The Phacopina comprise a suborder of the

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

Phacopida Phacopida ("lens-face") is an order of trilobites that lived from the Late Cambrian to the Late Devonian. It is made up of a morphologically diverse assemblage of taxa in three related suborders. Characteristics Phacopida had 8 to 19 thoraci ...

. Species belonging to the Phacopina lived from the Lower

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

(

Tremadocian The Tremadocian is the lowest stage of Ordovician. Together with the later Floian Stage it forms the Lower Ordovician Epoch. The Tremadocian lasted from to million years ago. The base of the Tremadocian is defined as the First appearance datum ...

) through the end of the Upper

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

(

Famennian The Famennian is the later of two faunal stages in the Late Devonian epoch. The most recent estimate for its duration is that it lasted from around 371.1 to 359.3 million years ago. An earlier 2012 estimate, still used by the International Commis ...

).Moore, R.C. (ed.). Treatise on Invertebrate Paleontology. Part O – Arthropoda (Trilobitomorpha). 1959 The one unique feature that distinguishes Phacopina from all other trilobites are the very large, separately set lenses without a common cornea of the compound eye.

Habitat

As far as currently known, all Phacopina species were marine bottom-dwellers.

Origin

The Early Ordovician genus '' Gyrometopus'' (superfamily Dalmanitoidea, family Diaphanometopidae) is probably close to the common ancestor of the Phacopina. ''Gyrometopus'' is phacopid in appearance, but a rostral plate is present, unlike in other Phacopina. However, the rostral plate does not divide the cephalic doublure into a left and right section, but instead the rostral suture defines a semicircle in the frontal ¾ of the doublure.

Description

The eyes (if present) consist of very large (0.07mm in ''Tricopelta breviceps'' to 0.5mm in '' Phacops rana''), separately set lenses without a common cornea (so called schizochroal eyes). However, some Phacopina species lack eyes, such as the species of the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

'' Ductina''. The natural fracture lines (sutures) of the head run along the top edges of the compound eye. From the back of the eye these cut to the side of the head (proparian) and not to the back. In front of the eye, the right and left facial sutures connect in front of the inflated glabella and consequently the free cheeks (or librigenae) are yoked as a single piece. The part of the skeleton that is ‘tucked under’ (the doublure) has no sutures crossing it to form a rostral plate.
The thorax has 11 (rarely 10) segments, the side lobes (or pleurae) are furrowed, and the articulating facets distinct.Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997

Systematics

The Phacopina contain 3 superfamilies and 7 families: Superfamily Acastoidea *Family

Acastidae Acastidae is a family of trilobites in the order Phacopida, suborder Phacopina, superfamily Acastoidea, containing the following genera: References

Acastidae, Acastoidea Trilobite families {{Phacopida-stub ...

(examples: ''Coltraneia oufatenensis'', ''Walliserops trifurcatus'') *Family

Calmoniidae Calmoniidae is a family of trilobites from the order Phacopida Phacopida ("lens-face") is an order of trilobites that lived from the Late Cambrian to the Late Devonian. It is made up of a morphologically diverse assemblage of taxa in three rel ...

Superfamily

Dalmanitoidea Dalmanitoidea is a superfamily of trilobites in the order Phacopida, containing the three families Dalmanitidae Dalmanitidae is a family of trilobites in the order Phacopida that lived from the Floian (Ordovician) to the Devonian and includes ...

*Family

Dalmanitidae Dalmanitidae is a family of trilobites in the order Phacopida that lived from the Floian (Ordovician) to the Devonian and includes 33 genera. References

Dalmanitidae, Dalmanitoidea Trilobite families Early Ordovician first appearances ...

(examples: ''Dalmanites limulurus'', ''Huntoniatonia oklahomae'') *Family Diaphanometopidae *Family Prosopiscidae Superfamily Phacopoidea *Family

Phacopidae Phacopidae is a family (biology), family of Phacopida, phacopid trilobites that ranges from the Lower Ordovician to the Upper Devonian, with representatives in all Supercontinents, paleocontinents. Description As in all Phacopina, the eyes (if ...

(examples: '' Phacops rana'', ''Ductina vietnamica'') *Family Pterygometopidae

References

External links

fossilmuseum.net
- various photos, some of Phacopina {{Taxonbar, from=Q3821235 Phacopida Prehistoric animal suborders Arthropod suborders Early Ordovician first appearances Famennian extinctions