''Ovatoscutum concentricum'' is one of many enigmatic organisms known from the

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 ...

deposits of the

Flinders Ranges The Flinders Ranges are the largest mountain range in South Australia, which starts about north of Adelaide. The ranges stretch for over from Port Pirie to Lake Callabonna. The Adnyamathanha people are the Aboriginal group who have inhabi ...

, Australia, and the White Sea area in Russia, dating around 555 Ma.

Etymology

The generic name ''Ovatoscutum'' is derived from the Latin ''ovatus'' (oval) and ''scutum'' (shield).

Description

This fossil has the form of a rounded shield, enclosing strongly concentric corrugations or ribs, which weaken adjacent to a triangular neckline. A suture-like zone extends through the center from the apex of the neckline towards the opposite margin. The ribs become wider towards the periphery. The symmetry of these ribs exhibits

glide reflection In 2-dimensional geometry, a glide reflection (or transflection) is a symmetry operation that consists of a reflection over a line and then translation along that line, combined into a single operation. The intermediate step between reflection ...

(opposite isometry); that is, the corresponding segments on the left and right sides do not line up, but are offset.

Affinity

''Ovatoscutum'' was first described by

Martin Glaessner Martin Fritz Glaessner AM (25 December 1906 – 23 November 1989) was a geologist and palaeontologist. Born and educated in the Austro-Hungarian Empire, he spent the majority of his life in working for geoscientific institutes in Austria, Russia ...

and

Mary Wade Mary Wade (17 December 1775 – 17 December 1859) was a British woman and convict who was transported to Australia when she was 13 years old. She was the youngest convict aboard , part of the Second Fleet. Her family grew to include five gener ...

in 1966, and this team tentatively interpreted it as a chondrophoran pneumatophore. This notion was based on morphologies apparently shared between ''Ovatoscutum'' and the

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

'' Plectodiscus'', leading to an interpretation of the organism as a velellid (pneumatophore), which itself bears a passing resemblance to the modern chondrophoran pneumatophore ''

Velella ''Velella'' is a monospecific genus of hydrozoa in the Porpitidae family. Its only known species is ''Velella velella'', a cosmopolitan free-floating hydrozoan that lives on the surface of the open ocean. It is commonly known by the names sea raf ...

''. Thus the hypothesis emerged that the ''Ovatoscutum'' was a

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

hydrozoa Hydrozoa (hydrozoans; ) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specializ ...

n chondrophoran. This hypothesis later became popular and was widely quoted, despite the absence of further research. As far back as 1966 Glaessner and Wade remarked that no evidence of a velellid 'sail' existed in ''Ovatoscutum'' and that ''Ovatoscutum'' differed from all other known porpitid chondrophorans. ''Ovatoscutum'' fossils are negative imprints on the bases of sandstone beds with the "elephant skin" and tubercle texture, diagnostic of

microbial mats A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria and archaea, or bacteria alone. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few survive in deserts. ...

. The same bedding planes contain various other

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

organisms: ''

Yorgia ''Yorgia waggoneri'' is a discoid Ediacaran organism. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of . It is classified within the extinct animal phylum Proarti ...

'', ''

Andiva ''Andiva ivantsovi'' is a Vendian fossil, identified to be a bilaterian triploblastic animal in the Ediacaran phylum Proarticulata, known from the Winter Coast, White Sea, Russia. It was first discovered in 1977, and described as a new species i ...

'', ''

Dickinsonia ''Dickinsonia'' is an extinct genus of basal animal that lived during the late Ediacaran period in what is now Australia, China, Russia and Ukraine. The individual ''Dickinsonia'' typically resembles a bilaterally symmetrical ribbed oval. Its a ...

'', ''

Tribrachidium ''Tribrachidium heraldicum'' is a tri-radially symmetric fossil animal that lived in the late Ediacaran (Vendian) seas. In life, it was hemispherical in form. ''T. heraldicum'' is the best known member of the extinct group Trilobozoa. Etymology ...

'', ''

Kimberella ''Kimberella'' is an extinct 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 gastropods, although its affinity with ...

'', ''

Parvancorina ''Parvancorina'' is a genus of shield-shaped bilaterally symmetrical fossil animal that lived in the late Ediacaran seafloor. It has some superficial similarities with the Cambrian trilobite-like arthropods. Etymology The generic name is derived ...

'' and others. The Ediacaran assemblages included in the bedding planes that were responsible for preserving the fossil forms of these benthic organisms are remarkably intact, indicating that they were mostly undisturbed during their burial and preservation ''

in situ ''In situ'' (; often not italicized in English) is a Latin phrase that translates literally to "on site" or "in position." It can mean "locally", "on site", "on the premises", or "in place" to describe where an event takes place and is used in ...

''. This mode of preservation thus argues against both a pelagic lifestyle and a chondrophoran interpretation of ''Ovatoscutum''.

Mikhail A. Fedonkin Academician Mikhail Aleksandrovich Fedonkin (russian: Михаи́л Алекса́ндрович Федо́нкин; born June 19, 1946) is a Russian paleontologist specializing in documentation of the earliest animals' body fossils, tracks, a ...

places ''Ovatoscutum'' in the extinct

bilateria The Bilateria or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly and ...

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 ...

Proarticulata Proarticulata is a proposed phylum of extinct, bilaterally symmetrical animals known from fossils found in the Ediacaran (Vendian) marine deposits, and dates to approximately . The name comes from the Greek () = "before" and Articulata, i.e. pr ...

. In the light of current morphological and taphonomic data, the precise nature of ''Ovatoscutum'' is still under consideration. Its affinities therefore remain unknown.

References

{{Taxonbar, from1=Q2322235, from2=Q20718918 Proarticulata Ediacaran life Fossils of Russia White Sea fossils Fossil taxa described in 1966

Etymology

Description

Affinity

See also

References