Bradoriida and Phosphatocopida (Arthropoda) from the Arthur Creek Formation (Middle Cambrian), Georgina Basin, central Australia

BRADORIIDS AND PHOSPHATOCOPIDS are small (<18 mm in length) bivalved arthropods, of Cambrian and early Ordovician in age, and have traditionally been assigned to ostracod crustaceans (Matthew 1886, 1896; Walcott 1905, 1913; Sylvester-Bradley 1961; Muller 1964, 1979). However, their biological position within the Arthropoda has long been, and still continues to be, an issue of contention (Jones & McKenzie 1980), largely because nothing was known of their soft anatomy. Over the last 25 years, this gap has been partly addressed by the discovery of three-dimensional soft parts in the Upper Cambrian of Sweden (phosphatocopids of the “Orsten” faunal assemblage; Muller 1979, 1982; Maas et al. 2003), the Middle Cambrian of Australia (Walossek et al. 1993), the Lower Cambrian of England (Siveter et al. 2001, 2003), and of essentially flattened soft parts in the Early Cambrian of China (Chengjiang Lagerstatte fauna; Hou et al. 1996; Shu et al. 1999 for the bradoriid Kunmingella Huo, 1956). Muller (1964, 1979) subdivided the order Bradoriida Raymond, 1935 into the suborders Phosphatocopina, which he considered to have primary phosphatic shells, and the Bradoriina, having supposed chitinous or calcareous shells. Both suborders were later raised to ordinal rank by Muller (1982). Kozur (1974), however, regarded the shell substance of the Phosphatocopina as secondarily phosphatised, and questioned the chemical basis of this subdivision. Although no comprehensive systematic study of the shell composition of the Bradoriida has been undertaken, it is now accepted (e.g. HinzSchallreuter 1993b; Siveter & Williams 1997; Siveter et al. 1996) that in the absence of soft part preservation, bradoriid and phosphatocopid taxonomy must be based on gross morphology, rather than compositional features of the shell. JONES, P.J. & LAURIE, J.R., 2006:07:29. Bradoriida and Phosphatocopida (Arthropoda) from the Arthur Creek Formation (Middle Cambrian), Georgina Basin, central Australia. Memoirs of the Association of Australasian Palaeontologists 32, 205-223. ISSN 0810-8889.