Trinodus

{{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{{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}} 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), 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).

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.{{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}}

= 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).{{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 }}
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).{{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}}
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).
T. hupehensis has been found in the Middle Ordovician of China (Dawan Formation, upper Arenig, Fenxiang, Yichang County, West Hubei).
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).{{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}}
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.
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),{{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}} 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 Ostergotland: Råssnås and Rodbergsudden, both near MotalaIn. In Våstergotland: 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 (Hogstenaberget); Skultorp, Billingen; Rustsåter, Kinnekulle; Kullatorp core, Kinnekulle. In Dalarna: Vikarbyn and Gulleråsen-Sanden) of Norway (Oslo Region, Hovedøya, Spannslokket Member of the Skogerholmen Formation; Åslund, Hadeland Gagnum Shale Member of the Lunner Formation) of the Czech Republic (upper Katian, Tretaspis seticornis community, Kraluv Dvur Formation),{{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}} of Italy (Foliomena community, Domusnovas Formation, Punta S'Argiola, Sardinia, 40.0° N, 8.0° E),{{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}} of Iran (late Caradoc, early Asgill, Tatavrud, 35 km southwest of Bandar-e-Anzali), and of Kazakhstan.
Trinodus sp. (presumably T. tardus) has been collected from the Ordovician of Czech Republic (Králův Dvůr Formation, Prague Basin).{{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}}
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),{{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}} of China (Baota (Pagoda) Formation, NingLang, NingLang County, Yunnan),{{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)}} of Poland (Hirnantian, Holycross Mountains, 51.0° N, 21.0° E),{{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}} of Wales (North Wales Rawtheyan Assemblage 4C, Crugan Mudstone and Duyfor Mudstone fauna, 53.0° N, 4.0° W;{{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 }} Rhwlas Limestone Formation{{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}} and Opsimasaphus-Nankinolithus trilobite association,{{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 }} 53.0° N, 3.0° W; Pontyfeni Formation, B. rushtoni and Stapeleyella abyfrons biozone, Whitland, 52.0° N, 5.0° W){{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}} and Scotland (Costonian, Superstes Mudstone, Stinchar River tributary, Colmonell, Gircan District, Strathclyde, 57.0° N, 4.0° W).{{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}}

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.Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997