Abstract
The first records of the upper Cambrian agnostoid generaKormagnostella, E. Romanenko,inRomanenko and Romanenko, 1967, andBiciragnostusF. Ergaliev,inEraliev and Ergaliev, 2001, in Laurentian North America are from a narrow stratigraphic interval in the Steptoean–Sunwaptan boundary interval (Furongian, Jiangshanian) of Nevada and Utah. In Nevada, both genera occur in a condensed bioclastic lag below a major flooding surface, andKormagnostellaalso appears in a transgressive interval in Utah. Immigration of these genera is associated with sea level rise, and also with faunal turnover.Biciragnostusis confined to the latestElviniaZone, immediately below the onset of a trilobite and agnostoid extinction event at the base of theIrvingella majorZone (basal Sunwaptan).Kormagnostellais present in the latestElviniaZone, and has its highest occurrence in theI. majorZone. Stratigraphic data from the Karatau-Naryn Terrane, Kazakhstan indicate that both genera disappear near the local extinction ofIrvingella, suggesting that faunal turnover in that region may have been broadly correlative with the more profound extinction in Laurentia. New species areKormagnostella advena,K. insolitaandBiciragnostus viator.
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