| Emu Bay Shale | |
|---|---|
| Stratigraphic range: Cambrian Stage 4[1]("Lower Cambrian") | |
 North Coast of Kangaroo Island, Emu Bay | |
| Type | Geological formation |
| Unit of | Kangaroo Island Group |
| Underlies | Boxing Bay Formation |
| Overlies | Marsden Sandstone (unconformity) |
| Thickness | 78 m (256 ft), of which the lowest 10 m are fossiliferous |
| Lithology | |
| Primary | Shale |
| Other | Sandstone |
| Location | |
| Coordinates | 35°35′S137°30′E / 35.583°S 137.500°E /-35.583; 137.500 |
| Approximate paleocoordinates | 12°30′N161°12′W / 12.5°N 161.2°W /12.5; -161.2 |
| Region | The north coast ofKangaroo Island, aroundEmu Bay andCape D'Estaing,South Australia |
| Country | Australia |
| Type section | |
| Named for | Emu Bay |
TheEmu Bay Shale is ageological formation inEmu Bay, South Australia, containing a major Konservat-Lagerstätte (fossil beds with soft tissue preservation). It is one of two in the world containingRedlichiidantrilobites. The Emu Bay Shale is dated as Cambrian Series 2, Stage 4, correlated with the upperBotomian Stage of theLower Cambrian.[2]
Its mode of preservation isthe similar to theBurgess Shale, but the largergrain size of the Emu Bay rock means that the quality of preservation is lower.[3] More than 50 species oftrilobites, non-biomineralizedarthropods (includingmegacheirans,nektaspids, andhymenocarines),radiodonts,palaeoscolecids, alobopodian, apolychaete,vetulicolians,nectocaridids,hyoliths,brachiopods,sponges,chancelloriids, severalproblematica and achelicerate are known from the Emu Bay Shale.[4]
The Emu Bay Shale ofKangaroo Island, South Australia, is Australia's only known Burgess-Shale-type Konservat-Lagerstätte, and includes faunal elements such asAnomalocaris,Tuzoia,Isoxys, andWronascolex, in common with other Burgess-Shale-type assemblages, notably theChengjiang Biota in China, the closest palaeogeographically, although somewhat older. A few genera of non-biomineralized arthropods, among themSquamacula,Kangacaris, and the megacheiranTanglangia, are known only from the Emu Bay Shale and Chengjiang. The site is also the source of high-quality specimens of trilobites such asRedlichia takooensis,Emuella polymera,Balcoracania dailyi,Megapharanaspis nedini,Holyoakia simpsoni, andEstaingia (=Hsuaspis) bilobata.[5]Balcoracania andEmuella are the only known genera of the distinctiveRedlichiina familyEmuellidae, known for possessing the greatest number of thoracic segments known for Trilobita as a whole (a record of 103 in oneBalcoracania specimen), and so far entirely restricted to Australia and Antarctica.
Thesedimentary depositional environment 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, theEstaingia and the "petalloids" from the site typically inhabited the deeper areas of the depositional environment, while in contrast, theBalcoracania 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 blockyapatite or fibrouscalcium carbonate, including the oldest phosphatized muscle tissue – along with records fromSirius Passet in Greenland, the first thus far reported from theCambrian. Mid-gut glands are preserved three-dimensionally in calcium phosphate in the arthropodsIsoxys andOestokerkus, 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 ofEstaingia,Redlichia,hyolithids,brachiopods, and thescleritome-bearingChancelloria. 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, includingAnomalocaris,Echidnacaris,Isoxys,Tuzoia, two species of the nektaspid arthropod familyEmucarididae (Emucaris fava andKangacaris zhangi), the palaeoscolecid wormWronascolex, the problematicMyoscolex, "petalloids" andVetustovermis, and a number of rarer elements. The Big Gully trilobites rarely preserve any trace of non-biomineralized tissue; a small number of specimens ofRedlichia have been reported with antennae. Taxa documented from a quarry located inland of the shoreline exposure at Big Gully includeOestokerkus, a genus of leanchoiliid closely related to the well-knownLeanchoilia, the early chelicerateWisangocaris and the type species of a monotypic genus of artiopodan arthropod,Australimicola. An armoured lobopodian of the FamilyLuolishaniidae is known from a single specimen that closely resembles the speciesCollinsovermis monstruosus from the Burgess Shale.
In 2011, seven fossils of large, isolatedcompound eyes were described from the inland quarry site atEmu Bay, as well as the first well-preserved visual surfaces of the eyes ofAnomalocaris. The latter specimens are consistent with anomalocaridids being closely related toarthropods 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 withAnomalocaris and which were only able to sense night or day. With more than 24,000 lenses,[6] the resolution of the 3 centimetres (1.2 in) wide eyes would have been rivaled only by that of the moderndragonfly, which has 28,000 lenses in each eye.[7][8][9]
After Paterson et. al.(2015).[10]
| Arthropods | ||||
|---|---|---|---|---|
| Genus | Species | Notes | Images | |
| Anomalocaris | A. daleyae | A predatoryanomalocaridid radiodont closely related to the type species. |  | |
| Echidnacaris | E. briggsi | Afilter feedingtamisiocaridid radiodont, formerly known as"Anomalocaris" briggsi |  | |
| Wisangocaris | W. barbarahardyae | A stem-chelicerate belonging to theHabeliida, and adurophagous predator, with evidence of trilobite predation.[4] |  | |
| Tuzoia | T. australis, unnamed larger species | A large bivalvedhymemocarine, with a nearly cosmopolitan distribution. |  | |
| Isoxys | I. communis, I. glaessneri | An extremely common bivalved arthropod, and a key component of most Cambrian faunas. |  | |
| Oestokerkus | O. megacholix | Amegacheiran belonging to the family Leanchoiliidae |  | |
| Tanglangia[11] | T. rangatanga | Amegacheiran, a second species,T. longicaudata, is known from the earlier Chengjiang biota in China. |  | |
| Squamacula | S. buckorum | A basalartiopod, often classified as one of the most basal members of the group. |  | |
| Australimicola | A. spriggi | A basalartiopod |  | |
| Eozetetes | E. gemmelli | A vicissicaudatan artiopod, and is often considered to be a close relative ofAglaspidida. | ||
| Kangacaris | K. zhangi | Anektaspid artiopod belonging to the familyEmucarididae. A second species ofKangacaris,K. shui, is known from earlier deposits from China. |  | |
| Emucaris | Emucaris fava | |||
| Redlichia | R. takooensis,R. rex | Atrilobite belonging to the orderRedlichiida. One species from the area,R. rex, was carnivorous, and potentially cannibalistic.[12] |  | |
| Holyoakia | H. simpsoni | A trilobite belonging to the orderCorynexochida |  | |
| Megapharanaspis | M. nedini | A trilobite belonging to the order Redlichiida | ||
| Balcoracania | B. dailyi | A trilobite belonging to the order Redlichiida |  | |
| Emuella | E. polymera | A trilobite belonging to the order Redlichiida |  | |
| Estaingia | E. bilobata | A trilobite belonging to the order Redlichiida |  | |
| Non-arthropod animals | ||||
|---|---|---|---|---|
| Genus | Species | Notes | Images | |
| Nesonektris | N. aldridgei | A member ofVetulicolia, a group of basal chordates often considered to be close relatives of tunicates. |  | |
| Vetustovermis | A possible member ofNectocarididae, a controversial family of nektonic invertebrates. | |||
| Myoscolex | M. ateles | An enigmatic animal of unknown affinity, has been suggested to represent an annelid worm, or as a close relative ofOpabinia regalis.[13] |  | |
| "Petalloid"[10] | Indeterminate | An enigmatic, unnamed animal of unknown affinity that represents one of the most common benthic organisms from the biota. | ||
| Wronascolex | W. antiquus, W. iacoborum | Palaeoscolecid worm | ||
| Luolishaniidae[14] | Indeterminate | An armouredlobopodian, referred to as the "EBS Collin's Monster", and bears a similar appearance to the Burgess Shale speciesCollinsovermis monstruosus. | ||
| Chancelloria | C. australilonga | A member ofChancelloriidae, a group of spiny sponge-like animals. | ||
| Demospongiae[10] | Spp. | Sponges, predominantlyLeptomitidae, with minorHamptoniidae andChoiidae | ||
| "Eldonioid"[15] | Indeterminate | Related toEldonia | ||
| Brachiopoda[10] | Includes members of the familiesEoobolidae andBotsfordiidae | |||
| Hyolitha[10] | ||||
| Polychaeta[10] | Has possible affinities toBurgessochaeta. | |||
NOTE: Much of the text of this article was used with permission ofSam Gon III from his below referenced web site, in particular from theEmu Bay page
References about Australian trilobites: