The missisquoiid trilobite Parakoldinioidia Endo 1937 in the uppermost Cambrian of Oklahoma and Texas, and its biostratigraphic significance

TRILOBITES of the family Missisquoiidae Hupé 1955 occur throughout Laurentian North America in a relatively narrow interval of what is now the latest Cambrian succession (e.g., Shaw 1951; Winston & Nicholls 1967; Stitt 1971, 1977; Taylor & Halley 1974; Ludvigsen 1982; Fortey 1983; Westrop 1986; Dean 1989). Although widely distributed, both geographically and environmentally, missisquoiid trilobites have been assigned traditionally to a small number of species of Missisquoia Shaw 1951. However, Fortey (in Fortey et al. 1982) argued that Lunacrania Kobayashi 1955 was a valid genus (see Dean 1977 for an alternative interpretation), and later (1983) proposed that Missisquoia was a junior synonym of Parakoldinioidia Endo 1937. Fortey’s views prevailed, albeit slowly (e.g., Adrain in Jell & Adrain 2003; Westrop in Landing et al. 2011), and Lee et al. (2008) expanded the roster of Laurentian missisquoiid genera further by removing Tangshanaspis Zhou & Zhang 1978 from synonymy with Parakoldinioidia (see Ludvigsen 1982). Despite these revisions to the supraspecific systematics, the number of missisquoiid species reported from the Laurentian uppermost Cambrian strata remains low. Nowhere is this more obvious than in the classic succession of Oklahoma, which was collected in fine stratigraphic detail by Stitt (1971, 1977). Through an interval of 61 metres in the Joins Ranch section (JoR–1058—JoR–1257; Stitt 1971), Stitt viewed Missisquoiidae as represented by only two species, Tangshanaspis depressa (Stitt 1971) and Parakoldinioidia stitti Fortey 1983 (= Missisquoia typicalis of Stitt). The latter species has been recorded throughout Laurentia under the name, Missisquoia typicalis Shaw (e.g., Shaw 1951; Winston & Nicholls 1967; Stitt 1971, 1977; Taylor & Halley 1974; Fortey et al.,1982; Westrop 1986; Dean 1989). However, Lee et al. (2008) noted that this taxon likely represents more than one species, and were unable to code it for phylogenetic analysis. Westrop (in Landing et al. 2011) agreed with Lee et al., and restricted P. stitti to its variably deformed type material from Vermont (Shaw 1951). Westrop (2013) recently evaluated the record of Tangshanaspis in Laurentia and concluded that Stitt (1971) erroneously associated sclerites of two distinct species when he named Missisquoia depressa. Moreover, isolated pygidia suggested that there might be as many as four species of Tangshanaspis represented in the Signal Mountain Formation of Oklahoma. Here, we continue the revision of Laurentian Missisquoiidae from restudy of Stitt’s (1971, 1977) collections from Oklahoma, as well as type material from Texas and western Canada. Our results change the history of Laurentian missisquoiids from relative stasis to a significant radiation following the terminal Sunwaptan (base of Eurekia apopsis Zone) extinction interval. Parakoldinioidia is represented in Oklahoma and Texas by far more species than recognised previously, and this has significant biostratigraphic implications. Moreover, restudy of figured and associated material from collection CC–93 from the Wilberns Formation at Calf Creek, Texas WESTROP, S.R. & ADRAIN, J.M., 2014:04:25. The missisquoiid trilobite Parakoldinioidia Endo 1937 in the uppermost Cambrian of Oklahoma and Texas, and its biostratigraphic significance. Memoirs of the Association of Australasian Palaeontologists 45, 117-152. ISSN 0810-8889.