Abstract
Abstract. Some 40 bradoriid and phosphatocopid (Arthropoda) species are known from the Cambrian of the former Soviet Union. The faunas occur chiefly in Asia (mostly Siberia and Kazakhstan; also Kirghizia); west of the Urals bradoriid and phosphatocopid faunas are sparse, occurring in the Leningrad region, Belarus and Estonia. Most specimens are recovered as crack-out material from clastic and impure carbonate rocks; acid resistant valves from limestones are a minor component of the known faunas.Early Cambrian (Atdabanian-Botomian) faunas are widespread; middle and late Cambrian faunas are scarcer and are known largely from Siberia and Kazakhstan. Though many species are seemingly short-ranging, currently most have only local biostratigraphic significance, with only a few having practical international correlative value.Palaeogeographically, faunas west of the Urals show affinites with those of the Early Palaeozoic Baltica and Avalonia palaeocontinents (Olenellid trilobite realm). Siberian and central Asian (Kazakhstan, Kirghizia, Gorny–Altay–Mongolian belt) faunas show clear affinities with those of palaeocontinental South China and eastern Gondwana (Redlichiid trilobite realm).
Highlights
Bradoriids and phosphatocopids are small, bivalved, almost exclusively Cambrian arthropods which first appear coevally with, or slightly later than the first trilobites
Several recent studies have highlighted their widespread occurrence in the Cambrian of especially Britain, North America, Australia (Jones & McKenzie, 1980; Hinz-Schallreuter, 1993a), the Baltic (Hinz-Schallreuter, 1993b, 1993c) and China and have demonstrated their biogeographical and regional and international correlative potential (e.g. Siveter et al, 1993; Williams et al, 1994b; Siveter & Williams, 1995)
Bradoriids and phosphatocopids are known from several parts of the former Soviet Union but a comprehensive account of their geographical occurrence and their biostratigraphic and biogeographic distribution and value remains to be elucidated; these are the primary aims of our paper
Summary
Bradoriids and phosphatocopids are small, bivalved, almost exclusively Cambrian arthropods which first appear coevally with, or slightly later than the first trilobites (see Siveter et af., 1996 and references therein). HISTORY OF RESEARCH AND GEOGRAPHICAL DISTRIBUTION The earliest documentation of bradoriids and phosphatocopids are based on mid- to late 19th Century studies of British and North American faunas (see Rushton et al, in press; Siveter & Williams, 1997; Williams & Siveter, in press) These groups were only quite recently recorded from the former Soviet Union, as a result of field and faunal studies in the Cambrian of Asia (Figs 1, 2). Most recent studies have either been short general summaries about the bradoriids and phosphatocopids of the former Soviet Union (Melnikova, 199Oc, 1990d) or detailed revisions of Siberian species which, in some cases, identify widespread biostratigraphical potential (e.g. Siveter et al, 1993, 1994, 1996; Hinz-Schallreuter, 1993~W; illiams et al, 1994a).The possibility of obtaining additional bradoriid and phosphatocopid material from the former Soviet Union is well demonstrated by the acid-resistant faunas obtained from limestones in Siberia (Miiller et al, 1995) and from Kazakhstan during the 1980s by Melnikova and Taylor
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