Affinities of the lower Ordovician (Tulean; lower Floian) trilobite Gladiatoria, with species from the Great Basin, western United States

Macropyge gladiator Ross, 1951a, is the type species of the previously monotypic Gladiatoria Hupé, 1955. It has been regarded as the only known post-Tremadocian macropygine ceratopygid, and the only known ceratopygid from the Ordovician of Laurentia. Well preserved new material from western Utah and southern Idaho includes the first positively identified cephalic sclerites and demonstrates that Gladiatoria is a component of Bathyuridae, a family common in shallow water Lower Ordovician assemblages from Laurentia. Gladiatoria is closely related to and regarded as the sister taxon of Bathyurellus Billings, 1865, to which it is nearly identical in cephalic morphology. In addition to an extended revision of the type species, which is from the lower Psalikilopsis cuspidicauda Zone, new species described include G. phoenixi (Hintzeia celsaora Zone), G. nielsenae (Psalikilopsis cuspidicauda Zone and Psalikilus typicum Zone), G. harrisi (upper Psalikilopsis cuspidicauda Zone), G. reedi (Psalikilus typicum Zone and Psalikilus hestoni Zone) and G. crowei (Protopliomerella contracta Zone). All are from the Tulean Stage (lower Floian).