia superba Death Assemblage Superfamily Trinucleoidea Family Trinucleidae Middle Devonian Blekos, Morocco	Salterolithus caractaci Superfamily Trinucleoidea Family Trinucleidae Upper Ordovician Caradoc Series, Harnage (Shales) Formation, Welshpool, England
Raphiophorus parvulus Family Raphiophoridae Upper Silurian Shropshire, United Kingdom	Cnemidopyge bisecta Family Raphiophoridae Upper Ordovician Wales, United Kingdom	Lochodomas volborthi Superfamily Trinucleoidea Family Trinucleidae Ordovician Wolchow River, Russia	Deanaspis goldfussi Superfamily Trinucleoidea Family Trinucleidae Ordovician Bohemia Czech Republic

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