The family Emuellidae Pocock, 1970 was established for Emuella Pocock, 1970 and Balcoracania Pocock, 1970 from the Lower Cambrian of South Australia. Based on their peculiar trunk tagmosis, emuellids have been interpreted as the sister group of all other trilobites with dorsal facial sutures, and classified as high as the ordinal level. Cladistic analysis with a range of exemplar taxa of the Olenellina and Redlichiina instead resolves the emuellids within the Redlichiina, with tagmosis into a prothorax and opisthothorax ("telosoma") nonhomologous in olenellines and emuellids. A taxonomic revision of Australian species identifies Balcoracania flindersi as a junior subjective synonym of B. dailyi, whereas the two named species of Emuella are considered to be distinct. Balcoracania dailyi possesses up to 103 thoracic segments, the maximum number recorded in any trilobite

The taxonomy of Discomesites and Estaingia from the Lower Cambrian Cymbric Vale Formation of western New South Wales is revised. Discomesites is regarded as a valid subgenus of Pagetides. Pagetides (Discomesites) fragum is considered a senior subjective synonym of P. (D.) lunatulus. Pagetides (Discomesites) spinosus from the Shackleton Limestone in the Holyoake Range, Transantarctic Mountains, is considered to be a junior subjective synonym of P. (D.) fragum. Estaingia cerastes from the Cymbric Vale Formation is considered to be synonymous with Hsuaspis cf. H. bilobata from the Shackleton Limestone. The Cymbric Vale Formation trilobite fauna is of late Early Cambrian (late Botoman) age, equivalent to the Pararaia janeae Zone of South Australia, based on correlation of the Syringocnema favus archaeocyathan fauna. Absolute ages of recently dated tuffs from the Cymbric Vale and Billy Creek Formations are questioned, based on new information regarding the stratigraphic position of the Cymbric Vale Formation tuff in relation to archaeocyathan and trilobite biostratigraphy. The co-occurrence of Pagetides (Discomesites) fragum and Estaingia cerastes in the upper part of the Cymbric Vale Formation and in the Shackleton Limestone represents the first species-level correlation between the Lower Cambrian of Australia and Antarctica using trilobites. The distribution of these trilobite species, in association with the Syringocnema favus archaeocyathan fauna, provides supporting evidence that Australia and Antarctica were connected by a continuous carbonate-detrital shelf during the late Early Cambrian (mid-late Botoman),allowing faunal exchange between these regions.

Cambrian rocks in South Australia occur in the Stansbury, Arrowie, eastern Officer and Warburton Basins. The succession in the Stansbury and Arrowie Basins can be divided into three sequence sets (supersequences), C1, C2 and C3. Sequence set C1 can be divided into five third-order sequences: C1.0, C1.1A, C1.1B, C1.2 and C1.3. Trilobites from the Stansbury and Arrowie Basins are restricted largely to the lower part of the succession. Four trilobite zones are recognized: 'Abadiella huoi' (latest Atdabanian–earliest Botoman), 'Pararaia tatei', 'Pararaia bunyerooensis' and 'Pararaia janeae' Zones (all Botoman). Trilobites higher in the succession are known from only a few horizons and in part correlate with the upper Lower Cambrian Lungwangmiaoan Stage of China, equivalent to the top Toyonian. 'Pagetia sp.' has been reported in the Coobowie Formation of the Stansbury Basin, thus suggesting an early Middle Cambrian age. The Cambrian faunas of the Warburton Basin range in age from early Middle Cambrian (Late Templetonian) to very Late Cambrian, although the richest faunal assemblages are late Middle Cambrian ('Ptychagnostus punctuosus to Goniagnostus nathorsti' Zones). Conodonts, including 'Cordylodus proavus', occur in a Datsonian fauna. The Arrowie Basin contains the most complete and best studied archaeocyath succession in the Australia–Antarctica region. The 'Warriootacyathus wilkawillensis', 'Spirillicyathus tenuis' and 'Jugalicyathus tardus' Zones from the lower Wilkawillina Limestone (Arrowie Basin) and equivalents are correlated with the Atdabanian. Botoman archaeocyathids occur higher in the Wilkawillina Limestone. The youngest (Toyonian) archaeocyath fauna in Australia occurs in the Wirrealpa Limestone (Arrowie Basin). Brachiopods and molluscs of the Arrowie and Stansbury Basins can be divided into four biostratigraphic assemblages. Several informal Early Cambrian SSF biostratigraphic assemblages are recognized. Probable tabulate-like corals occur in the Botoman Moorowie Formation. Seven informal acritarch assemblages occur in the Early Cambrian of the Stansbury and Arrowie Basins. Trace fossils may mark the Precambrian–Cambrian boundary. Only two of several tuffaceous horizons from the Stansbury and Arrowie Basins have been dated (i) a date of 522.0 ± 2.1 Ma from the Heatherdale Shale of the Stansbury Basin, about 400m above latest Atdabanian archaeocyathids and (ii) a date of 522.0 ± 1.8 Ma from the lower part of the Billy Creek Formation in the Arrowie Basin. Neither date is regarded as reliable.

An assemblage of bradoriid arthropods from the Mernmerna Formation in the Donkey Bore Syncline, central Flinders Ranges, South Australia contains eleven species, including three species of the enigmatic ornamented spine 'Mongolitubulus'. Four new taxa are described, 'Onagrocharion tuberosus' gen. et sp. nov., 'Amphikeropsis myklosis' gen. et sp. nov., 'Hipponicharion australis' sp. nov. and 'Mongolitubulus unispinosa' sp. nov. The presence of 'Hipponicharion australis' sp. nov. in the upper Mernmerna Formation represents the first occurence of the genus in Australia and extends the biogeographic range of Hipponicharion to eastern Gondwana. Bradoriid specimens of 'Mongolitubulus unispinosa' sp. nov. exhibiting a single mature ornamented spine attached to the central portion of the carapace provides definitive evidence of a bradoriid affinity for the enigmatic, widespread 'Mongolitubulus' small shelly fossil taxon. The assemblage includes several species that facilitate correlation with the Stansbury Basin of South Australia, but also with faunas from other Cambrian palaeocontinents, including Antarctica and Laurentia.

Monospecific assemblages of the trilobite 'Balcoracania dailyi' occur in lower Cambrian strata within the Adelaide Geosyncline in South Australia. Biostratinomic data from single bedding plane assemblages within the Warragee and Coads Hill Members of the Billy Creek Formation and White Point Conglomerate reveal a range of taphonomic signatures from census to within-habitat, time-averaged assemblages. These assemblages are interpreted as having inhabited protected, shallow, marginal marine environments. Size–frequency distributions, coupled with taphonomic data, show that the Warragee Member census assemblage represents a living population in a physically stressful environment within a tidally-influenced lagoon, while the original population structure of the Coads Hill Member and White Point Conglomerate assemblages has been lost due to varying degrees of taphonomic overprinting. Integration of taphonomic, stratigraphic and sedimentological data supports the interpretation of 'B. dailyi' as representing an opportunistic species. A preserved body cluster from the Warragee Member assemblage is considered to characterise a congregation formed for the purpose of synchronous reproduction and ecdysis, representing one of the oldest examples of gregarious behaviour in the arthropod fossil record. Furthermore, by analogy with modern horseshoe crabs, the high number of juveniles (i.e., protaspides and early meraspides) within the same assemblage are believed to be constituents of a nursery within the intertidal zone, with adults migrating into the shallows to copulate and spawn. Preserved moult ensembles from the Coads Hill Member and White Point Conglomerate have enabled the description of exuviation techniques for 'B. dailyi'.

The Memoirs series publishes peer reviewed papers on all aspects of palaeontology and its applications in the earth and biological sciences, including taxonomy, biostratigraphy, vertebrate and invertebrate palaontology, palaeoichnology, palaeobotany, palynology, palaeobiology, palaeoecology, palaeobiogeography and biogeochemistry among others. The Memoir series is designed for longer monographic treatments, but will also consider thematic sets of papers and commonly publishes conference proceedings.

Taxonomy of the Cambrian trilobite family Nepeidae is revised. Morphometric analyses of the genera 'Nepea' and 'Penarosa' demonstrate that use of proportions of linear dimensions of the cranidium to differentiate species is invalid, and that infrageneric variation is continuous. The taxonomy and biostratigraphy of all Australian species of Nepeidae is revised. Species considered valid herein include: 'Nepea narinosa' (type species), 'N. tonsillata', 'N. nans', 'Penarosa retifera' (type species), 'P. elaticeps', 'P. rhinodelphis', 'P. netenta', 'Loxonepea loxophrys' (type species) and Ferenepea hispida (type species). Folliceps is considered to be a junior subjective synonym of 'Nepea', 'Trinepea' is regarded as a junior subjective synonym of 'Penarosa', and Ascionepea is considered to be a junior subjective synonym of Ferenepea.

Abundant material from a new quarry excavated in the lower Cambrian Emu Bay Shale (Kangaroo Island, South Australia) and, particularly, the preservation of softbodied features previously unknown from this Burgess Shaletype locality, permit the revision of two bivalved arthropod taxa described in the late 1970s, 'Isoxys communis' and 'Tuzoia australis'. The collections have also produced fossils belonging to two new species: 'Isoxys glaessneri' and 'Tuzoia sp.' Among the soft parts preserved in these taxa are stalked eyes, digestive structures and cephalic and trunk appendages, rivalling in quality and quantity those described from better-known Lagerstätten, notably the lower Cambrian Chengjiang fauna of China and the middle Cambrian Burgess Shale of Canada.

Two new late Early Ordovician orthide brachiopods, 'Celsiorthis bulancis' n.gen. and n.sp. and Alocorthis psygmatelos n.gen. and n.sp., are described from the Tabita and Pingbilly formations at Mount Arrowsmith, northwestern New South Wales. The associated conodont assemblage from the succession at Mount Arrowsmith indicates a late Bendigonian to Chewtonian age for the brachiopod bearing horizons.

'Prosopiscus' is particularly important in Ordovician palaeobiogeography because of its wide geographic distribution in Gondwana and peri-Gondwanan regions. It appears to have been confined to low palaeolatitudes, representing a characteristic member of the warm water eastern Gondwanan shelf faunas. Trends in the distribution of the Ordovician genus can be observed due to its long stratigraphic range. 'Prosopiscus' was restricted to, and may have originated in, Australia during the late Early Ordovician (Bendigonian-Chewtonian). By the Middle Ordovician (Darriwilian), 'Prosopiscus' had dispersed to other parts of Gondwana and peri-Gondwana, including the North and South China blocks, Tarim, central Himalayas, and the Argentine Precordillera (South America). Possible explanations for the distribution of 'Prosopiscus' are that: (1) there were no oceanic barriers preventing dispersal of trilobites between different regions of Gondwana, thus permitting uninhibited migration over vast distances; (2) 'Prosopiscus' was not restricted to a specific biofacies; (3) a major eustatic transgression during the early Darriwilian may have facilitated the dispersal of 'Prosopiscus' in allowing further development and expansion of marine environments; and (4) a prolonged planktonic larval stage may have permitted wide dispersal.