Triarthrus is a genus of Upper Ordovicianptychopariidtrilobite found in New York, Ohio, Kentucky, and Indiana, eastern and northern Canada, China and Scandinavia. It is the last of the Olenid trilobites, a group which flourished in the Cambrian period. The specimens of T. eatoni that are found in the Beecher's Trilobite Bed, Rome, New York area are exquisitely preserved showing soft body parts in iron pyrite. Pyrite preservation has given scientists a rare opportunity to examine the gills, walking legs, antennae, digestive systems, and eggs of trilobites, which are rarely preserved. Triarthrus is therefore commonly used in science texts to illustrate trilobite anatomy and physiology.
T. beckii Upper Caradoc and Ashgill, Snake Hill Formation, Cohoes, New York State; and Kentucky.
T. billingsi Ashgill?, Quebec
T. canadensis is known from the Upper Ordovician of Canada (Katian, lower Member of the Whitby Formation, Craigleith vicinity, Georgian Bay area; middle Member of the Whitby Formation, Whitby, Rogue River and Pickering, all Lake Simcoe area, Ontario)[1]
T. eatoni Upper Caradoc-Ashgill, N.Y., is known from the Upper Ordovician of Canada (Ashgill, lower Member of the Whitby Formation, Craigleith vicinity, Georgian Bay area, Lake Simcoe area, Ontario;[1] and Quebec) and the United States (New York)
T. glaber Ashgill, Quebec
T. huguesensis Ashgill, Quebec
T. latissimus Sweden
T. linnarssoni Norway and Sweden
T. rougensis Ashgill, Ontario
T. sichuansis China
T. spinosus is known from the Upper Ordovician of Canada (Katian, middle Member of the Whitby Formation, Rogue River and Pickering, both Lake Simcoe area, Ontario[1] and Quebec), and the United States (New York).
Taxonomy
Cladogram showing the assumed relationships and known temporal distribution of the genera Bienvillia, Porterfieldia and Triarthrus, family Olenidae[2]
T. beckii and T. eatoni have long been considered closely related and possibly synonymous. Recent comparative analysis showed that there is no sharp distinction between the two, but that they seem to represent opposing morphotypes. T. beckii dominates earlier in the distribution and in shallow water, while T. eatoni does so later and in deeper waters. It is probable that the transgression of the sea level aided the eventual disappearance of the T. beckii morph. The occurrence of the supposed pluriform species continued for more than two million years.[3]
Reconstruction of Triarthrus eatoni, showing the appendages
Pyrite preserved Triarthrus eatoni - ventral side
Triarthrus is an average size trilobite (up to about 5 centimetres or 2.0 inches) and its moderately convex body is about twice as long as wide (excluding spines). Like in all Olenidae, the headshield (or cephalon) of Triarthrus has opisthopariansutures, and the right and left free cheeks that they define are yoked. The cephalon in Triarthrus is semicircular. The central raised area (or glabella) is approximately quadrate, and considerably wider than the posterior margin of the fixed cheeks (or fixigenae). The front of the glabella is close to the anterior border (or the preglabellar field is short), but the border furrow is absent in front of the glabella. The facial suture crosses in front of the glabella on the top of an inflated rim. The posterior end of the glabella consists of the occipital ring that is defined by a furrow crossing over the midline. The occipital ring carries a small node at its centre point, and may be adorned with a backward directed spine as long as the glabella. In front of the occipital furrow two pairs of lateral furrows emerge from the axial furrow almost perpendicularly and curve backwards as they cut toward the midline, but without reaching it. Anteriorly, one or two further furrows are isolated shallow slits or depressions. The fixigenae are very narrow (less than ¼ of the width of the glabella at the back of the eye, and less than ½ at the occipital ring). The librigenae are narrow, and with or without spines. The border is prominent elsewhere, and the eyes of small to medium size, sitting at the end of small palpebral lobes next to the frontal half of the glabella. The thorax consists of 13 to 16 segments, with the axis wider than pleural regions, obliquely truncated or rounded pleural tips, and the fulcrum placed very close to the axis. The tailpiece (or pygidium) is small, with 3 to 5 axial rings, distinctly segmented pleural fields, and an entire, evenly rounded margin.[2][4]
Uncalcified parts
The foremost pair of extremities in trilobites are the antennas. In Triarthrus eatoni the antennas are probably flexible. From their attachment adjacent to the hypostome they stretch inward and forward, almost touching each other at the point where, from a dorsal viewpoint, they appear from under the cephalic margin, then bending outward and then forward again in a slight S-curve. They are about twice as long as the headshield (or cephalon), each consisting of 40 to 50 segments that are shorter than wide. As the preservation of soft tissue in T. eatoni is excellent, it is probable that it lacked cerci, the most backward pair of extremities known from Olenoides serratus.[4][5][6][7]
Life cycle
Due to the existence of an excellently preserved deposit in the Frankfurt Shale near Rome, New York State, that suggests an entire population of Triarthrus eatoni was killed and quickly buried, it has been possible to make a plausible reconstruction of its life history. After hatching from roughly spherical eggs averaging ~0.2mm in diameter, the small protaspid and early meraspid stages supposedly lived between the plankton in the water column. This is derived from the fact that only exuviae of the early stages were found, making clear that they haven't died in the disaster that killed their elders. In this phase the larvae probably got dispersed over large areas. After a few months, at about 2mm long T. eatoni started living at the sea floor. Here, it must have fed by filtering suspended food particles, probably comparable to the trunk limb filter-feeding Cephalocarida and Branchiopoda. The exoskeletons fall into five size categories, suggesting that T. eatoni had a distinct breeding season, likely annually, as is the case in almost all extantcrustaceans (although some amphipods have two breeding periods per year). It could live through at least four breeding seasons, and at that age reach approximately 4 cm in length.[8][9]
References
^ abcLiberty, B.A. (1969). "Palaeozoic geology of the Lake Simcoe Area, Ontario". Geological Survey of Canada Memoirs (355): 1–201. cited in Paleobiology Database. "Triarthrus canadensis". Retrieved 13 November 2013.
^ abcLudvigsen, R.; Tuffnell, P.A. (1983). "A revision of the Ordovician olenid trilobite Triarthrus". Geological Magazine. 120 (6): 567–577. doi:10.1017/s0016756800027722.
^Cisne, John L.; Molenock, Joane; Rabe, Bruce D. (1980). "Evolution in a cline: the trilobite Triarthrus along an Ordovician depth gradient". Lethaia. 13 (1): 47–59. doi:10.1111/j.1502-3931.1980.tb01029.x.
^ abMoore, R.C. (1959). Arthropoda I - Arthropoda General Features, Proarthropoda, Euarthropoda General Features, Trilobitomorpha. Treatise on Invertebrate Paleontology. Vol. Part O. Boulder, Colorado/Lawrence, Kansas: Geological Society of America/University of Kansas Press. pp. 1–560. ISBN0-8137-3015-5.
^Beecher, C.E. (1893). "A larval form of Triarthrus". American Journal of Science. 46 (275): 361–362. Bibcode:1893AmJS...46..378B. doi:10.2475/ajs.s3-46.275.378. S2CID 131502904.
^Beecher, C.E. (1902). "The ventral integument of trilobites". American Journal of Science. Series 4. 13 (75): 165–173. Bibcode:1902AmJS...13..165B. doi:10.2475/ajs.s4-13.75.165.
^Cisne, John L. (1973). "Life History of an Ordovican [sic] Trilobite Triarthrus eatoni". Ecology. 54 (1): 135–142. doi:10.2307/1934382. JSTOR 1934382.
Thomas E. Whiteley, Gerald J. Kloc, and Carlton E. Brett Trilobites of New York. Cornell University Press, 2002. 456 pages. ISBN978-0-8014-3969-8
January 07, 2023
triarthrus, genus, upper, ordovician, ptychopariid, trilobite, found, york, ohio, kentucky, indiana, eastern, northern, canada, china, scandinavia, last, olenid, trilobites, group, which, flourished, cambrian, period, specimens, eatoni, that, found, beecher, t. Triarthrus is a genus of Upper Ordovician ptychopariid trilobite found in New York Ohio Kentucky and Indiana eastern and northern Canada China and Scandinavia It is the last of the Olenid trilobites a group which flourished in the Cambrian period The specimens of T eatoni that are found in the Beecher s Trilobite Bed Rome New York area are exquisitely preserved showing soft body parts in iron pyrite Pyrite preservation has given scientists a rare opportunity to examine the gills walking legs antennae digestive systems and eggs of trilobites which are rarely preserved Triarthrus is therefore commonly used in science texts to illustrate trilobite anatomy and physiology TriarthrusTemporal range Upper Ordovician PreꞒ Ꞓ O S D C P T J K Pg NTriarthrus eatoni 11mmScientific classificationKingdom AnimaliaPhylum ArthropodaClass TrilobitaOrder PtychopariidaFamily OlenidaeGenus TriarthrusGreen 1832SpeciesT beckii Green 1832 type species Paradoxides beckii Calymene beckiiT billingsi Barrande 1872T canadensis Smith 1861T eatoni Hall 1838 T macastyensisT glaber Billings 1859T huguesensis Forste 1924T latissimus Mansson 1998T linnarssoni Torslund 1940T rougensis Parks 1921T sichuansis Lu amp Chang 1974T spinosus Billings 1857 Contents 1 Distribution 2 Taxonomy 2 1 Species previously assigned to Triarthrus 3 Description 3 1 Exoskeleton 3 2 Uncalcified parts 4 Life cycle 5 References 6 Sources 7 Further readingDistribution EditT beckii Upper Caradoc and Ashgill Snake Hill Formation Cohoes New York State and Kentucky T billingsi Ashgill Quebec T canadensis is known from the Upper Ordovician of Canada Katian lower Member of the Whitby Formation Craigleith vicinity Georgian Bay area middle Member of the Whitby Formation Whitby Rogue River and Pickering all Lake Simcoe area Ontario 1 T eatoni Upper Caradoc Ashgill N Y is known from the Upper Ordovician of Canada Ashgill lower Member of the Whitby Formation Craigleith vicinity Georgian Bay area Lake Simcoe area Ontario 1 and Quebec and the United States New York T glaber Ashgill Quebec T huguesensis Ashgill Quebec T latissimus Sweden T linnarssoni Norway and Sweden T rougensis Ashgill Ontario T sichuansis China T spinosus is known from the Upper Ordovician of Canada Katian middle Member of the Whitby Formation Rogue River and Pickering both Lake Simcoe area Ontario 1 and Quebec and the United States New York Taxonomy Edit Cladogram showing the assumed relationships and known temporal distribution of the genera Bienvillia Porterfieldia and Triarthrus family Olenidae 2 T beckii and T eatoni have long been considered closely related and possibly synonymous Recent comparative analysis showed that there is no sharp distinction between the two but that they seem to represent opposing morphotypes T beckii dominates earlier in the distribution and in shallow water while T eatoni does so later and in deeper waters It is probable that the transgression of the sea level aided the eventual disappearance of the T beckii morph The occurrence of the supposed pluriform species continued for more than two million years 3 Species previously assigned to Triarthrus Edit T angelini Bienvillia angelini T belli Parabolinella sp T caenigenus Porterfieldia caenigena T convergens Porterfieldia convergens T fisheri Porterfieldia fisheri T goldwyerensis Porterfieldia goldwyerensis T humilis Porterfieldia humilis T jachalensis Porterfieldia jachalensis T pacificus Porterfieldia pacifica T papilosus Porterfieldia papilosa T parapunctatus Porterfieldia parapunctata T parchaensis Bienvillia parchaensis T punctatus Porterfieldia punctata T rectifrons Bienvillia rectifrons T reedi Porterfieldia caenigena T shinetonensis Bienvillia shinetonensis T sinensis Porterfieldia sinensis T tetragonalis Bienvillia tetragonalis T thor Porterfieldia thor T variscorum Parabolina frequens 2 Description EditExoskeleton Edit Reconstruction of Triarthrus eatoni showing the appendages Pyrite preserved Triarthrus eatoni ventral sideTriarthrus is an average size trilobite up to about 5 centimetres or 2 0 inches and its moderately convex body is about twice as long as wide excluding spines Like in all Olenidae the headshield or cephalon of Triarthrus has opisthoparian sutures and the right and left free cheeks that they define are yoked The cephalon in Triarthrus is semicircular The central raised area or glabella is approximately quadrate and considerably wider than the posterior margin of the fixed cheeks or fixigenae The front of the glabella is close to the anterior border or the preglabellar field is short but the border furrow is absent in front of the glabella The facial suture crosses in front of the glabella on the top of an inflated rim The posterior end of the glabella consists of the occipital ring that is defined by a furrow crossing over the midline The occipital ring carries a small node at its centre point and may be adorned with a backward directed spine as long as the glabella In front of the occipital furrow two pairs of lateral furrows emerge from the axial furrow almost perpendicularly and curve backwards as they cut toward the midline but without reaching it Anteriorly one or two further furrows are isolated shallow slits or depressions The fixigenae are very narrow less than of the width of the glabella at the back of the eye and less than at the occipital ring The librigenae are narrow and with or without spines The border is prominent elsewhere and the eyes of small to medium size sitting at the end of small palpebral lobes next to the frontal half of the glabella The thorax consists of 13 to 16 segments with the axis wider than pleural regions obliquely truncated or rounded pleural tips and the fulcrum placed very close to the axis The tailpiece or pygidium is small with 3 to 5 axial rings distinctly segmented pleural fields and an entire evenly rounded margin 2 4 Uncalcified parts Edit The foremost pair of extremities in trilobites are the antennas In Triarthrus eatoni the antennas are probably flexible From their attachment adjacent to the hypostome they stretch inward and forward almost touching each other at the point where from a dorsal viewpoint they appear from under the cephalic margin then bending outward and then forward again in a slight S curve They are about twice as long as the headshield or cephalon each consisting of 40 to 50 segments that are shorter than wide As the preservation of soft tissue in T eatoni is excellent it is probable that it lacked cerci the most backward pair of extremities known from Olenoides serratus 4 5 6 7 Life cycle EditDue to the existence of an excellently preserved deposit in the Frankfurt Shale near Rome New York State that suggests an entire population of Triarthrus eatoni was killed and quickly buried it has been possible to make a plausible reconstruction of its life history After hatching from roughly spherical eggs averaging 0 2mm in diameter the small protaspid and early meraspid stages supposedly lived between the plankton in the water column This is derived from the fact that only exuviae of the early stages were found making clear that they haven t died in the disaster that killed their elders In this phase the larvae probably got dispersed over large areas After a few months at about 2mm long T eatoni started living at the sea floor Here it must have fed by filtering suspended food particles probably comparable to the trunk limb filter feeding Cephalocarida and Branchiopoda The exoskeletons fall into five size categories suggesting that T eatoni had a distinct breeding season likely annually as is the case in almost all extant crustaceans although some amphipods have two breeding periods per year It could live through at least four breeding seasons and at that age reach approximately 4 cm in length 8 9 References Edit a b c Liberty B A 1969 Palaeozoic geology of the Lake Simcoe Area Ontario Geological Survey of Canada Memoirs 355 1 201 cited in Paleobiology Database Triarthrus canadensis Retrieved 13 November 2013 a b c Ludvigsen R Tuffnell P A 1983 A revision of the Ordovician olenid trilobite Triarthrus Geological Magazine 120 6 567 577 doi 10 1017 s0016756800027722 Cisne John L Molenock Joane Rabe Bruce D 1980 Evolution in a cline the trilobite Triarthrus along an Ordovician depth gradient Lethaia 13 1 47 59 doi 10 1111 j 1502 3931 1980 tb01029 x a b Moore R C 1959 Arthropoda I Arthropoda General Features Proarthropoda Euarthropoda General Features Trilobitomorpha Treatise on Invertebrate Paleontology Vol Part O Boulder Colorado Lawrence Kansas Geological Society of America University of Kansas Press pp 1 560 ISBN 0 8137 3015 5 Beecher C E 1893 A larval form of Triarthrus American Journal of Science 46 275 361 362 Bibcode 1893AmJS 46 378B doi 10 2475 ajs s3 46 275 378 S2CID 131502904 Beecher C E 1893 On the thoracic legs of Triarthrus American Journal of Science 46 467 470 Beecher C E 1902 The ventral integument of trilobites American Journal of Science Series 4 13 75 165 173 Bibcode 1902AmJS 13 165B doi 10 2475 ajs s4 13 75 165 Cisne John L 1973 Life History of an Ordovican sic Trilobite Triarthrus eatoni Ecology 54 1 135 142 doi 10 2307 1934382 JSTOR 1934382 pubs geoscienceworld org https pubs geoscienceworld org gsa geology article abstract 45 3 199 195237 Pyritized in situ trilobite eggs from the Retrieved 2022 08 13 a href Template Cite web html title Template Cite web cite web a Missing or empty title help Sources EditT eatoni and T rougensis photos Further reading EditThomas E Whiteley Gerald J Kloc and Carlton E Brett Trilobites of New York Cornell University Press 2002 456 pages ISBN 978 0 8014 3969 8 Retrieved from https en wikipedia org w index php title Triarthrus amp oldid 1107543240, wikipedia, wiki, book, books, library,
