Trinodus
Temporal range: Ordovician
A drawing of "Trinodus tardus"
A drawing of Trinodus tardus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: †Trilobita (?)
Order: †Agnostida
Family: †Metagnostidae
Genus: †Trinodus
M'Coy, 1846
Type species
†Trinodus agnostiformes
M'Coy, 1846
Species
  • †Trinodus agnostiformes M'Coy, 1846 synonyms A. agnostiformis, A. trinodus
  • †Trinodus tardus (Barrande,1846) synonyms Battus tardus, Agnostus glabratus, A. tardus[1] Arthrorhachis tarda, alternative spelling A. tardus
  • †Trinodus elspethi (Raymond, 1925) synonym Arthrorhachis elspethi
  • †Trinodus danicus Poulsen, 1965 synonym Arthrorhachis danica
  • †Trinodus girvanensis (Reed, 1903) synonyms Agnostus girvanensis, Arthrorhachis girvanensis, Girvanagnostus girvanensis
  • †Trinodus hupehensis Lu, 1975 synonym Arthrorhachis hupehensis
  • †Trinodus knockerkensis Romano & Owen, 1993 synonym Arthrorhachis knockerkensis
  • †Trinodus latilimbata (Ju in Qiu et al., 1983)synonym Arthrorhachis latilimbata
  • †Trinodus pragensis (Přibyl & Vaněk, 1968) synonym Arthrorhachis pragensis
Synonyms
  • †Arthrorhachis
  • †Girvanagnostus
  • †Metagnostus

Trinodus is a very small to small (about 1 centimetre or 0.39 inches) blind trilobite, a well known group of extinct marine arthropods, which lived during the Ordovician (Tremadocian to early Hirnantian),[1] 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).[1]

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.[2]

Species previously assigned to Trinodus

Distribution

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.[18]

References

  1. ^ a b c d e Budil, P.; Fatka, O.; Kolář, P.; David, M. (2011). "Arthrorhachis Hawle & Corda, 1847 (Agnostida) in the Prague Basin revisited" (PDF). Bulletin of Geosciences. 86 (4): 707–724. doi:10.3140/bull.geosci.1262.
  2. ^ a b Turvey, S.T. (2005). "Agnostid trilobites from the Arenig-Llanvirn of South China". Transactions of the Royal Society of Edinburgh: Earth Sciences. 95 (3–4): 527–542. doi:10.1017/s026359330000119x. S2CID 130775617.
  3. ^ a b Karim, T.S. (2009). "Ordovician trilobites from Iran". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 99 (2): 101–124. doi:10.1017/s1755691009007063. S2CID 129780250.
  4. ^ Fortey, R. A. (1980). "The Ordovician trilobites of Spitsbergen. III. Remaining trilobites of the Valhallfonna Formation". Norsk Polarinstitutt Skrifter. 171: 1–163.
  5. ^ Romano, M.; Owen, A. W. (1993). "Early Caradoc Trilobites of Eastern Ireland and their paleogeographical significance". Palaeontology. 36 (3): 681–720.
  6. ^ a b c d Ahlberg, P. (1989). "Agnostid trilobites from the Upper Ordovician of Sweden and Bornholm, Denmark" (PDF). Bulletin of the Geological Society of Denmark. 37: 213–226. doi:10.37570/bgsd-1988-37-17.
  7. ^ Chlupac, I.; Havlicek, V.; Kukal, Z.; Storch, P. (1998). Palaeozoic of the Barrandian (Cambrian to Devonian). pp. 1–183.
  8. ^ Leone, F.; Hammann, W.; Laske, R.; Serpagli, E.; Villas, E. (1991). "Lithostratigraphic units and biostratigraphy of the post-sardic Ordovician sequence in south-west Sardinia". Bollettino della Societá Paleontologica Italiana. 30: 201–235.
  9. ^ Havlicek, V.; Vanek, J. (1990). "Ordovician Invertebrate communities in black-shale lithofacies (Prague Basin, Czechoslovakia)". Vestnik Ustredniho Ustavu Geologickeho. 65: 223–236.
  10. ^ Ludvigsen, R. (1981). "Biostratigraphical significance of Middle Ordovician trilobites from the Road River Formation, northern Cordillera". Geological Association of Canada, Abstracts. 6 (A-36).
  11. ^ Stratigraphic Group of Yunnan, China (1978). Regional stratigraphic data of Southwest China, Yunnan Province. Beijing: Geological Publishing House.
  12. ^ Temple, J.T. (1965). "Upper Ordovician Brachiopods from Poland and Britain". Acta Palaeontologica Polonica. 10: 379–450.
  13. ^ Price, D. (1981). "Ashgill trilobite faunas from the Llyn Peninsula, North Wales, U.K". Geological Magazine. 16 (3): 201–216. Bibcode:1981GeolJ..16..201P. doi:10.1002/gj.3350160305.
  14. ^ Bassett, D.A.; Whittington, H.B.; Williams, A. (1966). "The Stratigraphy of the Bala District, Merionethshire". Quarterly Journal of the Geological Society of London. 122 (3): 219–269. doi:10.1144/gsjgs.122.1.0219. S2CID 128598649.
  15. ^ Price, D.; Magor, P.M. (1984). "The ecological significance of variation in the genesis composition of Rawtheyan (Late Ordovician) trilobite faunas from North Wales, U.K". Geological Journal. 19 (2): 187–200. Bibcode:1984GeolJ..19..187P. doi:10.1002/gj.3350190207.
  16. ^ Fortey, R. A.; Owens, R.M. (1978). "Early Ordovician (Arenig) stratigraphy and faunas of the Carmarthen District, South-West Wales". Bulletin of the British Museum (Natural History), Geology Series. 30 (3): 225–294.
  17. ^ Tripp, R.P.; Williams, A.; Paul, C.R.C. (1981). "On an exposure of the Ordovician superstes Mudstones at Colmonell, Gircan District, Strathclyde". Scottish Journal of Geology. 17 (1): 21–25. Bibcode:1981ScJG...17...21T. doi:10.1144/sjg17010021. S2CID 128426864.
  18. ^ Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997
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