Emu Bay Shale
|Emu Bay Shale
Stratigraphic range: Cambrian Stage 4 ("Lower Cambrian")
North Coast of Kangaroo Island, Emu Bay
© David Simpson
|Region||The north coast of Kangaroo Island, around Emu Bay and Cape D'Estaing|
|Country||South Australia, Australia.|
The Emu Bay Shale is a geological formation in Emu Bay, South Australia, containing a major Konservat-Lagerstätten (fossil beds with soft tissue preservation). It is one of two in the world containing Redlichiidan trilobites. The Australian's Emu Bay Shale correlated with upper Botomian Stage of the Lower Cambrian.
The Emu Bay Shale 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, Megapharanaspis nedini and Estaingia (=Hsuaspis) bilobata. Balcoracania and Emuella are the only known genera of the distinctive Redlichiina family Emuellidae, known for numerous thorax segments (a record of 103 in one large Balcoracania specimen), 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, including the oldest phosphatized muscle tissue – 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.
In 2011, six fossils of compound eyes dated to the Cambrian period (515 million years ago) were recovered from an excavation at Emu Bay on the Island. The eyes were the first ever found that belonged to Anomalocaris, proving that Anomalocaris was indeed closely related to arthropods as had been suspected. The find also indicated that advanced arthropod eyes had evolved very early, before the evolution of jointed legs or hardened exoskeletons. The eyes were 30 times more powerful than those of Trilobites, long thought to have had the most advanced eyes of any species contemporary with Anomalocaris and which were only able to sense night or day. With 16,000 lenses, the resolution of the 3 centimetres (1.2 in) wide eyes would have been rivalled only by that of the modern Dragonfly, which has 28,000 lenses in each eye.
NOTE: Much of the text of this article was used with permission of Sam Gon III from his below referenced web site, in particular from the Emu Bay page
- García-Bellido, D. C.; Paterson, J. R.; Edgecombe, G. D. (2013). "Cambrian palaeoscolecids (Cycloneuralia) from Gondwana and reappraisal of species assigned to Palaeoscolex". Gondwana Research. doi:10.1016/j.gr.2012.12.002.
- J. B. Jago, Xiaowen Sun and Wen-long Zang (December 2002). "Correlation within early Palaeozoic basins of eastern South Australia". pp. 1–22. Retrieved 2010-04-04.
- Glaessner, M. F. (1979). "Lower Cambrian Crustacea and annelid worms from Kangaroo Island, South Australia". Alcheringa: an Australasian Journal of Palaeontology (Taylor & Francis) 3 (1): 21–31. doi:10.1080/03115517908565437
- Popock, K. J. (1970). "The Emuellidae, a new family of trilobites from the Lower Cambrian of South Australia". Palaeontology 13: 522–562.
- Brett Williamson (30 June 2011). "Ancient discovery puts world's scientific eyes on Kangaroo Island". ABC News (Australia).
- Salleh, Anna (December 8, 2011). "Cambrian predator had killer eyes". ABC Science. Retrieved 15 February 2012.
- Fossilised eyes of ancient super-predator found Australian Geographic December 9, 2011
References about Australian Trilobites:
- 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. Columbia University Press. ISBN 0231102542.
- Greg Edgecombe and the Australian Museum. "Australian Trilobites: A Species List and Bibliography". Retrieved August 23, 2005.
- Sam Gon III. "A guide to the Orders of Trilobites". Retrieved August 23, 2005.
- 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.
- Simpson, Dave. "Trilobites of South Australia". Retrieved August 23, 2005.