Trinodus

{{Short description|Extinct genus of trilobites}} {{Automatic taxobox | fossil_range = {{Geological range|488|445|Ordovician}} | image = Arthrorhachis tarda draw entite.png | image_alt = A drawing of "Trinodus tardus" | image_caption = A drawing of ''Trinodus tardus'' | taxon = Trinodus | authority = M'Coy, 1846 | synonyms = *{{extinct}}''Arthrorhachis'' *{{extinct}}''Girvanagnostus'' *{{extinct}}''Metagnostus'' | synonyms_ref = | type_species = {{extinct}}''Trinodus agnostiformes'' | type_species_authority = M'Coy, 1846 | subdivision_ranks = Species | subdivision = *{{extinct}}''Trinodus agnostiformes'' M'Coy, 1846 synonyms ''A. agnostiformis'', ''A. trinodus'' *{{extinct}}''Trinodus tardus'' (Barrande,1846) synonyms ''Battus tardus'', ''Agnostus glabratus'', ''A. tardus''<ref name="Budil">{{cite journal|last1= Budil|first1= P.|last2= Fatka|first2= O.|last3= Kolář|first3= P.|last4= David|first4= M.|year= 2011|title= ''Arthrorhachis'' Hawle & Corda, 1847 (Agnostida) in the Prague Basin revisited|journal= Bulletin of Geosciences|volume= 86|issue= 4|pages= 707–724|doi= 10.3140/bull.geosci.1262|url= http://www.geology.cz/bulletin/fulltext/1262_Budil.pdf|doi-access= free}}</ref> ''Arthrorhachis tarda'', alternative spelling ''A. tardus'' *{{extinct}}''Trinodus elspethi'' (Raymond, 1925) synonym ''Arthrorhachis elspethi'' *{{extinct}}''Trinodus danicus'' Poulsen, 1965 synonym ''Arthrorhachis danica'' *{{extinct}}''Trinodus girvanensis'' (Reed, 1903) synonyms ''Agnostus girvanensis'', ''Arthrorhachis girvanensis'', ''Girvanagnostus girvanensis'' *{{extinct}}''Trinodus hupehensis'' Lu, 1975 synonym ''Arthrorhachis hupehensis'' *{{extinct}}''Trinodus knockerkensis'' Romano & Owen, 1993 synonym ''Arthrorhachis knockerkensis'' *{{extinct}}''Trinodus latilimbata'' (Ju ''in'' Qiu ''et al.'', 1983)synonym ''Arthrorhachis latilimbata'' *{{extinct}}''Trinodus pragensis'' (Přibyl & Vaněk, 1968) synonym ''Arthrorhachis pragensis'' }}

'''''Trinodus''''' is a very small to small (about {{convert|1|cm|in|disp=or}}) blind trilobite, a well known group of extinct marine arthropods, which lived during the Ordovician (Tremadocian to early Hirnantian),<ref name="Budil"/> in what are now the Yukon Territories, Virginia, Italy, Czech Republic, Poland, Denmark, Sweden, Svalbard, Ireland, Scotland, Wales, Iran, Kazakhstan and China. It is one of the last of the Agnostida order to survive.

== Etymology == ''Trinodus'' is derived from the Latin tri (three) and nodus (node). ''Arthrorhachis'' is derived from the Greek ἄρθρον (''árthron'', "joint") and ῥάχις (''rháchis'', meaning axis, spine, ridge or backbone).<ref name="Budil"/>

== Taxonomy == ''Trinodus'', ''Arthrorhachis'' and ''Geragnostus'' are closely related and it may be appropriate to assign their species to just one genus. All species in these three genera have virtually identical cephalons, but of ''T. agnostiformes'', the type species of ''Trinodus'' only one poorly preserved cephalon was known. However, relatively recent, pygidia assignable to ''T. agnostiformes'' were found. Although this material is distorted or incompletely preserved, it is very similar to the pygidium of ''Arthrorhachis tarda''. Species with a rear rhachis lobe longer than the postaxial region are henceforth combined in ''Geragnostus'', all others are assigned to ''Trinodus''.<ref name='Turvey'>{{cite journal|last= Turvey|first= S.T.|year= 2005|title= Agnostid trilobites from the Arenig-Llanvirn of South China|journal= Transactions of the Royal Society of Edinburgh: Earth Sciences|volume= 95|issue= 3–4|pages= 527–542|doi=10.1017/s026359330000119x|s2cid= 130775617}}</ref>

=== Species previously assigned to ''Trinodus'' === * ''T. glabratus'' var. ''kirgizica'' = ''Geragnostus kirgizica'' * ''T. kirgizica'' = ''Geragnostus kirgizica'' * ''T. longicollis'' = ''Geragnostus longicollis''

== Distribution == * '''''T. agnostiformes''''' was identified in the Upper Ordovician of Ireland (Caradoc, Greenville slates, Campile Formation).<ref name='Karim'>{{cite journal|last= Karim|first=T.S.|year= 2009|title= Ordovician trilobites from Iran|journal= Earth and Environmental Science Transactions of the Royal Society of Edinburgh|volume= 99|issue= 2|pages= 101–124|doi=10.1017/s1755691009007063|s2cid=129780250 }}</ref> * '''''Trinodus danicus''''' occurs in Ordovician of Svalbard (Ibexian 488.3 - 471.8 Mya, ''Psephosthenaspis nasuta'' trilobite zone, Olenidsletta Member, Valhallfonna Formation, Ny Friesland, 79.8° N, 17.8° E).<ref>{{cite journal|last=Fortey|first= R. A.|authorlink = Richard Fortey|year=1980|title= The Ordovician trilobites of Spitsbergen. III. Remaining trilobites of the Valhallfonna Formation|journal= Norsk Polarinstitutt Skrifter|volume=171|pages=1–163|url= https://paleobiodb.org/classic/displayCollResults?collection_no=106473}}</ref> * '''''Trinodus elspethi''''' is present in the Upper Ordovician of the USA (Kathian?, Athens Shale, Ina railroad cutting, South of Otes, North of Bulls Gap, Hawkins, Tennessee).<ref name="Budil"/> * '''''T. hupehensis''''' has been found in the Middle Ordovician of China (Dawan Formation, upper Arenig, Fenxiang, Yichang County, West Hubei).<ref name='Turvey'/> * '''''Trinodus knockerkensis''''' has been collected from the Ordovician of Ireland (Lower Caradoc, Brickwork's Quarry Shales Member, Knockerk Formation, 53.8° N, 6.6° W).<ref>{{cite journal|last1= Romano|first1=M. |last2= Owen|first2= A. W.|year= 1993|title= Early Caradoc Trilobites of Eastern Ireland and their paleogeographical significance|journal= Palaeontology|volume=36|issue=3|pages=681–720|url= https://paleodb.org/cgi-bin/bridge.pl?a=displayCollResults&taxon_no=19186&max_interval=Ordovician&country=Ireland&is_real_user=1&basic=yes&type=view&match_subgenera=1}}</ref> * '''''Trinodus pragensis''''' is present in the Upper Ordovician of the Czech Republic (Lower Katian, abandoned brickyard “Na bílém koni”, Bohdalec Formation, Karlíkore Horizon, Praha-Hloubětín). ''A. pragensis'' precedes ''A. tardus'' in Czech Republic.<ref name="Budil"/> * '''''Trinodus tardus''''' is present in the Upper Ordovician of Denmark (Læså - stream section at Vasegård -, Øleå - stream section at Billegrav Gård -, and Risebæk, all Bornholm),<ref name='Ahlberg'>{{cite journal|last=Ahlberg|first=P.|year=1989|title=Agnostid trilobites from the Upper Ordovician of Sweden and Bornholm, Denmark|journal= Bulletin of the Geological Society of Denmark|volume= 37|pages= 213–226|doi=10.37570/bgsd-1988-37-17 |url= http://2dgf.dk/xpdf/bull37_03-04-213-226.pdf}}</ref> of Sweden (In Skåne: Koången in the classical Fågelsång area east of Lund; Koången core; Lindegård core; Rostånga; Tommarp; Jerrestad, stream section in the Jerrestadsån rivulet; Tosterup. In Östergötland: Råssnäs and Rödbergsudde, both near Motala. In Västergötland: Lower Jonstorp Formation "Green ''Tretaspis'' Shale" at Bestorp – Mosseberg. Upper Jonstorp Formation "Red ''Tretaspis'' Shale" and Ulunda Mudstone of the upper Jerrestadian Stage at Stommen (Kungslena); Varvsberget, Skogastorp, Plantaberget (Högstenaberget); Skultorp, Billingen; Rustsäter, Kinnekulle; Kullatorp core, Kinnekulle. In Dalarna: Vikarbyn and Gulleråsen-Sanden)<ref name='Ahlberg'/> of Norway (Oslo Region, Hovedøya, Spannslokket Member of the Skogerholmen Formation; Åslund, Hadeland Gagnum Shale Member of the Lunner Formation)<ref name='Ahlberg'/> of the Czech Republic (upper Katian, ''Tretaspis seticornis'' community, Kraluv Dvur Formation),<ref>{{cite book|last1= Chlupac|first1=I.|last2= Havlicek|first2= V.| last3=Kukal|first3=Z.|last4= Storch|first4=P.|year=1998|title= Palaeozoic of the Barrandian (Cambrian to Devonian)|pages=1–183|url= https://paleobiodb.org/classic/displayCollResults?collection_no=76478}}</ref> of Italy (''Foliomena'' community, Domusnovas Formation, Punta S'Argiola, Sardinia, 40.0° N, 8.0° E),<ref>{{cite journal|last1=Leone|first1= F.|last2= Hammann |first2=W.|last3= Laske|first3=R.|last4= Serpagli|first4= E.|last5= Villas|first5= E.|year= 1991|title=Lithostratigraphic units and biostratigraphy of the post-sardic Ordovician sequence in south-west Sardinia|journal= Bollettino della Societá Paleontologica Italiana|volume=30|pages=201–235|url= https://paleodb.org/cgi-bin/bridge.pl?a=displayCollResults&taxon_no=19186&max_interval=Ordovician&country=Italy&is_real_user=1&basic=yes&type=view&match_subgenera=1}}</ref> of Iran (late Caradoc, early Asgill, Tatavrud, 35 km southwest of Bandar-e-Anzali),<ref name='Karim' /> and of Kazakhstan.<ref name='Ahlberg'/> * '''''Trinodus sp.''''' (presumably ''T. tardus'') has been collected from the Ordovician of Czech Republic (Králův Dvůr Formation, Prague Basin).<ref>{{cite journal|last1= Havlicek|first1= V. |last2= Vanek|first2=J.|year= 1990|title= Ordovician Invertebrate communities in black-shale lithofacies (Prague Basin, Czechoslovakia)|journal= Vestnik Ustredniho Ustavu Geologickeho|volume=65|pages=223–236|url= https://paleobiodb.org/classic/displayCollResults?collection_no=3876}}</ref> * '''''Trinodus sps.''''' are found in the Ordovician of Canada (Llanvirn, Road River Formation, ''Peraspis'' fauna, Yukon Territory, 62.8° N, 136.6° W, and Cnemidopyge fauna, 65.0° N, 111.5° W),<ref>{{cite journal|last= Ludvigsen|first= R.|year= 1981|title= Biostratigraphical significance of Middle Ordovician trilobites from the Road River Formation, northern Cordillera|journal= Geological Association of Canada, Abstracts|volume=6|issue= A-36|url= https://paleobiodb.org/classic/displayCollResults?collection_no=302}}</ref> of China (Baota (Pagoda) Formation, NingLang, NingLang County, Yunnan),<ref>{{cite book|author=Stratigraphic Group of Yunnan, China|year=1978|title= Regional stratigraphic data of Southwest China, Yunnan Province|publisher= Geological Publishing House|location= Beijing|url=https://paleodb.org/cgi-bin/bridge.pl?a=displayCollResults&taxon_no=19186&max_interval=Ordovician&country=China&is_real_user=1&basic=yes&type=view&match_subgenera=1)}}</ref> of Poland (Hirnantian, Holycross Mountains, 51.0° N, 21.0° E),<ref>{{cite journal|last= Temple|first= J.T.|year=1965|title= Upper Ordovician Brachiopods from Poland and Britain|journal= Acta Palaeontologica Polonica|volume=10|pages=379–450|url= https://paleodb.org/cgi-bin/bridge.pl?a=displayCollResults&taxon_no=19186&max_interval=Ordovician&country=Poland&is_real_user=1&basic=yes&type=view&match_subgenera=1}}</ref> of Wales (North Wales Rawtheyan Assemblage 4C, Crugan Mudstone and Duyfor Mudstone fauna, 53.0° N, 4.0° W;<ref>{{cite journal|last= Price|first=D.|year=1981|title= Ashgill trilobite faunas from the Llyn Peninsula, North Wales, U.K|journal= Geological Magazine|volume=16|issue=3|pages=201–216|url= https://paleobiodb.org/classic/displayCollResults?collection_no=3666|doi=10.1002/gj.3350160305|bibcode=1981GeolJ..16..201P |url-access=subscription}}</ref> Rhwlas Limestone Formation<ref>{{cite journal|last1= Bassett|first1= D.A.|last2= Whittington|first2= H.B.|last3= Williams|first3= A.|year= 1966|title= The Stratigraphy of the Bala District, Merionethshire|journal= Quarterly Journal of the Geological Society of London|volume=122|issue=3|url= https://paleobiodb.org/classic/displayCollResults?collection_no=3675|doi=10.1144/gsjgs.122.1.0219|pages=219–269|s2cid= 128598649|url-access= subscription}}</ref> and ''Opsimasaphus''-''Nankinolithus'' trilobite association,<ref>{{cite journal|last1= Price|first1=D. |last2= Magor|first2=P.M.|year=1984|title= The ecological significance of variation in the genesis composition of Rawtheyan (Late Ordovician) trilobite faunas from North Wales, U.K|journal=Geological Journal|volume= 19|issue=2 |pages=187–200|url= https://paleobiodb.org/classic/displayCollResults?collection_no=3676|doi=10.1002/gj.3350190207|bibcode=1984GeolJ..19..187P |url-access=subscription}}</ref> 53.0° N, 3.0° W; Pontyfeni Formation, ''B. rushtoni'' and ''Stapeleyella abyfrons'' biozone, Whitland, 52.0° N, 5.0° W)<ref>{{cite journal|last1= Fortey|first1=R. A.|authorlink = Richard Fortey|last2= Owens|first2= R.M.|year=1978|title= Early Ordovician (Arenig) stratigraphy and faunas of the Carmarthen District, South-West Wales|journal= Bulletin of the British Museum (Natural History), Geology Series|volume= 30|issue= 3|pages= 225–294|url= https://paleobiodb.org/classic/displayCollResults?collection_no=3704}}</ref> and Scotland (Costonian, Superstes Mudstone, Stinchar River tributary, Colmonell, Gircan District, Strathclyde, 57.0° N, 4.0° W).<ref>{{cite journal|last1= Tripp|first1= R.P.|last2= Williams|first2= A.|last3= Paul|first3=C.R.C.|year= 1981|title= On an exposure of the Ordovician superstes Mudstones at Colmonell, Gircan District, Strathclyde|journal= Scottish Journal of Geology|volume=17|issue= 1|pages=21–25|url=https://paleobiodb.org/classic/displayCollResults?collection_no=76076|doi=10.1144/sjg17010021|bibcode= 1981ScJG...17...21T|s2cid= 128426864|url-access= subscription}}</ref>

== Development == ''Trinodus elspethi'', which - as an agnostoid - only has two thorax segments, has at least nine larval stages (or instars), three meraspid and six holaspid, in its life. So it molted at least eight times.<ref name='Treatise'>Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997</ref>

== References == {{Reflist|32em}}

Category:Agnostida genera Category:Agnostoidea Category:Ordovician trilobites Category:Fossils of Canada Category:Fossils of the United States Category:Fossils of Italy Category:Fossils of the Czech Republic Category:Fossils of Poland Category:Fossils of Denmark Category:Fossils of Sweden Category:Fossils of Svalbard Category:Fossils of Ireland Category:Fossils of Great Britain Category:Fossils of Iran Category:Fossils of Kazakhstan Category:Fossils of China Category:Paleontology in Yukon Category:Paleozoic life of the Northwest Territories Category:Taxa named by Frederick McCoy Category:Paleozoic life of Yukon