geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...

, the Arenig (or Arenigian) is a time interval during the

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 ...

period and also the suite of rocks which were deposited during this interval.

History

The term was first used by

Adam Sedgwick Adam Sedgwick (; 22 March 1785 – 27 January 1873) was a British geologist and Anglican priest, one of the founders of modern geology. He proposed the Cambrian and Devonian period of the geological timescale. Based on work which he did on W ...

in 1847 with reference to the "Arenig Ashes and Porphyries" in the neighbourhood of

Arenig Fawr Arenig Fawr ( en, Great High Ground) is a mountain in Snowdonia, North Wales, close to Llyn Celyn reservoir, alongside the A4212 between Trawsfynydd and Bala. Location Arenig Fawr is the highest member of the Arenig range, with Arenig Fach ( ...

, in

Merioneth , HQ= Dolgellau , Government= Merionethshire County Council (1889-1974) , Origin= , Status= , Start= 1284 , End= , Code= MER , CodeName= ...

North Wales , area_land_km2 = 6,172 , postal_code_type = Postcode , postal_code = LL, CH, SY , image_map1 = Wales North Wales locator map.svg , map_caption1 = Six principal areas of Wales common ...

. The rock-succession in the Arenig district has been recognized by W. G. Fearnsides (“On the Geology of Arenig Fawr and Moel Llanfnant", Q.J.G.S. vol. lxi., 1905, pp. 608–640, with maps). The above succession is divisible into: # A lower series of gritty and calcareous sediments, the "Arenig Series" as it is now understood; # A middle series, mainly volcanic, with shale, the "

Llandeilo Llandeilo () is a town and community in Carmarthenshire, Wales, situated at the crossing of the River Towy by the A483 on a 19th-century stone bridge. Its population was 1,795 at the 2011 Census. It is adjacent to the westernmost point of the B ...

Series"; and # The shale and limestones of the

Bala Bala may refer to: Places India *Bala, India, a village in Allahabad, India * Bala, Ahor, a village in the Jalore district of Rajasthan * Bala, Raebareli, a village in Uttar Pradesh, India Romania * Bala, Mehedinți, a commune in Mehedinţi ...

Caradoc Caradoc Vreichvras (; Modern cy, Caradog Freichfras, ) was a semi-legendary ancestor to the kings of Gwent. He may have lived during the 5th or 6th century. He is remembered in the Matter of Britain as a Knight of the Round Table, under the na ...

Stage. It was to the middle series (2) that Sedgwick first applied the term "Arenig". In the typical region and in North Wales generally the Arenig series appears to be unconformable upon the

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

rocks; this is not the case in South Wales. The Arenig series is represented in North Wales by the Garth Grit and

Ty Obry Ty (stylized as ty) is an American multinational corporation headquartered in Oak Brook, Illinois, a suburb of Chicago. It was founded by Ty Warner in 1986. It designs, develops and sells products, most notably Beanie Babies, exclusively to speci ...

beds, by the Shelve series of the Corndon district, the Skiddaw Slates of the Lake District, the

Ballantrae Group Ballantrae is a community in Carrick, South Ayrshire, Scotland. The name probably comes from the Scottish Gaelic ''Baile na Tràgha'', meaning the "town by the beach". Ballantrae has a primary school. The beach consists of shingle and sand an ...

Ayrshire Ayrshire ( gd, Siorrachd Inbhir Àir, ) is a historic county and registration county in south-west Scotland, located on the shores of the Firth of Clyde. Its principal towns include Ayr, Kilmarnock and Irvine and it borders the counties of Re ...

, and by the

Ribband Series A ribbon or riband is a thin band of material, typically cloth but also plastic or sometimes metal, used primarily as decorative binding and tying. Cloth ribbons are made of natural materials such as silk, cotton, and jute and of synthetic mater ...

of slates and shale in

Wicklow Wicklow ( ; ga, Cill Mhantáin , meaning 'church of the toothless one'; non, Víkingaló) is the county town of County Wicklow in Ireland. It is located south of Dublin on the east coast of the island. According to the 2016 census, it has ...

and

Wexford Wexford () is the county town of County Wexford, Ireland. Wexford lies on the south side of Wexford Harbour, the estuary of the River Slaney near the southeastern corner of the island of Ireland. The town is linked to Dublin by the M11/N11 N ...

. It may be mentioned here that the "

Llanvirn 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. The ...

" Series of H. Hicks was equivalent to the bifidus shale and the Lower Llandeilo Series.

Geochronology

In the

geologic timescale The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronol ...

, the Arenig or Arenigian refers to an age of the

Early 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. ...

epoch, between 477.7 and 470 million years ago, contemporary with 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 Dapingian Stage of the Middle Ordovician. The Floian extended from to million years ago. The lowe ...

of the ICS, based on a section in Sweden ( Diabasbrottet quarry) and with the same boundaries. The Arenig and Floian rocks are the upper part of the Lower Ordovician and follow the

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 ...

( Gasconadian in North America) which is the lower part. Either is followed by the Middle Ordovician ICS

Dapingian The Dapingian is the third stage of the Ordovician period and the first stage of the Middle Ordovician series. It is preceded by the Floian and succeeded by the Darriwilian. The top of the Floian is defined as the first appearance of the conodont s ...

or by the Llanvirnian of older chronologies. The Arenig and equivalent Floian are represented in North America by the upper three stages of the

Canadian Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...

which is followed by the

Middle 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. The ...

Whiterockian The Whiterockian, often referred to simply as the Whiterock, is an earliest or lowermost stage of the Middle Ordovician. Although the Whiterockian or Whiterock Stage refers mainly to the early Middle Ordovician in North America, it is often used in ...

which is the lower part of the now shortened

Chazyan The Chazy Reef Formation is a mid-Ordovician limestone deposit in northeastern North America. It consists of some of the oldest reef systems built by a community of organisms rather than the deposit of a limited range of similar organisms, such ...

Events

The Arenig rocks were deposited during a sudden worldwide rise in sea level resulting in widespread

marine transgression A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...

. The early Ordovician surge in marine diversity also began around this time.

Brachiopod fauna

;''

Incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, w ...

s of the Floian *''Eurorthisina'' *''Tegulella'' ; Acrotretida of the Floian *''Acanthambonia'' *'' Cyrbasiotreta'' *''Eoconulus'' *''Issedonia'' *'' Karnotreta'' *'' Lurgiticoma'' *'' Multispinula'' *'' Mylloconotreta'' *''Numericoma'' *''Orthisocrania'' *''Polylasma'' *'' Pomeraniotreta'' *''Pseudocrania'' *'' Scaphelasma'' *''Schizotreta'' *''Torynelasma'' ;

Lingulida Lingulida is an order of brachiopods. Extinct species The following are extinct species and genera belonging to the family Lingulidae.Emig C. C., Bitner M. A. & Álvarez F., 2019Linguliformea Brachiopoda database. Accessed 2020-09-27. *'' Lin ...

of the Floian *''Acanthorthis'' *''Aulonotreta'' *''Dictyobolus'' *''Ectenoglossa'' *'' Elliptoglossa'' *'' Monobolina'' *''Paldiskites'' *'' Paterula'' *'' Pseudolingula'' *'' Quasithambonia'' *'' Rafanoglossa'' *''Volborthia'' ;

Orthida Orthida is an extinct order of brachiopods which appeared during the Early Cambrian period and became very diverse by the Ordovician, living in shallow-shelf seas. Orthids are the oldest member of the subphylum Rhynchonelliformea, and is the ord ...

of the Floian *'' Acanthorthis'' *'' Acanthotoechia'' *'' Anchigonites'' *'' Angusticardinia'' *'' Anomalorthis'' *'' Antigonambonites'' *'' Apomatella'' *'' Astraborthis'' *'' Crossiskenidium'' *''Dalmanella'' *'' Desmorthis'' *''Diparelasma'' *'' Eodiorthelasma'' *''Eosotrematorthis'' *'' Estlandia'' *'' Euorthisina'' *'' Famatinorthis'' *'' Fasciculina'' *'' Ferrax'' *'' Ffynnonia'' *'' Fistulogonites'' *'' Glossorthis'' *''Glypterina'' *'' Hesperonomiella'' *'' Incorthis'' *'' Jaanussonites'' *'' Ladogiella'' *''Lomatorthis'' *'' Monorthis'' *'' Munhella'' *'' Nereidella'' *'' Neumania'' *'' Nocturneilla'' *'' Notoscaphidia'' *'' Oligorthis'' *'' Orthambonites'' *'' Orthidiella'' *'' Orthidium'' *'' Orthis'' *'' Oslogonites'' *'' Panderina'' *'' Paralenorthis'' *'' Paurorthina'' *'' Paurorthis'' *'' Phragmorthis'' *'' Platystrophia'' *'' Platytoechia'' *'' Polytoechia'' *'' Pomatotrema'' *'' Prantlina'' *'' Productorthis'' *'' Progonambonites'' *'' Protohesperonomia'' *'' Protoskenidiodes'' *'' Pseudomimella'' *'' Raunites'' *'' Rhynchorthis'' *'' Shoshonorthis'' *'' Sinorthis'' *'' Taphrorthis'' *''

Tarfaya Tarfaya ( ar, طرفاية - ''Ṭarfāya''; ber, ⵟⵔⴼⴰⵢⴰ) is a coastal Moroccan town, located at the level of Cape Juby, in western Morocco, on the Atlantic coast. It is located about 890 km southwest of the capital Rabat, and ...

'' *'' Treioria'' *'' Trematorthis'' *'' Valcourea'' *'' Virgoria'' ; Paternida of the Floian *'' Dictyonites'' ;

Pentamerida Pentamerida is an order of biconvex, impunctate shelled, articulate brachiopods that are found in marine sedimentary rocks that range from the Middle Cambrian through the Devonian.Moore, Lalcker and Fischer, 1952, Invertebrate Fossils, McGraw-Hil ...

of the Floian *'' Acanthorthis'' *'' Acanthoglypha'' *'' Boreadocamara'' *'' Camerella'' *'' Doloresella'' *'' Hesperotrophia'' *'' Idiostrophia'' *'' Imbricatia'' *'' Karakulina'' *'' Liricamera'' *'' Lycophoria'' *'' Porambonites'' *'' Rectotrophia'' *''

Rosella Rosellas are in a genus that consists of six species and nineteen subspecies. These colourful parrots from Australia are in the genus ''Platycercus''. ''Platycercus'' means "broad-tailed" or "flat-tailed", reflecting a feature common to the ...

'' *'' Rugostrophia'' *'' Stenocamara'' *''

Syntrophia The Syntrophales are an order of Thermodesulfobacteriota The Thermodesulfobacteriota are a phylum of thermophilic sulfate-reducing bacteria. A pathogenic intracellular thermodesulfobacteriote has recently been identified. Phylogeny The phyl ...

'' *'' Syntrophinella'' *'' Xenelasma''

Strophomenida

;

Strophomenida Strophomenida is an extinct order of articulate brachiopods which lived from the lower Ordovician period to the mid Carboniferous period. Strophomenida is part of the extinct class Strophomenata, and was the largest known order of brachiopods, ...

of the Floian *'' Acanthorthis'' *'' Ahtiella'' *'' Aporthophyla'' *'' Borua'' *'' Calyptolepta'' *'' Christiania'' *''

Ingria Ingria is a historical region in what is now northwestern European Russia. It lies along the southeastern shore of the Gulf of Finland, bordered by Lake Ladoga on the Karelian Isthmus in the north and by the River Narva on the border with Est ...

'' *'' Leptestia'' *'' Petroria'' *'' Plectambonites'' *'' Reinversella'' *'' Schedophyla'' *''Taffia'' *'' Tourmakeadia'' ;

Trimerellida Trimerellida is an extinct order of craniate brachiopods, containing the superfamily Trimerelloidea and the families Adensuidae, Trimerellidae, and Ussuniidae. Trimerellidae is a small but widespread family of warm-water brachiopods ranging f ...

of the Floian *'' Dinobolus''

Cephalopoda

;

Actinocerida The Actinocerida are an order of generally straight, medium to large cephalopods that lived during the early and middle Paleozoic, distinguished by a siphuncle composed of expanded segments that extend into the adjacent chambers, in which deposit ...

*'' Metactinoceras'' *'' Ordosoceras'' *'' Polydesmia''

Upper

The following is a list of Actinocerid genera whose fossils are geochronologically found first in ''upper Arenig strata''. These genera may survive into later portions of the Arenig stage, or even into later geological stages. This list should not be thought of in terms of the lifespan of the genera included. *''

Leurorthoceras ''Leurorthoceras'' is a genus of flattened actinoceratids with a siphuncle narrower than in ''Actinoceras ''Actinoceras'' is the principal and root genus of the Actinoceratidae, a major family in the Actinocerida, that lived during the Middl ...

'' *''

Nybyoceras ''Nybyoceras'' is an actinocerid genus assigned to the Armenoceratidae and similar to ''Armenoceras'' except for having a siphuncle close to the ventral side of the shell. Morphology As with ''Armenoceras'', ''Nybyoceras'' has a medium to large ...

'' *''

Actinoceras ''Actinoceras'' is the principal and root genus of the Actinoceratidae, a major family in the Actinocerida, that lived during the Middle and Late Ordovician. It is an extinct genus of nautiloid cephalopod that thrived in the warm waters of the U ...

'' *''

Wutinoceras ''Wutinoceras'' is a genus of now extinct nautiloid cephalopods of the Wutinoceratidae family. It exhibits orthoconic actinocerids with ventral siphuncles composed of broadly expanded segments.Memoir 2, Studies of the Actinocerida, New Mexic ...

'' *''

Ormoceras ''Ormoceras'' is an actinocerid nautiloid genus and type for the family Ormoceratidae, found in North America from the late Chazyan through the early Cincinnatian of the Middle and Upper Ordovician, but which continued through the Devonian worl ...

'' *''

Adamsoceras ''Adamsoceras'' is a genus of actinocerids of the family Wutinoceratidae, with spheroidal siphuncle segments like '' Ormoceras'', but having a reticular canal system like ''Wutinoceras''. Adamsoceras has a slender, gently expanding, orthoconic s ...

'' *''Georgina''

Orthocerida

; Orthocerids of the Floian *'' Eobactrites'' ; Barrandeocerida of the Floian *'' Plectoceras'' ;

Ellesmerocerida The Ellesmerocerida is an order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician. Morphology The Ellesmerocerida are characterized by shells that ...

of the Floian *'' Amsleroceras'' *'' Apocrinoceras'' *'' Avoceras'' *'' Bakeroceras'' *'' Baltoceras'' *'' Catoraphinoceras'' *'' Cochlioceras'' *'' Copiceras'' *'' Clelandoceras'' *'' Cumberloceras'' *'' Cyclostomiceras'' *'' Cyrtobaltoceras'' *'' Desioceras'' *'' Diaphoroceras'' *'' Diastoloceras'' *'' Dwightoceras'' *'' Dyscritoceras'' *'' Ectocycloceras'' *'' Endorioceras'' *'' Eocyckistomiceras'' *'' Eothinoceras'' *''

Hemichoanella The Genus ''Hemichoanella'' is a small, extinct, orthoconic nautiloid cephalopod from the Lower Ordovician of Western Australia assigned to the orthoceratoid family, ''Baltoceratidae''. ''Hemichoanella'' and the Baltoceratidae are part of the ...

'' *'' Irianoceras'' *'' Kyminoceras'' *'' Lawrenceoceras'' *'' Meikeloceras'' *'' Microbaltoceras'' *'' Monogonoceras'' *'' Ogygoceras'' *'' Pictetoceras'' *'' Protocycloceras'' *'' Quebecoceras'' *'' Rangeroceras'' *'' Rhabdiferous'' *'' Rioceras'' *'' Rudolfoceras'' *'' Smithvilloceras'' *''

Somalinautilus ''Somalinautilus'' is a genus of nautiloids that is found in the Middle to Upper Jurassic of England, France, and Somaliland. The genus contains three species, ''S. antiquus'', first assigned to ''Nautilus'' by Dacque in 1910, ''S. fuscus'', first ...

'' *''

'' *'' Vassaroceras'' *'' Veneficoceras'' *'' Ventroloboceras'' ;

Endocerida Endocerida is an extinct nautiloid order, a group of cephalopods from the Lower Paleozoic with cone-like deposits in their siphuncle. Endocerida was a diverse group of cephalopods that lived from the Early Ordovician possibly to the Late Silu ...

*''

Campendoceras ''Campendoceras'' is a genus of proterocameroceratids from the Lower Ordovician of NW Australia and possibly Estonia that can be recognized by its slender, weakly endogastric, longiconic and annulate shell and large marginal siphuncle that con ...

'' *'' Dartonoceras'' *'' Kaipingoceras'' *'' Kugeloceras'' *'' Lobosiphon'' *'' Manitouoceras'' *''

Mcqueenoceras ''Mcqueenoceras'' is an extinct genus of early endocerid, a nautiloid from the Floian epoch of the late early Ordovician period. It was similar in overall form to '' Clitendoceras'', from which it may have been derived. ''Mcqueenoceras'', like '' ...

'' *'' Mysticoceras'' *'' Notocycloceras'' *'' Oderoceras'' *'' Parapiloceras'' *'' Phragmosiphon'' *'' Platysiphon'' *'' Pliendoceras'' *'' Retroclitendoceras'' *'' Stenosiphon'' *'' Subpenhsioceras'' *'' Utoceras'' *'' Yorkoceras'' *'' Vaginoceras'' *'' Chisiloceras'' *'' Cyrtovaginoceras'' *'' Tallinnoceras'' *'' Juaboceras'' *'' Penhsioceras'' *'' Ventrolobendoceras'' ;Lower The following is a list of Endocerid genera whose fossils are geochronologically found first in ''lower Arenig strata''. These genera may survive into later portions of the Arenig stage, or even into later geological stages. This list should not be thought of in terms of the lifespan of the genera included. *'' Allopiloceras'' *'' Choreanoceroides'' *'' Escharendoceras'' *'' Lebetoceras'' *'' Loxochoanella'' *'' Sewardoceras'' *'' Telleroceras'' *''

Clitendoceras ''Clitendoceras'' is a genus of cephalopods in the order Endocerida from the Lower Ordovician (m-u Canadian) with an elongate shell with a slight downward, endogastric, curvature and a siphuncle that lies along the ventral margin. Common for end ...

'' *'' Coreanoceras'' *''

Cotteroceras ''Cotteroceras'' is a genus of proterocameroceratids from the Lower Ordovician of North America and Siberia characterized by a long straight and compressed shell with very short camerae and long body chamber. Sutures are straight and oblique, s ...

'' *'' Piloceras'' *''

Endoceras ''Endoceras'' (Ancient Greek for "inner horn") is an extinct genus of large, straight shelled cephalopods from the Middle and Upper Ordovician that gives its name to the Nautiloid order Endocerida. The cross section in the mature portion is slig ...

'' *''

Proterovaginoceras ''Proterovaginoceras'' (Ancient Greek for "earlier shield horn") is a medium to large sized endocerid (endocone-bearing orthoconic nautiliod) from the Early and Middle Ordovician included in the family Endoceratidae Endoceratidae is a family ...

'' *'' Cyrtendoceras'' *''

Anthoceras ''Anthoceras'' is a genus of straight, annulated, proterocamerioceratids (Order Endocerida) 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 ...

'' *'' Chaohuceras'' *''

Proterocameroceras ''Proterocameroceras'' is an early Endocerid from the upper Lower Ordovician belong to the Proterocameroceratidae The ''Proterocameroceratidae'' were the first of the Endocerida. They began early in the Ordovician with ''Proendoceras'' or simi ...

'' *'' Thylacoceras'' ;Upper The following is a list of Endocerid genera whose fossils are geochronologically found first in ''upper Arenig strata''. These genera may survive into later portions of the Arenig stage, or even into later geological stages. This list should not be thought of in terms of the lifespan of the genera included. *''

Allocotoceras ''Allocotoceras'' is an endocerid from the Lower Ordovician (upper Canadian) Karmberg Formation of Australia (Tasmania),Cassinoceras'' *'' Chihlioceras'' *'' Cyclocyrtendoceras'' *'' Cyptendoceras'' *'' Kirkoceras'' *''

Lobendoceras ''Lobendoceras'' is a proterocameraceratid with a rather large, moderately expanded, straight shell with a large marginal siphuncle in which sutures have a broad, deep, ventral lobe and septal necks are subholochoanitic to holochoanitic. Lobe ...

'' *''

Najaceras ''Najaceras'' is a genus of straight, slender endocerid known only from the Whiterockian age Oil Creek Limestone of Oklahoma, introduced and named by Rousseau Flower in 1971 and further described by him in 1976. ''Najaceras'' is characterized ...

'' *'' Protocyclendoceras'' *'' Yehlioceras'' *''

Nanno Nanno (german: Nain, Ladin: ''Nan'') was a ''comune'' (municipality) in Trentino in the northern Italian region Trentino-Alto Adige/Südtirol, located about north of Trento. As of 31 December 2004, it had a population of 623 and an area of .All ...

'' *'' Dideroceras'' *'' Lobocyclendoceras'' *''

Meniscoceras ''Meniscoceras'' is a straight and slender Chazyan endocerid described by Rousseau Flower in 1941 The genus was originally included in the Proterocameroceratidae (Flower, 1955) but later (Flower, 1976) placed with its predecessor, ''Najaceras'', ...

'' *'' Paracyclendoceras'' *'' Cacheoceras'' *''

Perkinsoceras ''Perkinsoceras''is an endocerid genus from the Middle Ordovician (Chazyan) of Champlain Valley established by Flower in 1976, which he added to his Allotrioceratidae based on certain similarities to ''Williamsoceras'' and '' Cacheoceras'' which ...

'' *''

Williamsoceras Williamsoceras is an endocerid that Rousseau Flower (1968) added to his Allotrioceratidae (Flower 1955) on the basis of having a vertical partition within the siphuncle, known as a ventral process, with inter-connecting tubule-like structure ...

'' *'' Manchuroceras'' *'' Schmidtoceras'' ;

Intejocerida Intejocerida is the name given to a group of generally straight shelled nautiloid cephalopods originally found in Lower and Middle Ordovician sediments in the Angara River basin in Russia; defined in the Treatise as an order, and combined there w ...

of the Floian *''

Bajkaloceras ''Bajkaloceras'' is a straight-shelled orthoceroid, and possibly a member of the Intejocerida, from the Angara River basin in central Russia, named by Balashov in 1962. Its age, as given in the Treatise on Invertebrate Paleontology is Arenigian ...

'' *'' Evencoceras'' *'' Intejoceras'' *'' Rossoceras'' ; Oncocerids of the Floian *'' Phthanoncoceras'' *'' Valhalloceras'' ;

Nautiloids Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species. ...

of the Floian *'' Buttsoceras'' *'' Centroonoceras'' *'' Gangshanoceras'' *'' Geisonoceras'' *'' Glenisteroceras'' *''

Michelinoceras ''Michelinoceras'' is the oldest known genus of the Michelinocerida, more commonly known as the Orthocerida, characterized by long, slender, nearly cylindrical orthocones with a circular cross section, long camerae, very long body chambers, and a ...

'' *''

Orthoceras ''Orthoceras'' ("straight horn") is a genus of extinct nautiloid cephalopod restricted to Middle Ordovician-aged marine limestones of the Baltic States and Sweden. This genus is sometimes called ''Orthoceratites''. Note it is sometimes misspelle ...

'' *'' Oxfordoceras'' *''

Rhynchorthoceras ''Rhynchorthoceras'' is a Middle Ordovician genus characterized by a rapidly expanded, weakly annulate orthocone, like the orthoconic section of ''Ancistroceras'', but with only a curved, cyrtoconic apex instead of juvenile whorls. ''Rhynchorth ...

'' *'' Stereoplasmoceras'' *'' Tajaroceras'' *'' Wardoceras'' ;

Tarphycerida The Tarphycerida were the first of the coiled cephalopods, found in marine sediments from the Lower Ordovician (middle and upper Canad) to the Middle Devonian. Some, such as '' Aphetoceras'' and '' Estonioceras'', are loosely coiled and gyroconi ...

*'' Deltoceras'' *'' Pseudancistroceras'' *'' Seelyoceras'' ;Lower *''

Alaskoceras ''Alaskoceras'' is a genus of lower Ordovician coiled nautiloid cephalopods; the shell moderately expanded, ribbed, with a divergent living chamber; whorl section more broadly rounded ventrally than dorsally; siphuncle marginal at maturity, septa ...

'' *'' Moreauoceras'' *'' Pilotoceras'' *'' Shumardoceras'' *'' Pycnoceras'' *''

Campbelloceras ''Campbelloceras'' is a tarphyceratid nautiloid known from the Lower Ordovician, Upper Canadian Epoch of North America, where it is widespread. ''Campbelloceras'' was named by Ulrich and Foerste in 1936. The shell of ''Campbelloceras'' has a ci ...

'' *''

Aphetoceras ''Aphetoceras'' is a genus of tarphycerid cephalopod within the Estonioceratidae; loosely coiled without an impression along the dorsal margin; early whorls barely reaching, separating then diverging in the final mature whorl; weakly ribbed in s ...

'' ;Upper *'' Aethoceras'' *'' Bentoceras'' *'' Centrotarphyceras'' *'' Clytoceras'' *'' Cycloplectoceras'' *'' Eichwaldoceras'' *'' Eurystomites'' *''

Hardmanoceras ''Hardmanoceras'' is a tarphycerid genus belonging to the Trocholitidae from the upper Lower Ordovician to possibly the lower Middle Ordovician, found in Western Australia. ''Hardmanoceras'' is like ''Discoceras ''Discoceras'' is an extinct m ...

'' *''

Holmiceras ''Holmiceras'' is one of two ancestral lituitids from the late Early Ordovician (Arenigian). The other being ''Ancistroceras''. ''Holmiceras'' begins with about 1.5 to 2 loosely coiled whorls followed by a rapidly expanding orthocone, much like ...

'' *'' Pionoceras'' *'' Trocholitoceras'' *'' Wichitoceras'' *''

Tarphyceras ''Tarphyeras'' is a genus of tarphyceratid with whorls rounded in cross section, having a deeply impressed dorsum and a ventral to subcentral siphuncle, known from the Lower Ord (U Canad) of North America. It differs from '' Campbelloceras'' in ...

'' *''

Litoceras ''Litoceras'' is a trocholitid (Tarphycerida) genus that has been found in the Lower and Middle Ordovician of Newfoundland. Whorls in ''Litoceras'' have a broadly rounded cross section with its width greater than its height. Litoceras somewhat ...

'' *''

Curtoceras ''Curtoceras'' is a genus in the tarphycerid family Trocholitidae found widespread in the late Early and Middle Ordovician of North America and northern Europe. ''Curtoceras'' has a shell that is gradually expanded, with half the fully mature bo ...

'' *'' Arkoceras'' *'' Estonioceras'' *'' Tragoceras''

Trilobite fauna

;Trilobites of the Floian *'' Canningella'' *'' Gogoella'' *''

Macrogrammus ''Macrogrammus'' is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the early part of the Arenig, Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 478 to 4 ...

'' *'' Priceaspis'' *'' Thymurus'' ;

Agnostida Agnostida is an order of arthropod which have classically been seen as a group of highly modified trilobites, though some recent research has doubted this placement. Regardless, they appear to be close relatives as part of the Artiopoda. They a ...

of the Floian' *'' Galbagnostus'' *'' Geragnostella'' ;

Asaphida Asaphida is a large, morphologically diverse order of trilobites found in marine strata dated from the Middle Cambrian until their extinction during the Silurian. Asaphida contains six superfamilies (Anomocaroidea, Asaphoidea, Cyclopygoidea, ...

of the Floian Naturhistorisches Museum Vienna Dez 2006 073

*'' Phthanoncoceras'' *''

Ampyx In Greek mythology, Ampyx (Ancient Greek: Ἄμπυξ) or Ampycus (Ἄμπυκος ''Ampykos'' means 'woman's diadem, frontlet') was the name of the following figures: * Ampyx, also called Ampycus or AmpyceHesiod, ''Shield of Heracles'' 180 was a ...

'' *'' Ampyxoides'' *'' Anebolithus'' *''

Asaphus ''Asaphus'' () is a genus of trilobites that is known from the Lower (upper Arenig) and Middle Ordovician of northwestern Europe (Sweden, Estonia, Saint Petersburg Area). Etymology The generic name is derived from the Greek word ''asaphes'', ...

'' *''

Aspidaeglina ''Aspidaeglina'' is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the early part of the Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 473 to 470 mill ...

'' *''

Australopyge ''Australopyge'' 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 The Ordovician ( ) is a geologic period and system, the second of six periods o ...

'' *'' Bergamia'' *'' Bohemopyge'' *''

Borogothus ''Borogothus'' is an extinct genus of trilobite arthropod. It lived during the Arenig stage of the Ordovician Period The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 ...

'' *'' Bumastides'' *''

Ceratolithus ''Ceratolithus'' is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the later part of the Arenig, Arenig stage of the Ordovician Period, approximately 478 to 471 million years ago. Distribut ...

'' *''

Cloacaspis ''Cloacaspis'' is an extinct genus of Olenid Ptychopariid trilobite. It lived during the early part of the Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 478 to 471 million years ago. Richard Fortey ...

'' *''

Cnemidopyge ''Cnemidopyge'' is a genus of trilobites that lived during the Ordovician. Like all Raphiophorids it is blind, with a cephalon that is subtriangular to subsemicircular, carrying genal spines and a forward directed rapier-like spine on the central ...

'' *'' Degamella'' *'' Dionide'' *'' Dionidella'' *'' Ellipsotaphrus'' *'' Falanapis'' *'' Famatinolithus'' *''

Globampyx ''Globampyx'' is an extinct genus raphiophorid trilobites. It lived during the later part of the Arenig stage of the Ordovician Period, approximately 478 to 471 million years ago. Species of the genus are known from Canada (southeastern British ...

'' *'' Gog'' *'' Hanchungolithus'' *'' Hoekaspis'' *'' Hungioides'' *''

Hunnebergia ''Hunnebergia'' is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the early part of the Arenig, Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 478 to 47 ...

'' *'' Isocolus'' *'' Isoteloides'' *''

Lachnostoma ''Lachnostoma'' is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the early part of the Arenig stage of the Ordovician Period, a faunal stage In chronostratigraphy, a stage is a successio ...

'' *''

Lannacus ''Lannacus'' 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 The Ordovician ( ) is a geologic period and system, the second of six periods of th ...

'' *'' Lapidaria'' *'' Liomegalaspides'' *'' Megalaspidella'' *'' Megalaspides'' *''

Mendolaspis ''Mendolaspis'' is an extinct genus of trilobites. It lived during the Arenig stage of the Ordovician Period The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million ...

'' *'' Merlinia'' *'' Microparia'' *'' Mioptychopyge'' *'' Myttonia'' *'' Ningkianolithus'' *'' Niobides'' *'' Ogmasaphus'' *'' Ogyginus'' *'' Ogygiocaris'' *'' Opipeuter'' *'' Parabasilicus'' *'' Paraptychopyge'' *'' Plesiomegalaspis'' *'' Presbynileus'' *''

Pricyclopyge ''Pricyclopyge'' is a genus of trilobites assigned to the family Cyclopygidae that occurs throughout the Ordovician. ''Pricyclopyge'' had aextratropical distribution, and there is evidence that it lived in darker parts of the water column (aroun ...

'' *'' Psilacella'' *'' Psilocara'' *'' Ptychopyge'' *'' Rhombampyx'' *'' Robergiella'' *'' Seleneceme'' *'' Stapeleyella'' *'' Taihungshania'' *'' Thysanopyge'' *'' Trigonocercella'' *'' Tungtzuella'' *'' Zhenganites'' *'' Zuninaspis'' ; Corynexichida of the Floian *''

Bumastus ''Bumastus'' is an extinct genus of corynexochid trilobites which existed from the Early Ordovician period to the Late Silurian period. They were relatively large trilobites, reaching a length of . They were distinctive for their highly globular ...

'' *'' Dysplanus'' *'' Ectillaenus'' *'' Panderia'' *'' Phillipsinella'' *'' Pseudocalymene'' *'' Theamataspis'' ;

Lichida Lichida is an order of typically spiny trilobite that lived from the Furongian to the Devonian period. These trilobites usually have 8–13 thoracic The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals l ...

of the Floian *''

Apatolichas ''Apatolichas'' is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the later part of the Arenig stage of the Ordovician Period The Ordovician ( ) is a geologic period and system, the second ...

'' *'' Autoloxolichas'' *'' Lichakephalina'' *'' Metopolichas'' ;

Odontopleurida Odontopleurida is an order (biology), order of very spinose trilobites closely related to the trilobites of the order Lichida. Some experts group the Odontopleurid families, Odontopleuridae and Damesellidae, within Lichida. Odontopleurids tend ...

of the Floian *'' Phthanoncoceras'' *'' Ceratocephala'' *'' Diacanthaspis'' *''

Selenopeltis ''Selenopeltis'' () is an extinct genus of odontopleurid trilobites in the family Odontopleuridae. Species in the genus ''Selenopeltis'' can reach a length of and a width of . These trilobites show long pleural spines and were a low-level ...

'' ;

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 ...

of the Floian *'' Bathycheilus'' *''

Calymenella ''Calymenella'' is a genus of trilobites in the order Phacopida, which existed in what is now France during the upper Ordovician. It was described by Bergeron in 1890, and the type species is ''Calymenella boisseli''. The species was described fr ...

'' *'' Ceraurinella'' *'' Colobinion'' *''

Colpocoryphe ''Colpocoryphe'' is a genus of trilobites in the family Calymenidae Calymenidae is a family of trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earlies ...

'' *'' Cybelopsis'' *'' Cybelurus'' *'' Diaphanometopus'' *'' Dindymene'' *'' Eccoptochile'' *'' Ectenonotus'' *'' Encrinurella'' *''

Encrinuroides ''Encrinuroides'' is a genus of trilobites in the order Phacopida, that existed during the upper Ordovician in what is now Wales. It was described by Reed in 1931, and the type species is ''Encrinuroides sexcostata'', which was originally descri ...

'' *'' Evropeites'' *''

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 ...

'' *'' Heliomeroides'' *'' Kanoshia'' *'' Kawina'' *'' Kolymella'' *''

Lehua Lehua Island is a small, crescent-shaped island in the Hawaiian islands, north of Niihau, due west of Kauai. The uninhabited, barren island is a tuff cone which is part of the active Niihau volcano. Lehua was one of the first five islands ...

'' *'' Lyrapyge'' *'' Neseuretus'' *'' Nieszkowskia'' *'' Ormathops'' *'' Ovalocephalus'' *'' Placoparia'' *'' Platycoryphe'' *'' Pliomeridius'' *'' Pliomerops'' *'' Protoencrinurella'' *'' Protopliomerella'' *'' Pseudocybele'' *'' Pterygometopus'' *'' Strotactinus'' *'' Sycophantia'' *'' Synhomalonotus'' *'' Toletanaspis'' *'' Xystocrania'' ;

Proetida Proetida is an order of trilobite that lived from the Ordovician to the Permian. It was the last order of trilobite to go extinct, finally dying out in the Permian-Triassic extinction event. Description These typically small trilobites resem ...

of the Floian *'' Acidiphorus'' *'' Bathyuriscops'' *'' Benthamaspis'' *'' Biolgina'' *''

Bolbocephalus ''Bolbocephalus'' is a genus of proetid trilobites in the family Bathyuridae. Species lived during the early part of the Arenig stage of the Ordovician Period, a faunal stage which lasted from approximately 478 to 471 million years ago, in mar ...

'' *''

Carolinites ''Carolinites'' is a genus of trilobite, assigned to the Telephinidae family, that occurs during the Lower and Middle Ordovician. ''Carolinites'' had a pantropical distribution, and there is evidence that it lived in upper parts of the water co ...

'' *''

Celmus ''Celmus'' is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the later part of the Arenig stage of the Ordovician Period The Ordovician ( ) is a geologic period and system, the second of si ...

'' *''

Ceratopeltis ''Ceratopeltis'' 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 The Ordovician ( ) is a geologic period and system, the second of six periods of ...

'' *'' Decoroproetus'' *'' Dimeropygiella'' *'' Eleutherocentrus'' *'' Goniophrys'' *'' Goniotelina'' *'' Grinnellaspis'' *'' Ischyrophyma'' *'' Ischyrotoma'' *'' Lutesvillia'' *'' Oenonella'' *'' Petigurus'' *''

Rananasus ''Rananasus'' is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the early part of the Arenig stage of the Ordovician Period, a faunal stage In chronostratigraphy, a stage is a succession ...

'' *'' Raymondaspis'' *'' Telephina'' ;

Ptychopariida Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. The earliest species occurred in the second half of the Lower Cambrian, and the last species did not survive the Ordovician–Silurian ...

of the Floian *''

Anaximander Anaximander (; grc-gre, Ἀναξίμανδρος ''Anaximandros''; ) was a pre-Socratic Greek philosopher who lived in Miletus,"Anaximander" in ''Chambers's Encyclopædia''. London: George Newnes, 1961, Vol. 1, p. 403. a city of Ionia (in moder ...

'' *'' Annamitella'' *''

Balnibarbi Balnibarbi is a fictional land in Jonathan Swift's 1726 satirical novel ''Gulliver's Travels''. it was visited by Lemuel Gulliver after he was rescued by the people of the flying island of Laputa. Location The location of Balnibarbi is illustra ...

'' *''

Bulnibarbi Balnibarbi is a fictional land in Jonathan Swift's 1726 satirical novel ''Gulliver's Travels''. it was visited by Lemuel Gulliver after he was rescued by the people of the flying island of Laputa. Location The location of Balnibarbi is illustra ...

'' *'' Bvalbardites'' *''

Circulocrania ''Circulocrania'' is an extinct genus of trilobites in the family Cyclopygidae. The genus lived during the later part of the Arenig stage of the Ordovician Period The Ordovician ( ) is a geologic period and system, the second of six periods ...

'' *'' Endymionia'' *''

Etheridgaspis ''Etheridgaspis'' 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 The Ordovician ( ) is a geologic period and system, the second of six periods ...

'' *'' Furcalithus'' *'' Gymnostomix'' *'' Lacorsalina'' *'' Leioshumardia'' *'' Lordshillia'' *'' Nambeetella'' *'' Novakella'' *'' Oopsites'' *'' Peraspis'' *'' Phorocephala'' *'' Porterfieldia'' *'' Prosopiscus'' *''

Pytine ''Pytine'' is an extinct genus of asaphida, asaphid trilobites. Species lived during the later part of the Arenig, Arenig stage of the Ordovician Period, approximately 478 to 471 million years ago. Various species are found in the Svalbard, Val ...

'' *''

Sagavia ''Sagavia'' is a genus of trilobites that lived during the Middle and Upper Ordovician in what are now Northwest and Southeast China, North Kazakhstan and Wales. It is a typical cyclopygid that can be distinguished by its large but separate eye ...

'' *'' Selenoharpes'' *'' Stegnopsis'' *'' Stenorhachis'' *'' Svalbardites'' *'' Tasmanocephalus'' *'' Turgicephalus'' *'' Yinpanolithus''

External links

palaeos

References

{{Reflist Early Ordovician