Biology:Isotelus

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  • Type species Isotelus gigas Dekay, 1824 – The type species of Isotelus, first described by James Ellsworth De Kay. This is one of the two species present in the Cincinnatian strata of Ohio, alongside I. maximus. It is differentiated by its much smaller adult size, its thinner profile, a broadly triangular cephalon and pygidium, and an absence of genal spines in larger adults. This species is also found in Iowa, Indiana, Wisconsin, Kentucky, Michigan, Missouri, New York, Pennsylvania, Ontario, Quebec, and Nunavut.[1]
  • Isotelus copenhagenensis Ross Jr. & Shaw 1972 – Named after the Copenhagen Formation strata where it was discovered in Nevada.[2]
  • Isotelus kimmswickensis Bradley 1930 – Species with a very short cephalon, found in the Goetz quarry in Missouri.[3]
  • Isotelus homalonotoides Walcott 1877 – From the Decorah Shale.
  • Isotelus violaensis Amati 2014 – Found in the Viola Springs Formation of Oklahoma.[4][5]

Group 2

This group is defined by a cranidium which "narrows strongly immediately in front of the palpebral lobes and widens gradually as the facial sutures curve gently forward and outward; the widest point of the cranidium in front of the palpebral lobes is at the inflection point where the facial sutures turn to become directed inward to the mid-line".[5] In simpler terms, the isolated cranidium in this group appears more arrow-shaped, with the sutures constricting inwardly anterior to the eyes. This suture pattern is also seen in Isoteloides, and is thus thought to be a plesiomorphic trait compared to apomorphic suture pattern of Group 1.

  • Isotelus parvirugosus Chatterton & Ludvigsen 1976 – Found in the Northwest Territories of Canada.
  • Isotelus dorycephalus Hunda et al.. 2003 – Also found in the Northwest Territories of Canada.
  • Isotelus iowensis Owen 1852 – Found in Illinois, Iowa, Michigan, Minnesota, Missouri, Ontario, and Nunavut.[6]
  • Isotelus walcotti Walcott 1918 – (Junior synonym I. planus) Found in Iowa, Wisconsin, and New York.[7]
  • Isotelus giselae Tripp and Evitt 1986 – Known from Virginia.[8]
  • Isotelus bradleyi Amati 2014 – Also found in the Viola Springs Formation of Oklahoma.[9][5]
  • Isotelus skapaneidos Amati 2014 – Named for its shovel-shaped cranidium, known from Oklahoma.[5]

Group 3

The third grouping proposed by Amati has a similar suture profile to Group 2, but are very wide relative to their length, and have shorter, rounded pygidiums with broad borders. Amati suggests that this group, if a phylogenetic analysis were performed, would not clade with the other species of Isotelus (which would clade closer to the genus Ectenaspsis), and thus may warrant a new genus to contain them. For now, they are referred to as "Isotelus".[5]

  • Isotelus maximus Locke 1838 – One of the two Isotelus species present in the Cincinnatian strata of Ohio, alongside I. gigas. This species a much greater maximum size, and is easily differniated by its semi-circular cephalon and pygidium, and by the larger genal spines which are present in all adult specimens. In addition to Ohio, this species is found in Illinois, Indiana, Kentucky, Virginia, Missouri, Ontario, and Manitoba.[10]
  • Isotelus rex Rudkin et al.. 2003 – The largest species of Isotelus, known from fragmentary specimens and rare complete individuals. The mostly complete holotype specimen of I. rex, from Churchill River Group, Churchill, Manitoba, is the largest complete trilobite ever found. Discovered by Dave Rudkin (Royal Ontario Museum), Robert Elias (University of Manitoba), Graham Young (Manitoba Museum) and Edward Dobrzanske (Manitoba Museum) in 1999, it measures 720 millimetres (28 in) in length, 400 millimetres (16 in) in maximum width (across the cephalon) and 70 millimetres (3 in) in maximum height (at the posterior midpoint of the cephalon). As an adult, this species lacked genal spines entirely, and is differentiated by its narrower body and more widely spaced eyes.[11][12] It was probably exceeded in size only by Hungioides bohemicus, in which the specimens probably exceeding I. rex in size are only known from partial remains.[13]
  • Isotelus latus Raymond 1913 – Defined by a concave cephalic border, widest at the anterior.
  • Isotelus ottawaensis Wilson 1947 – Eyes close to the posterior of the cephalon and close together, found in the Ottawa Formation.[citation needed]

References

  1. ↑ Template:Cite PBDB
  2. ↑ Template:Cite PBDB
  3. ↑ Template:Cite PBDB
  4. ↑ Template:Cite PBDB
  5. ↑ 5.0 5.1 5.2 5.3 5.4 Cite error: Invalid <ref> tag; no text was provided for refs named amati2014
  6. ↑ Template:Cite PBDB
  7. ↑ Template:Cite PBDB
  8. ↑ Tripp, R. P; Evitt, W. R. (1986). "Silicified trilobites of the family Asaphidae from the Middle Ordovician of Virginia". Palaeontology 29: 705–724. 
  9. ↑ Template:Cite PBDB
  10. ↑ Template:Cite PBDB
  11. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named dmr
  12. ↑ S. M. Gon III (2005-08-17). "The World's Largest Trilobites". http://www.trilobites.info/lgtrilos.htm. 
  13. ↑ Gutiérrez-Marco, Juan C.; Sá, Artur A.; García-Bellido, Diego C.; Rábano, Isabel; Valério, Manuel (2009). "Giant trilobites and trilobite clusters from the Ordovician of Portugal". Geology 37 (5): 443–446. doi:10.1130/g25513a.1. ISSN 1943-2682. Bibcode: 2009Geo....37..443G. http://dx.doi.org/10.1130/G25513A.1. 

Wikidata ☰ Q44087 entry



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