The Phacopina comprise a suborder of the

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

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 thorac ...

. 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. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

(

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 of the ...

) through the end of the Upper

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

(

Famennian The Famennian is the latter of two faunal stages in the Late Devonian Epoch. The most recent estimate for its duration estimates that it lasted from around 371.1 million years ago to 359.3 million years ago. An earlier 2012 estimate, still used b ...

).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 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 ''Eldredgeops rana'' (formerly ''Phacops rana'') is a species of trilobite from the middle Devonian period. Their fossils are found chiefly in the northeastern United States, and southwestern Ontario. Because of its abundance and popularity wit ...

''), 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 ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

Ductina ''Ductina'' is a genus of extinct, small to average sized, eyeless phacopid trilobite, that lived during the Devonian. Description The body of ''Ductina'' is small to average (up to ), 1¼ to 2 times as long as wide, blunted oval. Body wit ...

''. 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

Phacopoidea Phacopoidea is a superfamily of trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites ...

*Family

Phacopidae Phacopidae is a family of phacopid trilobites that ranges from the Lower Ordovician to the Upper Devonian, with representatives in all paleocontinents. Description As in all Phacopina, the eyes (if present) consist of very large (0.5 mm in ' ...

(examples: ''

'', ''Ductina vietnamica'') *Family Pterygometopidae Superfamily Dalmanitoidea *Family

Dalmanitidae Dalmanitidae is a family of trilobites in the order Phacopida that lived from the Floian The Floian is the second stage of the Ordovician Period. It succeeds the Tremadocian with which it forms the Lower Ordovician epoch. It precedes the Dap ...

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

Acastidae Acastidae is a family of trilobites in the order Phacopida, suborder Phacopina The Phacopina comprise a suborder of the trilobite order Phacopida. Species belonging to the Phacopina lived from the Lower Ordovician ( Tremadocian) through the end ...

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

Calmoniidae Calmoniidae is a family of trilobites from the order Phacopida, suborder Phacopina, superfamily Acastoidea. It contains the following genera: *'' Anchiopella'' *'' Andinacaste'' *'' Australocaste'' *'' Australops'' *'' Awaria'' *'' Bainella'' * ...

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