Trilobites of the Emu Bay Shale, Australia
last revised 01 July 2007 by S.M. Gon III
Locality: Kangaroo Island, Emu Bay & Cape D'Estaing, South Australia
Stratigraphy: Emu Bay Shale Formation
Age: Lower Cambrian. ca 525 mya
 
North Coast of Kangaroo Island, Emu Bay (photo courtesy David Simpson)

The Emu Bay Shale Formation of Kangaroo Island, South Australia is Australia's only known Burgess-Shale-type Konservat-Lagerstätte, and includes faunal elements such as Anomalocaris, Tuzoia, Isoxys, Xandarella, and Primicaris, in common with other Burgess-Shale-type assemblages, particularly the Chengjiang Fauna in China, the closest palaeogeographically, although somewhat older. The site is also the source of magnificent specimens of trilobites such as Redlichia takooensis, Emuella polymera, Balcoracania dailyi, and Estaingia (=Hsuaspis) bilobata. Balcoracania and Emuella are members of the distinctive redlichiine superfamily Emuelloidea, known for numerous segments (over 60 in large Balcoracania specimens), and so far entirely restricted to Australia.

The depositional environment of the majority of Burgess-Shale-type assemblages is outer shelf, deeper water. The Emu Bay shale in contrast, appears to represent relatively shallow water deposition, indicating that soft tissue preservation occurred in a range of environmental settings during the Cambrian. Some Emu Bay fossils display extensive mineralization of soft tissues, most often of blocky apatite or fibrous calcium carbonate, but some including 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 (8 km east of White Point), 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.
   
  
Location of the Emu Bay Shale lagerstatte today
 Locality of Emu Bay Shale during the Early Cambrian

The Emu Bay Shale was initially considered late Early Cambrian in age, but this was calibrated by data on the Early Cambrian in China. Occurrence of R. takooensis and species of Hsuaspis matches the Tsanglangpuian in the Chinese sequence, and contemporary South Australian faunas correlate with the Botomian of Siberia. So the age of the Emu Bay Shale lies between the Middle Cambrian Burgess Shale, and the upper Atdabanian Chengjiang of China. Below are four representative species from the Emu Bay Shale Formation:

   
   
 
  
Balcoracania dailyi
(Pocock 1970)
ORDER REDLICHIIDA
Family Emuellidae
 Redlichiida takooensis
Lu 1950
ORDER REDLICHIIDA
Family Redlichiidae
 Holyoakia simpsoni
Paterson & Jago 2006
ORDER CORYNEXOCHIDA
Family Dorypygidae
 Estaingia bilobata
(Pocock 1964)
ORDER PTYCHOPARIIDA
Family Estaingiidae
Some trilobite specimens from Emu Bay have their soft parts preserved, as in the Burgess Shale and Chengjiang lagerstatten. Redlichia takooensis with antennae and limbs apparent are the most well-known of these. In addition to trilobites, there were other species of arachnomorph (trilobite-like clade) arthropods such as Xandarella, and Primicaris. These trilobite-like arthropods demonstrate that the group from which trilobites arose was itself successful and diverse, though being uncalcified, are only preserved at exceptional lagerstatten such as the Burgess Shale and Chengjiang. Because the Burgess Shale was the first lagerstatte with such exceptional preservation, other sites with similar preservation are referred to as "Burgess Shale type" lagerstatten.
TRILOBITA OF THE EMU BAY SHALE

Order Redlichiida
Suborder Redlichiina
Superfamily Emuelloidea
Family Emuellidae
Balcoracania dailyi Pocock 1970
Balcoracania flindersi Pocock 1970*
Emuella polymera Pocock 1970
Emuella dalgarnoi Pocock 1970
Family Megapharanaspidae
Megapharanaspis nedini Paterson & Jago 2006

Superfamily Redlichioidea
Family Redlichiidae
Redlichia takooensis Pocock 1964

Order Ptychopariida
Suborder Ptychopariina
Superfamily Ellipsocephaloidea
Family Estaingiidae
Estaingia bilobata Pocock 1964

Order Corynexochida
Suborder Corynexochina
Family Dorypygidae
Holyoakia simpsoni Paterson & Jago 2006

*In Paterson & Edgecombe 2006, Balcoracania flindersi is regarded as a synonym for B. dailyi, while both species of Emuella are maintained. 
Some Emu Bay Shale literature:

Hagadorn, J.W. 2002. Burgess Shale-type Localities: The global picture. in: Bottjer, D.J., W. Etter, J.W. Hagadorn & C.M. Tang, eds., Exceptional Fossil Preservation -- A Unique View on the Evolution of Marine Life. 403 pp. Columbia University Press.

Nedin, C., 1995. The Emu Bay Shale, a Lower Cambrian fossil Lagerstätte, Kangaroo Island, South Australia. Memoirs of the Association of Australasian Palaeontologists, 18, 31-40.

Paterson, J.R. & G.D., Edgecombe. 2006. The Early Cambrian trilobite family Emuellidae Pocock, 1970: Systematic position and revision of Australian species. Journal of Paleontology 80(3): 496-513.

Paterson, J.R. & J.B. Jago. 2006. New trilobites from the Lower Cambrian Emu Bay Shale Lagerstätte at Big Gully, Kangaroo Island, South Australia. Memoirs of the Association of Australasian Palaeontologists 32: 43-57.

Trilobites of South Australia, a website by Dave Simpson

Australian Trilobites: A Species List and Bibliography by Greg Edgecombe and the Australian Museum

Related trilobite localities: Chengjiang, China, Burgess Shale, Canada
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Walking Trilobite animation ©2000 by S. M. Gon III