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 Emu Bay Shale Konservat-Lagerstätte (Cambrian Series 2, Stage 4) on Kangaroo Island, South Australia, is the source of two new non-biomineralized artiopodan arthropods. 'Squamacula buckorum' n. sp. is the first record outside of China of a genus otherwise known only from its type species, 'S. clypeata', from the Chengjiang biota. The Australian species displays the long cephalic doublure and spiniform exopod setae that are apomorphic for this genus, provides new information on the alimentary tract and mid gut glands (the latter preserved as three-dimensional, permineralized structures), and indicates inter specific variability in trunk segment numbers. The distribution of 'Squamacula' strengthens the bio geographic connections between early Cambrian "Burgess Shale-type" biotas of Australia and South China. 'Australimicola spriggi' n. gen. nsp. represents a monotypic genus resolved in a cladistic analysis of Cambro-Ordovician artiopodans as most closely related to or within Conciliterga (a clade containing 'Helmetia', 'Kuamaia', 'Kwanyinaspis', 'Rhombicalvaria', 'Saperion', 'Skioldia', and 'Tegopelte'). Compared with other members of this clade from Chengjiang and the Burgess Shale, the new genus is diagnosed by an elongate trunk with 23 thoracic tergites having spatulate pleural tips and a small pygidium possessing a single, elongate pair of pleural spines, with specimens also showing a hypostome attached to an anterior (or prehypostomal) sclerite, antennae, short endopods, an annulated alimentary tract, and a series of three-dimensional, permineralized mid gut glands. An alternative relationship between 'Australimicola' and the Early Ordovician-Early Devonian Cheloniellida explains the shared anterior flexure of trunk pleurae but forces dubious homologies in other characters, such as dorsally-articulated furcae versus spines.

Despite the status of the eye as an "organ of extreme perfection", theory suggests that complex eyes can evolve very rapidly. The fossil record has, until now, been inadequate in providing insight into the early evolution of eyes during the initial radiation of many animal groups known as the Cambrian explosion. This is surprising because Cambrian Burgess-Shale-type deposits are replete with exquisitely preserved animals, especially arthropods, that possess eyes. However, with the exception of biomineralized trilobite eyes, virtually nothing is known about the details of their optical design. Here we report exceptionally preserved fossil eyes from the Early Cambrian (~515 million years ago) Emu Bay Shale of South Australia, revealing that some of the earliest arthropods possessed highly advanced compound eyes, each with over 3,000 large ommatidial lenses and a specialized 'bright zone'. These are the oldest non-biomineralized eyes known in such detail, with preservation quality exceeding that found in the Burgess Shale and Chengjiang deposits. Non-biomineralized eyes of similar complexity are otherwise unknown until about 85 million years later. The arrangement and size of the lenses indicate that these eyes belonged to an active predator that was capable of seeing in low light. The eyes are more complex than those known from contemporaneous trilobites and are as advanced as those of many living forms. They provide further evidence that the Cambrian explosion involved rapid innovation in fine-scale anatomy as well as gross morphology, and are consistent with the concept that the development of advanced vision helped to drive this great evolutionary event.

The Leanchoiliidae is well-known from abundant material of 'Leanchoilia', from the Burgess Shale and Chengjiang Konservat-Lagerstätten. The first Australian member of the group is 'Oestokerkus megacholix' gen. et sp. nov., described from the Emu Bay Shale (Cambrian Series 2, Stage 4), at Buck Quarry, Kangaroo Island, South Australia, and is intermediate in age between the well known leanchoiliid species from the Burgess Shale and Chengjiang. Phylogenetic analysis of "short great appendage" arthropods (Megacheira) in the context of the chelicerate stem group resolves the Australian species as sister to Burgess Shale, Utah, and Chengjiang 'Leanchoilia' species, but most readily distinguished from 'Leanchoilia' and 'Alalcomenaeus' by a different telson shape, interpreted as being forked, widening distally, and with a few dorsally curved spines at the posterior angle. Leanchoiliid interrelationships are stable to alternative character weights, and Megacheira corresponds to a clade in most analyses.

Early Cambrian tommotiids are problematic fossil metazoans with external organophosphatic sclerites that have been considered to be basal members of the lophophorate stem group. Tommotiids are almost exclusively known from isolated or rarely fused individual sclerites, which made previous reconstructions of the actual organism highly conjectural. However, the recent discovery of the first articulated specimens of the tommotiid 'Eccentrotheca' revealed a tubular sclerite arrangement (scleritome) that limited the possible life habit to sessile filter feeding and thus further supported a lophophorate affinity. Here, we report the first articulated specimens of a second tommotiid taxon, 'Paterimitra' from the Early Cambrian of the Arrowie Basin, South Australia. Articulated specimens of 'Paterimitra' are composed of two bilaterally symmetrical sclerite types and an unresolved number of small, asymmetrical and irregular crescent-shaped sclerites that attached to the anterior margin of the symmetrical sclerites. Together, the sclerites form an open cone in which the symmetrical sclerites are joined together and form a small posterior opening near the base of the scleritome, while the irregular crescent-shaped sclerites defined a broad anterior opening. The coniform scleritome of 'Paterimitra' is interpreted to have attached to hard substrates via a pedicle that emerged through the small posterior opening (sometimes forming a tube) and was probably a sessile filter feeder. The scleritome of 'Paterimitra' can be derived from the tubular scleritome of 'Eccentrotheca' by modification of basal sclerites and reduction in tube height, and probably represents a more derived member of the brachiopod stem group with the paired symmetrical sclerites possibly homologous to brachiopod valves.

The lower Cambrian Emu Bay Shale on Kangaroo Island, South Australia, contains the only known Cambrian Burgess Shale-type biota in Australia. Two new lamellipedian arthropods, 'Emucaris fava' gen. et sp. nov. and Kangacaris zhangi gen. et sp. nov., from the Emu Bay Shale Lagerstätte are described as monotypic genera that are resolved cladistically as a monophyletic group that is sister to Naraoiidae + Liwiidae and classified within the Nektaspida as a new family Emucarididae. Shared derived characters of Emucarididae involve a bipartite, elongate hypostome and elongation of the pygidium relative to the cephalic shield and very short thorax. A monophyletic Liwiidae is composed of 'Liwia' and the Ordovician 'Tariccoia' + 'Soomaspis' but excludes 'Buenaspis', and even the membership of 'Buenaspis' in Nektaspida is contradicted amongst the shortest cladograms. New morphological interpretations favour affinities of 'Kwanyinaspis' with Conciliterga rather than with Aglaspidida, and 'Phytophilaspis' with Petalopleura.

Mode of preservation and method of recovery strongly influences our understanding of the life habits of extinct organisms. Bradoriid arthropods were abundant, and diverse members of early Cambrian ecosystems and most life reconstructions display these animals with the two shields of the carapace open in a 'butterfly' configuration. This favoured reconstruction is largely based on the abundance of 'crack-out' specimens preserved in this position (e.g. 'Kunmingella' from the early Cambrian of China). In contrast, large collections of acid processed bradoriids from the Arrowie Basin of South Australia (Cambrian Stage 3) are preserved with a narrow gape at the ventral margin or completely closed with the carapace folded along the dorsal midline. The relative abundance of conjoined, closed (or partially closed) specimens from the lower Cambrian Hawker Group succession suggests that at least some bradoriid taxa were capable of withdrawing appendages and tightly closing the shields, challenging the common view that the majority of bradoriids usually held their carapaces open in a 'butterfly' configuration during life. New data show that layers of the bradoriid carapace are continuous through the dorsal fold with no evidence for complex articulating structures as in ostracod hinges. The relatively pliable, sclerotized or lightly mineralized calcium phosphate composition of the carapace and the simple, flexible dorsal fold facilitated opening and closing of the shields. Despite not being closely related, ostracods share close biomechanical and ecological similarities with bradoriids. The evolution of more complex articulating hinge structures - together with well-developed musculature - in ostracods during the Early Ordovician, may have provided more efficient means for shield articulation and movement, thus promoting the ecological success of ostracods throughout the Phanerozoic.

Shells of 'Oikozetetes' and isolated halkieriid sclerites from a section of the lower Cambrian Mernmerna Formation in the Flinders Ranges, South Australia, are tentatively considered as being derived from the same scleritome. Details of shell morphology and the possible combination of biomineralized shell and sclerites suggest that 'Oikozetetes', if interpreted correctly, is closely related to 'Halkieria'. A new interpretation of 'Oikozetetes' shell morphology, in addition to the first report of paired muscle scars on the interior surface, sheds new light on the possible functional morphology of halkieriid shells and the means of attaching the shell to the body. The occurrence of 'Oikozetetes' in South Australia extends its biostratigraphic range to the lower Cambrian and biogeographic range to East Gondwana.

A distinctive group of lobopodians known from Cambrian Stage 5 in western Laurentia includes 'Acinocricus' Conway Morris & Robison, 1988, from the Spence Shale in Utah, and an unnamed species from the Burgess Shale, British Columbia, popularly known as 'Collins' monster'. The temporal gap from their closest relative, the Chengjiang lobopodian 'Luolishania', is bridged by a single, incomplete specimen of a Collins' monster-type lobopodian from the Emu Bay Shale (Cambrian Series 2, Stage 4), Kangaroo Island, South Australia, the first lobopodian discovered in this Konservat-Lagerstätte. Pending formal description of the Burgess Shale species, the Australian specimen is left unassigned to a genus.

The tommotiid 'Camenella reticulosa' is redescribed based on new collections of well preserved sclerites from the Arrowie Basin (Flinders Ranges), South Australia, revealing new information concerning morphology and micro-structure. The acutely pyramidal mitral sclerite is described for the first time and the sellate sclerite is shown to be coiled through up to 1.5 whorls. Based on 'Camenella', a model is proposed by which tommotiid sclerites are composed of alternating dense phosphatic, and presumably originally organic-rich, laminae. 'Camenella' is morphologically most similar to 'Lapworthella', 'Kennardia', and 'Dailyatia', and these taxa are interpreted to represent a monophyletic clade, here termed the "camenellans", within the Tommotiida. Potential reconstructions of the scleritome of Camenella are discussed and although a tubular scleritome construction was recently demonstrated for the tommotiids Eccentrotheca and Paterimitra, a bilaterally symmetrical scleritome model with the sclerites arranged symmetrically on the dorsal surface of a vagrant animal can not be ruled out.