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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 ...
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 ...
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, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...
( Tremadocian) 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, wh ...
(
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 ...
).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 ''Gyrometopus'' is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the Arenig stage of the Ordovician Period, approximately 479 to 472 million years ago. Description The central raised ar ...
'' (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 living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
''
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 witho ...
''. 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 SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamil ...
*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: ''
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 ...
'', ''Ductina vietnamica'') *Family
Pterygometopidae The Pterygometopidae are a family of trilobites, that is known from the Floian to the Katian (Ordovician), and reappears from the Telychian to the Sheinwoodian (Silurian). As part of the Phacopina suborder, its members have schizochroal eyes. D ...
Superfamily Dalmanitoidea *Family Dalmanitidae (examples: ''Dalmanites limulurus'', ''Huntoniatonia oklahomae'') *Family Prosopiscidae *Family
Diaphanometopidae Diaphanometopidae is a family of trilobites. Its representatives lived during the Arenig and Llanvirn stages of the Ordovician Period, approximately 479 to 463 million years ago.Moore, R. C. (ed.). Treatise on Invertebrate Paleontology. Part O ...
Superfamily
Acastoidea Acastoidea is a superfamily of trilobites from the order Phacopida, suborder Phacopina. This superfamily is divided into two families, Acastidae and Calmoniidae. This superfamily is distinguishable from the Phacopidae in that eyes are closer t ...
*Family
Acastidae Acastidae is a family of trilobites in 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 related ...
(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