The Emu Bay Shale Konservat-Lagersattte: a view of Cambrian life from East Gondwana
Recent fossil discoveries from the lower Cambrian Emu Bay Shale (EBS) on Kangaroo Island, South Australia, have provided critical insights into the tempo of the Cambrian explosion of animals, such as the origin and seemingly rapid evolution of arthropod compound eyes, as well as extending the geographical ranges of several groups to the East Gondwanan margin, supporting close faunal affinities with South China. The EBS also holds great potential for broadening knowledge on taphonomic pathways involved in the exceptional preservation of fossils in Cambrian Konservat-Lagerstätten. EBS fossils display a range of taphonomic modes for a variety of soft tissues, especially phosphatization and pyritization, in some cases recording a level of anatomical detail that is absent from most Cambrian Konservat-Lagerstätten.
New trilobites from the Lower Cambrian Emu Bay Shale Lagerstätte at Big Gully, Kangaroo Island, South Australia
Two new trilobites from the Lower Cambrian Emu Bay Shale Lagerstätte at Big Gully, Kangaroo Island, are described. 'Megapharanaspis nedini' gen. et sp. nov. is placed in the Megapharanaspidae, a new family of the Emuelloidea. 'Holyoakia simpsoni' sp. nov. represents the first occurrence of the genus outside Antarctica, providing further confirmation of the close faunal affinity between Cambrian trilobite faunas from Australia and East Antarctica. New specimens of 'Redlichia takooensis' are documented that provide new morphological information, including a description of the rostral plate and hypostome.
Biodiversity, biofacies and biogeography of middle Cambrian (Series 3) arthropods (Trilobita and Agnostida) on the East Gondwana margin
Cambrian (Series 3) trilobites and agnostids from the palaeoequatorial East Gondwana margin, comprising mainland Australia, Tasmania, New Zealand and eastern Antarctica. Analysis of 224 genera of trilobites and agnostids from 78 fossil sites across three Cambrian Stage 3 time intervals (Stage 5, Drumian, Guzhangian) is presented. Results of the Stage 5 analyses reveal a major grouping of faunas from the Arafura, Georgina and Warburton basins, plus the Gnalta Shelf in New South Wales, typically represented by deep-water, outer shelf assemblages that commonly contain agnostids, oryctocephalids, 'Pagetia' and 'Xystridura'. Faunal exchange between these depocentres was permitted by a transgression that was associated with tectonically induced subsidence of basement blocks in the Georgina Basin, such as the Mt Isa block, during this stage. Drumian faunas are represented by three distinct site groupings: Group D1 is represented exclusively by several Georgina Basin assemblages that occur in shallow marine (intertidal to subtidal) settings, including the common trilobite genera 'Asthenopsis', 'Chondranomocare', 'Fuchouia' and 'Penarosa', plus a range of agnostids, that inhabited an epeiric sea with connections totheopenocean; Groups D2 and D3 are represented by sites along the entire margin, from northern Australia to the Transantarctic Mountains that characterise a range of shallow to deep marine palaeoenvironments. These complex Drumian groupings most likely reflect long-range faunal exchange along the margin permitted by the eustatic transgression taking place at this time, which particularly influenced the distribution of eurytopic agnostid species that are common in these faunas. Two Drumian faunas from the Hodge Slate and Que River Beds in Tasmania (part of Group D3) exemplify a unique biofacies occurring in a deep-water, outer shelf setting, possibly in the lower photic zone, with the former assemblage containing the blind trilobites 'Meneviella' and 'Holocephalina', and the latter containing only agnostids. Results of the Guzhangian analyses show four obvious faunal groupings, with Groups G1 and G2 being the largest and representing sites along the entiremargin, while Group G3 is restricted to some of the Warburton Basin, Tasmanian and Antarctic sites, and Group G4 comprises only Tasmanian sites. Groups G1 and G2 correspond to Boomerangian and Mindyallan faunas, respectively, representing two temporally separated biofacies situated on the outer shelf to slope: Group G1 assemblages typically contain the trilobites 'Acontheus', 'Amphoton', 'Centropleura', 'Dorypyge', 'Fuchouia', 'Huzhuia', 'Pianaspis' and 'Solenoparia'; and Group G2 faunas often contain the trilobites 'Blackwelderia', 'Genevievella','Liostracina', 'Meteoraspis', 'Metopotropis', 'Mindycrusta', 'Palaeadotes', 'Rhyssometopus' and 'Townleyella'; with both groups containing a considerable number of eurytopic agnostid species. Group G4 assemblages also inhabit outer shelf settings, but have lower diversity, with common taxa including the trilobite Nepea and the agnostids 'Clavagnostus', 'Oidalagnostus' and 'Valenagnostus'. The considerable number of cosmopolitan Guzhangian agnostid species in association with distinct deep-water trilobite-agnostid assemblages along the entire East Gondwana margin strongly reflects the eustatic transgressive event that reached its pinnacle during this stage of Cambrian Series 3 that allowed for greater faunal exchange between areas on the margin and other palaeocontinents and terranes. The East Gondwana margin represents a biodiversity "hot spot" during Cambrian Series 3, containing almost one-quarter (~23%) of the trilobite and agnostid genera known worldwide. Our data support previous interpretations that Cambrian Series 3 trilobites and agnostid faunas from the East Gondwana margin, particularly those from Australia and Antarctica, have strong biogeographic links with those from Chinese terranes (especially North and South China), the Himalaya, and to a lesser extent, Iran, Kazakhstan, Laurentia and Siberia. Our data also reveal an overall increase in generic diversity throughout Cambrian Series 3, reaching a peak in the Guzhangian, with major diversifications most likely corresponding to eustatic transgressive phases, particularly in the Drumian and Guzhangian. This diversity trend for the East Gondwanamargin closely matches that observed for contemporaneous faunas in other parts of the world, especially in China, Kazakhstan and West Gondwana, although diversity in the latter region reaches an acme in Drumian times.
Revision of 'Discomesites' and 'Estaingia' (Trilobita) from the Lower Cambrian Cymbric Vale Formation, Western New South Wales: Taxonomic, Biostratigraphic and Biogeographic Implications
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.
First report of the early Cambrian stem group brachiopod 'Mickwitzia' from East Gondwana
The first mickwitziid brachiopod, 'Mickwitzia' sp., from East Gondwana is described from the lower Cambrian Ajax Limestone, Mt Scott Range in South Australia. The shells are fragmentary, but preserve sufficient details of morphology and micro-structure to allow positive identification to genus. The morphology of the dorsal valve apex and the extended cones on the internal surface indicate a close affinity with 'Mickwitzia muralensis' Walcott, 1913 from the early Cambrian of British Columbia, but scarcity of material precludes detailed comparison. This find extends the known range of the pivotal stem group brachiopod 'Mickwitzia' to East Gondwana.
Global Cambrian trilobite palaeobiogeography assessed using parsimony analysis of endemicity
Palaeobiogeographical data on Cambrian trilobites obtained during the twentieth century are combined in this paper to evaluate palaeoceanographic links through 'c'. 30 myr, once these arthropods biomineralized. Worldwide major tectonostratigraphic units are characterized at series intervals of Cambrian time and datasets of trilobite genera (629 for Cambrian Series 2, 965 for Cambrian Series 3, and 866 for the Furongian Series) are analysed using parsimony analysis of endemicity. Special attention is given to the biogeographical observations made in microcontinents and exotic terranes. The same is done for platform-basinal transects of well-known continental margins. The parsimony analysis of endemicity analysis resulted in distinct palaeogeographical area groupings among the tectonostratigraphic units. With these groupings, several palaeobiogeographical units are distinguished, which do not necessarily fit the previously proposed biogeographical realms and provinces. Their development and spatial distributions are broadly controlled by Cambrian palaeoclimates, palaeogeographical conditions (e.g. carbonate productivity and anoxic conditions) and ocean current circulation.
Palaeobiogeography of the Ordovician trilobite 'Prosopiscus', with a new species from western New South Wales
'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.
The 'great appendage' arthropod 'Tanglangia': Biogeographic connections between early Cambrian biotas of Australia and South China
The Cambrian 'great appendage' arthropod 'Tanglangia' Luo and Hu in Luo et al., 1999, has until now been known from a single species from the Chengjiang biota of southwest China (Cambrian Series 2, Stage 3). A new species from the Emu Bay Shale Konservat-Lagerstätte on Kangaroo Island, South Australia (Cambrian Series 2, Stage 4), 'Tanglangia rangatanga' sp. nov., extends the geographic and stratigraphic ranges of this genus and amplifies the biogeographic links between non-biomineralised faunas from the early Cambrian of Australian East Gondwana and the South China Plate.
Cambrian palaeoscolecids (Cycloneuralia) from Gondwana and reappraisal of species assigned to 'Palaeoscolex'
The discovery of new palaeoscolecid material (Cycloneuralia) from the Emu Bay Shale Konservat-Lagerstätte of Kangaroo Island, South Australia (Cambrian Series 2, Stage 4) and from the Murero biota of NE Spain (Cambrian Series 3, Stage 5-Drumian) has prompted a reappraisal of 'Palaeoscolex' Whittard, 1953, the genus to which species from these, and other Cambrian localities, have most recently been assigned. Available data from scanning electron microscopy show the presence of 'Hadimopanella'-type sclerites covering the surface of these taxa, permitting taxonomic schemes based on microfossils and whole-body compression fossils to be reconciled. The sclerite pattern, size and shape indicate that several of the Cambrian species assigned to 'Palaeoscolex' need to be reassigned to 'Wronascolex' Ivantsov and Zhuravlev, 2005, a genus originally described from Siberia. The studied material includes 'Wronascolex antiquus' ( Glaessner, 1979) and 'Wronascolex iacoborum sp'. nov. from Kangaroo Island (Australia) and two new specimens of 'Wronascolex'? from the Iberian Ranges (Spain). SEM examination of the types of 'Palaeoscolex ratcliffei' Robison, 1969, a Cambrian species from Utah to which Murero material has been compared, suggests that this species should possibly be assigned to 'Wronascolex'. These taxa are also considered in a Cambrian palaeobiogeographic context, together with the presence of isolated Hadimopanella sclerites, showing a distribution of Wronascolex largely confined to palaeotropical environments.