''Parvancorina'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of shield-shaped bilaterally symmetrical

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 ...

animal that lived in the late

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 t ...

seafloor. It has some superficial similarities with the

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

-like

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

Etymology

The generic name is derived from a

crasis Crasis (; from the Greek , "mixing", "blending"); cf. , "I mix" ''wine with water''; '' kratēr'' "mixing-bowl" is related. is a type of contraction in which two vowels or diphthongs merge into one new vowel or diphthong, making one word out of ...

compound word In linguistics, a compound is a lexeme (less precisely, a word or sign) that consists of more than one stem. Compounding, composition or nominal composition is the process of word formation that creates compound lexemes. Compounding occurs when ...

from the Latin ''parva ancora'' (small anchor). The specific name of the type species, ''P. minchami'', honors Mr. H. Mincham, the private collector, who in 1957 had collected and presented a number of fine specimens of Ediacaran fossils to the

South Australian Museum The South Australian Museum is a natural history museum and research institution in Adelaide, South Australia, founded in 1856 and owned by the Government of South Australia. It occupies a complex of buildings on North Terrace in the cultu ...

. The specific name of ''P. sagitta'' is the Latin word ''sagitta'' (arrow), in direct reference to the arrow-like shape.

Occurrence

''P. minchami'' fossils were first discovered in the Ediacara Member of the Rawnslay Quartzite,

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 inhabit ...

, in

South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest o ...

. This species is also known from deposits of the Verkhovka, Zimnegory and Yorga Formations in the

White Sea The White Sea (russian: Белое море, ''Béloye móre''; Karelian and fi, Vienanmeri, lit. Dvina Sea; yrk, Сэрако ямʼ, ''Serako yam'') is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is s ...

area of the

Arkhangelsk Region Arkhangelsk Oblast (russian: Арха́нгельская о́бласть, ''Arkhangelskaya oblast'') is a federal subject of Russia (an oblast). It includes the Arctic archipelagos of Franz Josef Land and Novaya Zemlya, as well as the Solovet ...

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...

. Additionally, similar poorly preserved ''Parvancorina'' sp. fossils were found in the Lyamtsa Formation of this Russian region. ''P. sagitta'' is found in the Verkhovka formation on the Solza River, White Sea area of the Arkhangelsk Region, Russia.

Description

It has a raised ridge down the central axis of symmetry. This ridge can be high in unflattened

s. At the 'head' end of the ridge there are two quarter-circle-shaped raised arcs attached. In front of this are two nested semicircular lines. Teeth seem to come from the raised parts pointing into the centre spaces. These may show as raised lines. The fossils are normally about in each of width and length, but can be up to .

Affinity

In attempting to determine its phylogenic relationships, ''Parvancorina'' has been compared with trilobite-like arthropods, such as '' Skania'' from the Burgess Shale Biota,

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 to ...

, and '' Primicaris'' from the

Chengjiang Biota The Maotianshan Shales are a series of Early Cambrian deposits in the Chiungchussu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized organisms or traces. The Maotianshan Shales ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...

. However, the growth form of ''Parvancorina'' is unusual for an arthropod, and its apparent sessile mode of life appears to rebut an arthropod affinity. Furthermore, the strong resemblance of ''P. sagitta'' to the primitive mollusk-like bilateran '' Temnoxa'' and similarities to parts of ''

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 t ...

'' casts further doubt on an arthropod affinity.

Lifestyle and habitus

The living ''Parvancorinas'' typically lived with their "heads" parallel to the current direction. Overfolding of the fossils from all sides contradicts any form of stalked attachment to the sea floor.

References

External links

Ediacaran.orgHome of the Ediacaran
* {{Taxonbar, from=Q763329 Ediacaran life Enigmatic prehistoric animal genera White Sea fossils Fossil taxa described in 1958