Systematics of the Ordovician trilobites Ischyrotoma and Dimeropygiella, with species from the type Ibexian area, western U.S.A.

Author:

Adrain Jonathan M.,Westrop Stephen R.,Landing Ed,Fortey Richard A.

Abstract

Lower Ordovician sections in the type Ibexian area of western Utah contain a considerably more diverse trilobite fauna than has previously been reported. Reinvestigation of these faunas, based on new field sampling, allows a reassessment of the dimeropygid genera Ischyrotoma Raymond, 1925, and Dimeropygiella Ross, 1951. These taxa have been considered synonyms, but parsimony analysis indicates each is a well supported clade, and they are best recognized as sister genera. The number of species known from Ibex has been doubled, from four to eight, and morphological information is now available for most parts of the exoskeleton. New species include Ischyrotoma juabensis (Juab Formation), I. wahwahensis (Wah Wah Formation), Dimeropygiella fillmorensis (Fillmore Formation), and D. mccormicki (Fillmore Formation). The previously named species Dimeropygiella caudanodosa, D. blanda, and D. ovata are fully revised on the basis of abundant new material. Pseudohystricurus is a paraphyletic group, with species distributed as a basal grade of the Ischyrotoma/Dimeropygiella group.

Publisher

Cambridge University Press (CUP)

Subject

Paleontology

Reference56 articles.

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4. Ordovician trilobites from the Tourmakeady Limestone, western Ireland. Bulletin of the Natural History Museum, London;Adrain;Geology Series,1997

5. An Ordovician (Arenigian) trilobite faunule of great diversity from the Ibex area, western Utah;Young;Brigham Young University Geology Studies,1973

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