Eoandromeda
Encyclopedia
Eoandromeda is an Ediacaran
organism
consisting of eight radial spiral arms, and known from two taphonomic modes
: the standard Ediacara type preservation in Australia, and as carbonaceous compressions from the Doushantuo formation
of China,
where it is abundant.
specimens are known, ranging from about 1 to 4 cm in diameter; they are circular in outline and their eight arms, with closed ends, spiral either clockwise or anticlockwise.
Ridges cut across both the inside and outside of the spiral arms. The arms of the Australian individuals are longer and more tightly coiled than those of the Chinese, despite the Australian individuals not attaining as large a diameter; they are more often kinked.
, and has also been considered to represent an agglutinating foraminifera
n. However, the discovery of the Chinese fossils, which have preserved organic matter, ruled out these interpretations, because the Burgess shale type preservation
displayed required relatively robust organic material to start with. Its spiral form has also led to comparison with the fossil embryos
also preserved in the Doushantuo formation; the jury will remain out on this verdict until intermediate forms are found.
The organism bears a very superficial resemblance to echinoderm
s, ctenophore
s and some of the other Ediacara biota
, but lacks enough characters even to ascertain with certainty that it is indeed an animal
. If it is, it would be the earliest known fossil of an adult animal; and its anatomy is consistent with that expected from the earliest animals. However, it is not perfectly clear that it is an animal; algae
, the dominant constituent of the Doushantuo biota, cannot be ruled out, except that Eoandromeda seems a little too complex.
Trying to relate organisms that are preserved in the two modes is a nightmare, because they preserve such different parts of organisms; the imprints preserve a casts of the organism's outline, whereas the carbonaceous films display a shadow left by any resistant organic matter. This has made relating the two taphonomic types very difficult: Eoandromeda is one of the few organisms which can convincingly be compared in both taphonomic modes.
Such cases of preservation are known also for organisms related to the Anfesta-Albumares-like fossils from the Doushantuo Formation, for Beltanelloides sorichevae from the Lyamtsa Formation of the White Sea
area, Russia
and Doushantuo Formation, and possible for Cyclomedusa davidi
from Perevalok Formation of the Central Urals.
Ediacaran
The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
organism
Ediacara biota
The Ediacara biota consisted of enigmatic tubular and frond-shaped, mostly sessile organisms which lived during the Ediacaran Period . Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms.Simple multicellular organisms such as...
consisting of eight radial spiral arms, and known from two taphonomic modes
Taphonomy
Taphonomy is the study of decaying organisms over time and how they become fossilized . The term taphonomy was introduced to paleontology in 1940 by Russian scientist Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms, from the biosphere, to the...
: the standard Ediacara type preservation in Australia, and as carbonaceous compressions from the Doushantuo formation
Doushantuo Formation
The Doushantuo Formation is a Lagerstätte in Guizhou Province, China that is notable for being one of the oldest fossil beds to contain highly preserved fossils...
of China,
where it is abundant.
Morphology
A few dozen fossilFossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
specimens are known, ranging from about 1 to 4 cm in diameter; they are circular in outline and their eight arms, with closed ends, spiral either clockwise or anticlockwise.
Ridges cut across both the inside and outside of the spiral arms. The arms of the Australian individuals are longer and more tightly coiled than those of the Chinese, despite the Australian individuals not attaining as large a diameter; they are more often kinked.
Affinity
The organism was first interpreted as a trace fossilTrace fossil
Trace fossils, also called ichnofossils , are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings , urolites , footprints and feeding marks, and root cavities...
, and has also been considered to represent an agglutinating foraminifera
Foraminifera
The Foraminifera , or forams for short, are a large group of amoeboid protists which are among the commonest plankton species. They have reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net...
n. However, the discovery of the Chinese fossils, which have preserved organic matter, ruled out these interpretations, because the Burgess shale type preservation
Burgess shale type preservation
The Burgess Shale of British Columbia is famous for its exceptional preservation of mid-Cambrian organisms. Around 40 other sites have been discovered of a similar age, with soft tissues preserved in a similar, though not identical, fashion...
displayed required relatively robust organic material to start with. Its spiral form has also led to comparison with the fossil embryos
Fossil embryos
Fossil embryos are the preserved remains of organisms that have yet to hatch or be born. Many fossils of the Doushantuo formation have been interpreted as embryos; embryos are also common throughout the Cambrian fossil record.-Preservation:...
also preserved in the Doushantuo formation; the jury will remain out on this verdict until intermediate forms are found.
The organism bears a very superficial resemblance to echinoderm
Echinoderm
Echinoderms are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone....
s, ctenophore
Ctenophore
The Ctenophora are a phylum of animals that live in marine waters worldwide. Their most distinctive feature is the "combs", groups of cilia that they use for swimming, and they are the largest animals that swim by means of cilia – adults of various species range from a few millimeters to in size...
s and some of the other Ediacara biota
Ediacara biota
The Ediacara biota consisted of enigmatic tubular and frond-shaped, mostly sessile organisms which lived during the Ediacaran Period . Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms.Simple multicellular organisms such as...
, but lacks enough characters even to ascertain with certainty that it is indeed an animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
. If it is, it would be the earliest known fossil of an adult animal; and its anatomy is consistent with that expected from the earliest animals. However, it is not perfectly clear that it is an animal; algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
, the dominant constituent of the Doushantuo biota, cannot be ruled out, except that Eoandromeda seems a little too complex.
Taphonomic significance
In the Ediacaran (Vendian) period there are two biotas of multicellular organisms; as now understood, these biota do not generally share members, as was considered until recently:- Ediacara-type biota (it is in broad sense: Ediacara-, Nama-, Avalon-type ecological assemblage) it is community of the Metazoa and problematic organisms: DickinsoniaDickinsoniaDickinsonia is an iconic fossil of the Ediacaran biota. It resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; most interpretations consider it to be an animal, although others suggest it may be fungal, or a member of an "extinct kingdom".-Species variety:A...
, YorgiaYorgiaYorgia waggoneri is a member of the Ediacara biota, and resembles a cross between the organisms Dickinsonia and Spriggina. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of...
, KimberellaKimberellaKimberella is a monospecific genus of bilaterian known only from rocks of the Ediacaran period. The slug-like organism fed by scratching the microbial surface on which it dwelt in a manner similar to the molluscs, although its affinity with this group is contentious.Specimens were first found in...
, CharniaCharniaCharnia is the genus name given to a frond-like Ediacaran lifeform with segmented ridges branching alternately to the right and left from a zig-zag medial suture. The genus Charnia was named after Charnwood Forest in Leicestershire, England, where the first fossilised specimen was found.- Diversity...
, CharniodiscusCharniodiscusCharniodiscus is an Ediacaran fossil that was probably a stationary filter feeder that lived anchored to a sandy sea bed. The organism had a holdfast, stalk and frond. The holdfast was bulbous shaped, and the stalk was flexible. The frond was segmented and had a pointed tip...
, CyclomedusaCyclomedusaCyclomedusa is a circular fossil of the Ediacaran biota; it has a circular bump in the middle and as many as five circular growth ridges around it. Many specimens are small, but specimens in excess of 20cm are known. The concentric disks are not necessarily circular, especially when adjacent...
, EdiacariaEdiacariaEdiacaria is a fossil genus dating to the Ediacaran Period of the Neoproterozoic Era. Unlike most Ediacaran biota which disappeared almost entirely from the fossil record at the end of the Period, Ediacaria fossils have been found dating from the Baikalian age of the Upper Riphean to 501 million...
, ParvancorinaParvancorinaParvancorina is a genus of shield-shaped Ediacaran fossils. It has a raised ridge down the central axis of symmetry. This ridge can be high in unflattened fossils. At the 'head' end of the ridge there are two quarter circle shaped raised arcs attached. In front of this are two nested...
, PteridiniumPteridiniumPteridinium is an erniettomorph found in a number of Precambrian deposits worldwide. It is a member of the Ediacaran biota.-Body plan:It has a three-lobed body which is generally smashed flat such that only two lobes are visible. Each lobe consists of a number of parallel ribs extending back to the...
, RangeaRangeaRangea is a frond-like fossil of the Ediacaran period.The features found in Rangea are a double-layered quilted structure, a tripartite stemless body with fourfold radial symmetry, a mucous-supported sheath, smooth surface, radial membranes, and internal organs that are a system of sacs connected...
, FractofususFractofususFractofusus misrai is a fossil discovered in Newfoundland, Canada.- Discovery of vendian fossils in the Avalon Peninsula :In the summer of 1967, S.D.Misra an Indian graduate student at Newfoundland's Memorial University discovered a rich assemblage of imprints of soft bodied organisms on the...
, TribrachidiumTribrachidiumTribrachidium heraldicum was an early Ediacaran organism famous for its unusual tri-radial symmetry. It was named and first described from South Australia by Martin Glaessner and Brian Daily in 1959....
, HiemaloraHiemaloraHiemalora is a fossil of the Ediacaran biota, reaching around 3 cm in diameter, which superficially resembles a sea anemone. The genus has a sack-like body with faint radiating lines originally interpreted as tentacles, but discovery of a frond-like structure seemingly attached to some...
, palaeopascichnidsPalaeopascichnusPalaeopascichnus is a genus of Ediacaran organism comprising a series of lobes; it is plausibly a protozoan, but probably unrelated to the classical 'Ediacaran biota'....
and others. These organisms mainly are negative and positive imprints on the base of sandstone beds with the "elephant skin" and tubercle texture diagnostic of microbial matMicrobial matA microbial mat is a multi-layered sheet of micro-organisms, mainly bacteria and archaea. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces but a few survive in deserts. They colonize environments ranging in temperature from –40°C to +120°C...
s (Ediacara-type preservation), sandy casts in the beds of sandstone (Nama-type preservation), Avalon-type preservation characterized imprints on the top mudstone surface covered by volcanic ash, and in Khatyspyt-type preservation the fossils are found in finely laminated to medium-bedded, nodular bituminous limestones. - Miaohe-type biota characterizes assemblage of algal macrofossils: Beltanelloides, Mezenia, Sinospongia, Jiuqunaoella, Grypania, Liulingjitaenia, TawuiaTawuiaTawuia is a millimetric disc-shaped macrofossil from the Neoproterozoic. It is considered to be synonymous with Chuaria and Longfengshania....
, Calyptrina, Cucullus and others. These fossils are of the form of flat organic carbonaceous films; it is shadow left by organic matter of the organism flesh (it is looks like of the Burgess shale type preservationBurgess shale type preservationThe Burgess Shale of British Columbia is famous for its exceptional preservation of mid-Cambrian organisms. Around 40 other sites have been discovered of a similar age, with soft tissues preserved in a similar, though not identical, fashion...
).
Trying to relate organisms that are preserved in the two modes is a nightmare, because they preserve such different parts of organisms; the imprints preserve a casts of the organism's outline, whereas the carbonaceous films display a shadow left by any resistant organic matter. This has made relating the two taphonomic types very difficult: Eoandromeda is one of the few organisms which can convincingly be compared in both taphonomic modes.
Such cases of preservation are known also for organisms related to the Anfesta-Albumares-like fossils from the Doushantuo Formation, for Beltanelloides sorichevae from the Lyamtsa Formation of the White Sea
White Sea
The White Sea is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is surrounded by Karelia to the west, the Kola Peninsula to the north, and the Kanin Peninsula to the northeast. The whole of the White Sea is under Russian sovereignty and considered to be part of...
area, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
and Doushantuo Formation, and possible for Cyclomedusa davidi
Cyclomedusa
Cyclomedusa is a circular fossil of the Ediacaran biota; it has a circular bump in the middle and as many as five circular growth ridges around it. Many specimens are small, but specimens in excess of 20cm are known. The concentric disks are not necessarily circular, especially when adjacent...
from Perevalok Formation of the Central Urals.