Marjuman (Cambrian) agnostoid trilobites of the Cow Head Group, western Newfoundland

Abstract

Shelf-derived limestone boulders in debris flows of the Cow Head Group, western Newfoundland, have yielded rich mid- to Upper Cambrian trilobite faunas. The agnostoid component of Marjuman boulders consists of 23 species assigned to 11 genera;Kormagnostus boltoniandKormagnostus?copelandiare new. Cladistic parsimony analysis of the Ptychagnostidae Kobayashi reduces this family to 3 genera:PtychagnostusJaekel,PseudophalacromaPokrovskaya andLejopygeHawle and Corda;Ptychagnostusincludes three non-obligate subgenera:P. (Ptychagnostus) (= TomagnostusHowell);P. (Goniagnostus) Howell andP. (Aotagnostus) öpik (=Myrmecomimusöpik). Correlation with zonations established in northern Canada and Utah indicates that the Cow Head Group includes a nearly complete sequence of agnostoid faunas from the mid-CambrianPtychagnostus gibbusZone to the Upper MarjumanCedaria brevifronsZone.