01845nas a2200205 4500008004100000245013000041210006900171300001200240490000700252520119600259653001701455653002101472653001501493653001701508100001901525700002001544700001601564700001901580856004001599 2001 eng d00aSystematics of the Ordovician Trilobites Ischyrotoma and Dimeropygiella, With Species from the Type Ibexian Area, Western USA0 aSystematics of the Ordovician Trilobites Ischyrotoma and Dimerop a947-9710 v753 a

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.

10aIbexian area10aLower Ordovician10atrilobites10awestern Utah1 aAdrain, J., M.1 aWestrop, S., R.1 aLanding, E.1 aFortey, R., A. uhttp://www.jstor.org/stable/1307060