Observations on the Attawapiskat Formation (Silurian) trilobites of Ontario, with description of a new encrinurine

Gass, Kenneth C.; Mikulic, Donald G.

doi:10.1139/e82-047

Cited by 7 publications

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“…This group was diagnosed by Strusz (1980, p. 45) on the following basis: "glabella is narrow-based and widens strongly forward, while the pygidium becomes larger and more elongate, subtriangular in outline, with a narrow rachis often of more than twenty rings, and truncate pleural tips not significantly turned out." Encrinuroides (s.s.) could be restricted to this group; its monophyly is conditional on the exclusion of Cromus Barrande, 1852and Perryus Gass and Mikulic, 1982(Gass and Mikulic (1982 and Edgecombe et al (1988) suggested that these genera might be most closely related to Encrinuroides (s. s .)). Strusz's (1980) phylogenetic hypothesis accommodates the reassignment of several other parts of the "Encrinuroides" paraphylum.…”

Section: Encrinuroides (Ss) and Physemataspismentioning

confidence: 97%

Systematics of Encrinuroides and Curriella (Trilobita), with a new Early Silurian encrinurine from the Mackenzie Mountains

Edgecombe¹,

Chatterton²

1990

Can. J. Earth Sci.

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has been diagnosed as a paraphyletic ancestral taxon since its inception. Cladistic parsimony analysis of "Encrinuroides" species most closely related to the Silurian Encrinurus plexi discovers two shortest-length cladograms (consistency index = 0.68) based on 28 exoskeletal characters. Curriella Lamont, 1978 is revised to include Curriella clancyi n.sp., based on silicified material from earliest Llandovery strata of the Whittaker Formation in the Mackenzie Mountains, Northwest Territories. The new species is most closely related to the Scottish Llandovery type species, Curriella newlandensis Lamont, 1978 (for which type specimens are figured) and Curriella tuberculifrons (Weller, 1907) from Illinois. This Silurian clade is sister group to stratigraphically early Chinese "Encrinuroides" species and the monophyletic Encrinurus plexi. Certain Appalachian Caradoc taxa and Erratencrinurus Krueger, 1972 are more closely related to this group than to many other "Encrinuroides" spp. Further taxonomic revision should exclude these species from Encrinuroides (s.s.), which can be appreciably restricted in scope.Encrinuroides Reed, 1931 a Ct C diagnostiquke dbs sa dkcouverte comme un taxon ancestral paraphylCtique. Une analyse cladistique parcimonieuse de l'esptce << Encrinuroides >>, dont le plus proche parent est Encrinurus plexi du Silurien, indique deux cladogrammes courtes branches (index de consistance = 0,68) fond& sur 28 caracttres d'exosquelettes. Curriella Lamont, 1978 a Ct C rCvisCe de manitre a inclure Curriella clancyi n.sp., suite a une Ctude de matBrie1 silicifiC recueilli dans les strates du Llandovery de la Formation de Whittaker, dans les monts Mackenzie des Territoires du Nord-Ouest. La nouvelle e s g c e a pour plus proches parents l'esgce-type Curriella newlandensis Larnont, 1978 du Llandovery de 1'Ecosse (dont les spt5cimens types sont illustrCs) et Curriella tuberculifrons (Weller, 1907) de 1'Illinois. Le cladogramme silurien reprksente des espbces trbs Ctroitement apparentkes a Encrinuroides et 21 Encrinurus plexi monophyl6tique. Certains taxons du Caradoc des Appalaches et Erratencrinurus Krueger, 1972 sont plus apparentkes avec ce groupe qu'avec plusieurs autres << Encrinuroides >> spp. Les rCvisons taxonomiques futures devraient exclure ces esgces d'Encrinuroides (s.~.), lesquelles couvriraient une ttendue considkrablement plus restreinte. [Traduit par la revue]Can.

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Section: Encrinuroides (Ss) and Physemataspismentioning

confidence: 97%

Systematics of Encrinuroides and Curriella (Trilobita), with a new Early Silurian encrinurine from the Mackenzie Mountains

Edgecombe¹,

Chatterton²

1990

Can. J. Earth Sci.

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“…The randomness of the distribution of glabellar tubercles on even the posterior parts of the glabella is unusual, although it is seen in some species of what may be the related genera Cromus Barrande, 1852 and Perryus Gass & Mikulic, 1982. Such a random arrangement is presumably a convergent character since it is also seen on the anterior parts of some species of Frammia Holtedahl, 1914, Encrinuroides Reed, 1931 and Encrinurus species such as E. hagshawensis Lamont, 1965 (see Howells, 1982, pI.…”

Section: Diseussion a Combination Of Distinctive Characters Warrants The Erection Of This New Genusmentioning

confidence: 99%

Silurian trilobites from Peary Land, central North Greenland

Lane¹

1988

rapggu

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Five species of trilobites are described from near the top of the Odins Fjord Formation in Peary Land: Opoa ostreata sp. nov., Encrinuroides palasso sp. nov. (for comparison with which the type series of Encrinuroides moderatus (Poulsen, 1934) is refigured), Distyrax peeli gen. et sp. nov. (Encrinuridae), Podowrinella christiei sp. nov. and Gaotania anoplos sp. nov. The age of the fauna and links with other faunas are discussed.

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Stasis and extinction of Silurian (Llandovery–Wenlock) trilobite associations related to oceanic cyclicity

Mikulic

Kluessendorf

1999

J. Paleontol.

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Silurian trilobites of the central United States belong to a series of temporally-successive associations which appeared abruptly, maintained taxonomic stasis for a time, and then disappeared abruptly. Their disappearance resulted from global perturbations of short-term duration and moderate magnitude, which caused substantial taxonomic replacement but no reorganization of major ecosystems. The most significant extinction and replacement in Silurian trilobite associations in the study area occurs near the Llandovery–Wenlock boundary. This turnover in trilobite associations appears to correspond to Jeppsson's Ireviken Event in his model of oceanic and climatic cyclicity. Major sea-level changes earlier in the Llandovery did not have a similar impact on trilobite associations.

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Observations on the Attawapiskat Formation (Silurian) trilobites of Ontario, with description of a new encrinurine

Cited by 7 publications

References 0 publications

Systematics of Encrinuroides and Curriella (Trilobita), with a new Early Silurian encrinurine from the Mackenzie Mountains

Systematics of Encrinuroides and Curriella (Trilobita), with a new Early Silurian encrinurine from the Mackenzie Mountains

Silurian trilobites from Peary Land, central North Greenland

Stasis and extinction of Silurian (Llandovery–Wenlock) trilobite associations related to oceanic cyclicity

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