''Medusinites'' is a genus of disc shaped

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

ised organisms associated with the

Ediacaran biota The Ediacaran (; formerly Vendian) biota is a Taxonomy (biology), taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (). These were composed of enigmatic tubular and frond-sh ...

. They have been found in rocks dated to be 580 to 541 million years old.

Biology

Only three distinct species of ''Medusinites'' are known. They are similar to '' Protolyella'' in form and have an inner and outer ring. Specimens are typically 1–5 cm in

diameter In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...

and the

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

of its central disc is smaller than the width of the outer ring. They also have radial furrows and concentric circle features, but those details are not always preserved. They have been described as possibly living a lifestyle similar to a "stationary intermediate-level epifaunal osmotroph".

Distribution

''Medusinites''

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

have been found in

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

, and

Algeria ) , image_map = Algeria (centered orthographic projection).svg , map_caption = , image_map2 = , capital = Algiers , coordinates = , largest_city = capital , relig ...

. They are often found in

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

and

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tect ...

Classification

''Medusinites'' are in the

Phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

Cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that th ...

, which means they are related to other genera such as

Aspidella :Aspidella'' is also a homonym for the mushroom genus ''Saproamanita. ''Aspidella'' is an Ediacaran disk-shaped fossil of uncertain affinity. It is known from the single species ''A. terranovica''. Morphology ''Aspidella'' consists of disk-s ...

and

Cloudinidae The cloudinids, an early metazoan family containing the genera ''Acuticocloudina'', ''Cloudina'' and ''Conotubus'', lived in the late Ediacaran period about 550 million years ago. and became extinct at the base of the Cambrian. They formed mil ...

, and are essentially classified as

eumetazoa Eumetazoa (), also known as diploblasts, Epitheliozoa, or Histozoa, are a proposed basal animal clade as a sister group of the Porifera (sponges). The basal eumetazoan clades are the Ctenophora and the ParaHoxozoa. Placozoa is now also seen as a ...

ns, just like modern jellyfish. However, there have been several differing theories over the years about the placement of ''Medusinites'', as well as the

as a whole, and how many species there are within the genus. Several species within ''Medusinites'' have been moved to other genera or absorbed into other existing species, such as ''M. patellaris'', which was found to be a junior

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

for an

sp., and ''M. mawsoni'', which was assimilated into '' M. asteroides''. Regarding the debate over the nature of disc shaped

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...

fossils like ''Medusinites,'' there are two main opposing points of view''.'' A. Seilacher views the theory of them being soft bodied and jellyfish-like as problematic and suggests that they were more likely a unique type of

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

that had a "quilted" construction. Another view supported by Grazhdankin and Gerdes is that they were possibly a type of

microbial A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

colony.

Footnotes

{{Taxonbar, from=Q55138706 Ediacaran life Fossils of Australia Fossils of Canada Fossils of Norway