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

Published online by Cambridge University Press:  20 May 2016

Jonathan M. Adrain ,
Stephen R. Westrop ,
Ed Landing  and
Richard A. Fortey
Jonathan M. Adrain
Affiliation:
1Department of Geoscience, University of Iowa, 121 Trowbridge Hall, Iowa City 52242, and Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom
Stephen R. Westrop
Affiliation:
2Oklahoma Museum of Natural History and School of Geology and Geophysics, University of Oklahoma, Norman 73019,
Ed Landing
Affiliation:
3Center for Stratigraphy and Paleontology, New York State Museum, The State Education Department, Albany, New York 12230,
Richard A. Fortey
Affiliation:
4Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom,
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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.

Type
Research Article
Information
Journal of Paleontology , Volume 75 , Issue 5 , September 2001 , pp. 947 - 971
Copyright
Copyright © The Paleontological Society

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