The Emu Bay Shale is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

in Emu Bay, South Australia, containing a major Konservat-

Lagerstätte A Fossil-Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that preserves an exceptionally high amount of palaeontological information. ''Konzentrat-Lagerstätten'' preserv ...

(fossil beds with soft tissue preservation). It is one of two in the world containing

Redlichiida Redlichiida is an order of trilobites, a group of extinct marine arthropods. Species assigned to the order Redlichiida are among the first trilobites to appear in the fossil record, about halfway during the Lower Cambrian. Due to the difficul ...

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

s. The Emu Bay Shale is dated as Cambrian Series 2, Stage 4, correlated with the upper

Botomian Cambrian Stage 4 is the still unnamed fourth stage of the Cambrian and the upper stage of Cambrian Series 2. It follows Cambrian Stage 3 and lies below the Wuliuan. The lower boundary has not been formally defined by the International Commission ...

Stage of the

Lower Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovici ...

. Its mode of preservation is the same as the

Burgess shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...

, but the larger

grain size Grain size (or particle size) is the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which ...

of the Emu Bay rock means that the quality of preservation is lower. More than 50 species of

s, non-biomineralized

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

s (including megacheirans, nektaspids, and hymenocarines),

radiodonts Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and were used for a variety ...

palaeoscolecid The palaeoscolecids are a group of extinct ecdysozoan worms resembling armoured priapulids. They are known from the Lower Cambrian to the lower Ludfordian (late Silurian); they are mainly found as disarticulated sclerites, but are also preserved ...

s, a

lobopodia Lobopodians are members of the informal group Lobopodia (), or the formally erected phylum Lobopoda Cavalier-Smith (1998). They are panarthropods with stubby legs called lobopods, a term which may also be used as a common name of this group as ...

n, a

polychaete Polychaeta () is a paraphyletic class of generally marine Annelid, annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called c ...

vetulicolia Vetulicolia is a group of bilaterian marine animals encompassing several extinct species from the Cambrian, and possibly Ediacaran, periods. As of 2023, the majority of workers favor placing Vetulicolians in the stem group of the Chordata, but ...

ns, nectocaridids, hyoliths,

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

s, chancelloriids, several problematica and a

chelicerate The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, ticks ...

are known from the Emu Bay Shale.

Description

The Emu Bay Shale of

Kangaroo Island Kangaroo Island (, ) is Australia's third-largest island, after Tasmania and Melville Island, Northern Territory, Melville Island. It lies in the state of South Australia, southwest of Adelaide. Its closest point to the mainland is Snapper Poi ...

, South Australia, is Australia's only known Burgess-Shale-type Konservat-Lagerstätte, and includes faunal elements such as ''

Anomalocaris ''Anomalocaris'' (from Ancient Greek , meaning "unlike", and , meaning "shrimp", with the intended meaning "unlike other shrimp") is an extinct genus of radiodont, an order of early-diverging stem-group marine arthropods. It is best known fro ...

'', ''

Tuzoia ''Tuzoia'' (from Mount Tuzo, a mountain in the Canadian Rockies) is an extinct genus of large bivalved arthropod known from Early to Middle Cambrian marine environments from what is now North America, Australia, China, Europe and Siberia. The lar ...

'', ''

Isoxys ''Isoxys'' (meaning "equal surfaces") is a genus of extinct bivalved Cambrian arthropod; the various species of which are thought to have been freely swimming predators. It had a pair of large spherical eyes (which are the most commonly preserve ...

'', and '' Wronascolex'', in common with other Burgess-Shale-type assemblages, notably the Chengjiang Biota in China, the closest palaeogeographically, although somewhat older. A few genera of non-biomineralized arthropods, among them ''

Squamacula ''Squamacula'' is an extinct artiopodan arthropod from the Cambrian Series 2. The type species ''S. clypeata'' was described in 1997 from the Chengjiang biota of Yunnan, China. At the time of description there were only two known specimens of ''S ...

'', '' Kangacaris'', and the megacheiran '' Tanglangia'', are known only from the Emu Bay Shale and Chengjiang. The site is also the source of high-quality specimens of trilobites such as '' Redlichia takooensis'', '' Emuella polymera'', '' Balcoracania dailyi'', '' Megapharanaspis nedini'', '' Holyoakia simpsoni'', and '' Estaingia (=Hsuaspis) bilobata''. '' Balcoracania'' and '' Emuella'' are the only known genera of the distinctive

Redlichiina Redlichiina is a suborder of the order Redlichiida of Trilobites. The suborder contains three superfamilies: Emuelloidea, Redlichioidea and Paradoxidoidea. These trilobites are some of the oldest trilobites known. They originated at the beg ...

family

Emuellidae Emuellidae are a small family of trilobites, a group of extinct marine arthropods, that lived during the late Lower Cambrian (late Botomian) of the East Gondwana supercontinent, in what are today South-Australia and Antarctica. Description E ...

, known for possessing the greatest number of thoracic segments known for Trilobita as a whole (a record of 103 in one ''Balcoracania'' specimen), and so far entirely restricted to Australia and Antarctica. The

sedimentary depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will b ...

of the majority of Burgess-Shale-type assemblages is outer shelf, deeper water. The Emu Bay Shale in contrast, appears to represent deposition in restricted basins on the inner shelf, indicating that soft tissue preservation occurred in a range of environmental settings during the Cambrian. Various organisms inhabited the varying depths of the area, for example, the ''Estaingia'' and the "petalloids" from the site typically inhabited the deeper areas of the depositional environment, while in contrast, the ''Balcoracania'' found at the site typically lived within intertidal areas, such as tide pools. Some Emu Bay fossils display extensive mineralization of soft tissues, most often of blocky

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...

or fibrous

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

, including the oldest phosphatized muscle tissue – along with records from

Sirius Passet Sirius Passet is a Cambrian Lagerstätte in Peary Land, Greenland. The Sirius Passet Lagerstätte was named after the Slædepatruljen Sirius, Sirius sledge patrol that operates in North Greenland. It comprises six places in Nansen Land, on the eas ...

in Greenland, the first thus far reported from the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

. Mid-gut glands are preserved three-dimensionally in calcium phosphate in the arthropods ''Isoxys'' and ''Oestokerkus'', as in related species from the Burgess Shale. 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 ''Estaingia'', ''Redlichia'', hyolithids,

s, 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 ''Anomalocaris'', '' Echidnacaris'', ''Isoxys'', ''Tuzoia'', two species of the nektaspid arthropod family Emucarididae ('' Emucaris fava'' and '' Kangacaris zhangi''), the palaeoscolecid worm ''Wronascolex'', the problematic '' Myoscolex'', "petalloids" and '' Vetustovermis'', 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. Taxa documented from a quarry located inland of the shoreline exposure at Big Gully include '' Oestokerkus'', a genus of leanchoiliid closely related to the well-known ''

Leanchoilia ''Leanchoilia'' is a megacheiran marine arthropod known from Cambrian deposits of the Burgess Shale in Canada and the Chengjiang biota of China. Description ''L. superlata'' was about long and had long, whip-like flagellae extending from i ...

'', the early chelicerate '' Wisangocaris'' and the type species of a monotypic genus of artiopodan arthropod, ''

Australimicola ''Australimicola'' is a monotypic genus of ancient aquatic arthropods that are related to trilobites, they lived in the Cambrian period alongside them 538.8 million to 485.4 million years ago. Only a single species has been described in this genus ...

''. An armoured lobopodian of the Family Luolishaniidae is known from a single specimen that closely resembles the species ''Collinsovermis monstruosus'' from the Burgess Shale. In 2011, seven fossils of large, isolated

compound eye A compound eye is a Eye, visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidium, ommatidia, which are tiny independent photoreception units that consist of a cornea, lens (anatomy), lens, and p ...

s were described from the inland quarry site at Emu Bay, as well as the first well-preserved visual surfaces of the eyes of ''

''. The latter specimens are consistent with anomalocaridids being closely related to

s 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 more than 16,000 lenses, the resolution of the wide eyes would have been rivaled only by that of the modern

dragonfly A dragonfly is a flying insect belonging to the infraorder Anisoptera below the order Odonata. About 3,000 extant species of dragonflies are known. Most are tropical, with fewer species in temperate regions. Loss of wetland habitat threat ...

, which has 28,000 lenses in each eye.Fossilised eyes of ancient super-predator found

Australian Geographic Australian Geographic is a media business that produces the ''Australian Geographic'' and Australian Geographic Adventure magazine, australiangeographic.com.au and operates, either itself or business partners, Australian Geographic stores, Aus ...

December 9, 2011

Paleobiota

After Paterson et. al.(2015).

Arthropods

Other animals

References

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 th
Emu Bay page

External links

The Palaeontology of the Lower Cambrian Emu Bay Shale
{{DEFAULTSORT:Emu Bay Shale Cambrian System of Australia Shale formations Shallow marine deposits Fossiliferous stratigraphic units of Oceania Paleontology in Australia Geology of South Australia Kangaroo Island