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The Palaeontology of the Lower Cambrian Emu Bay Shale


The Lower Cambrian Emu Bay Shale of Kangaroo Island, South Australia has long been famous as a source of magnificent specimens of the trilobites Redlichia takooensis and Hsuaspis bilobata. It is additionally important as the only site in Australia so far to yield a Burgess-Shale-type biota. As such it represents an important basis for comparison with other Burgess-Shale-type assemblages, particularly the Chenjiang Fauna in China, which is the closest palaeogeographically, although somewhat older. The depositional environment of the majority of Burgess-Shale-type assemblages is outer shelf, deeper water. The Emu Bay shale is unusual in that it appears to represent relatively shallow water deposition, confirming that soft tissue preservation took place in a range of environmental settings during the Cambrian. Most strikingly, however, some of the Emu Bay fossils display extensive mineralization of labile soft tissues. This is the oldest phosphatized muscle tissue and the first thus far reported from the Cambrian. Mineralized soft tissues are apparently rare among Burgess-Shale-type biotas. The type section of the Emu Bay Shale crops out on the east side of Emu Bay where it conformably overlies the White Point Conglomerate. Here it yields a rich assemblage of Hsuaspis, Redlichia, hyolithids, brachiopods, and the scleritome-bearing Chancelloria. At the Big Gully locality, its presumed correlative is unconformable on the White Point Conglomerate and yields soft-bodied fossils in addition to the trilobites, including the giant predator Anomalocaris, Isoxys, Tuzoia, the presumed worm Palaeoscolex, the problematic Myoscolex, and a number of rarer elements. The Big Gully trilobites rarely preserve any trace of non-biomineralized tissue; a small number of specimens of Redlichia have been reported with antennae. The Emu Bay Shale was considered late Early Cambrian in age but this was reassessed in the light of data on the Chinese Early Cambrian. The occurrence of R. takooensis and closely related species of Hsuaspis indicates an equivalence to the Tsanglangpuian in the Chinese sequence, and contemporary South Australian faunas correlate with the Botomian of Siberia. Thus the Emu Bay Shale is older than the Middle Cambrian Burgess Shale, but younger than the upper Atdabanian Chengjiang fauna of China.


The Fauna


The Arthropods

Anomalocaris

Trilobites

Isoxis

Myoscolex


Not The Arthropods

Wiwaxia

Palaeoscolex