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''Fordilla'' is an
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of early
bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
s, one of two genera in the extinct family
Fordillidae Fordillidae is an extinct family of early bivalves and one of two families in the extinct superfamily Fordilloidea. The family is known from fossils of early to middle Cambrian age found in North America, Greenland, Europe, the Middle East, A ...
. The genus is known solely from
Early 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 ( ...
fossils found in North America, Greenland, Europe, the Middle East, and Asia.The Paleobiology Database ''Fordilla'' entry
accessed 4 January 2012
The genus currently contains three described species, ''Fordilla germanica'', ''Fordilla sibirica'', and the type species ''Fordilla troyensis''.


Description

''Fordilla'' are small bivalves with
valves A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...
that are equal in size and suboval in shape. In size ''Fordilla'' specimens reach a total shell length of up to and a height of . The shells are compressed laterally and the back edge is slightly broadened. The rear adductor is less developed and smaller than the front adductor, while the small pedal retractor muscle scar is positioned near the front adductor scar. The valve hing is usually straight to slightly convexly curved and each valve will have at most one tooth present. The external surface of the shell occasionally show faint ribbing. The inner shell layers of ''Fordilla'' species, as with the related genus ''
Pojetaia ''Pojetaia'' is an extinct genus of early bivalves, one of two genera in the extinct family Fordillidae. The genus is known solely from Early to Middle Cambrian fossils found in North America, Greenland, Europe, North Africa, Asia, and Austral ...
'', consist of layers of carbonate which is akin to the laminar aragonite layer found in extant monoplacophora. The structuring is similar to shell layering found in the extinct genera ''
Anabarella ''Anabarella'' is a species of bilaterally-flattened monoplacophoran mollusc, with a morphological similarity to the rostroconchs. Its shell preserves evidence of three mineralogical textures on its outer surface: it is polygonal near the crest ...
'' and ''
Watsonella ''Watsonella'' is a genus of 'mollusc' known from early (Terreneuvian) Cambrian strata. The genus is closely related to '' Anabarella'', with which it bears many morphological similarities, including a laminar internal shell microstructure said ...
'' which is thought to suggest members of the phylum
Mollusca Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is esti ...
developed
nacre Nacre ( , ), also known as mother of pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is f ...
independently several times. Due to the size and age of the fossil specimens, ''Fordilla'' are included as part of the Turkish
Small shelly fauna The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambri ...
.


Species


''F. germanica''

Described in 1994, ''F. germanica'' is the most recent valid species of ''Fordilla'' to be described. As the species
etymology Etymology ()The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the Phonological chan ...
indicates, the species was first described from strata of the Zwetau Formation in Germany, with the type locality at
Görlitz Görlitz (; pl, Zgorzelec, hsb, Zhorjelc, cz, Zhořelec, :de:Ostlausitzer Mundart, East Lusatian dialect: ''Gerlz'', ''Gerltz'', ''Gerltsch'') is a town in the Germany, German state of Saxony. It is located on the Lusatian Neisse River, and ...
,
Saxony Saxony (german: Sachsen ; Upper Saxon: ''Saggsn''; hsb, Sakska), officially the Free State of Saxony (german: Freistaat Sachsen, links=no ; Upper Saxon: ''Freischdaad Saggsn''; hsb, Swobodny stat Sakska, links=no), is a landlocked state of ...
. The species is identifiable from the other two ''Fordilla'' species by the more elongated shape of the valves, the straight dorsal edge which has a slight tilt, and by the muscle arrangement. The shells reach up to long, by wide and tall. The placement of ''F. germanica'' questioned by Geyer and Streng in 1998 who, noting the size of the specimens, moved the species to ''Pojetaia'' as ''P. germanica''. This move was rejected by subsequent authors and the species moved back to ''Fordilla'' by Elicki in 2009.


''F. sibirica''

''F. sibirica'' was named by I.N. Krasilova in 1977 based on a series of about 20 fossils from the Tyuser Formation in Northeastern Siberia. Since the species description opinions have differed on the validity of its status, with several studies synonymizing it with ''F. troyensis''. The original description cited the placement and more rounded outline of the front adductor scar along with the morphology of dorsal edge as reason for erection of the new species.


''F. troyensis''

The
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...
for ''Fordilla'', ''F. troyensis'' was first described by the French
paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
Joachim Barrande Joachim Barrande (11 August 1799 – 5 October 1883) was a French geologist and palaeontologist. Career Barrande was born at Saugues, Haute Loire, and educated in the École Polytechnique and École Nationale des Ponts et Chaussées at Paris. Al ...
in 1881. The description was based on a group of five fossils found in Cambrian sediments exposed at
Troy, New York Troy is a city in the U.S. state of New York and the county seat of Rensselaer County. The city is located on the western edge of Rensselaer County and on the eastern bank of the Hudson River. Troy has close ties to the nearby cities of Albany a ...
and purchased by S.W. Ford. The species has since been found in Cambrian strata of Greenland and Newfoundland in North America. Specimens have been confirmed from the
island of Bornholm An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerry, skerries, cays or keys. An r ...
,
Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Danish Realm, Kingdom of Denmark ...
. Fossils tentatively placed in ''Fordilla'' from the Browns Pond Formation of New York and Anse Maranda Formation of Quebec have been reassigned to ''Pojetaia runnegari''.


Other fossils

Additional fossils have been attributed to the genus since its description. A fossil from
North Attleboro, Massachusetts North Attleborough, alternatively spelled North Attleboro, is a town in Bristol County, Massachusetts, United States. The population was 30,834 at the 2020 United States Census. The villages of Attleboro Falls and North Attleborough Center are ...
was placed in the genus by Shaler and Foerste in 1888, however this specimen was later determined to be a possible fossil of ''Heraultia''. Fossils form
Hartshill Hartshill is a large village and civil parish in North Warwickshire, England, 2.5 miles (4 km) north-west of the town of Nuneaton. The parish borders the district of Nuneaton and Bedworth at the south, the North Warwickshire district parishes ...
,
North Warwickshire North Warwickshire is a local government district with borough status in the ceremonial county of Warwickshire, West Midlands, England. Outlying settlements in the borough include the two towns of Atherstone (where the council is based) and Co ...
, England and the lower Cambrian of Portugal have been tentatively placed into ''Fordilla'' without assignment to species. Specimens from
Zaragoza Zaragoza, also known in English as Saragossa,''Encyclopædia Britannica'"Zaragoza (conventional Saragossa)" is the capital city of the Zaragoza Province and of the autonomous community of Aragon, Spain. It lies by the Ebro river and its tributari ...
, Spain were placed into ''Fordilla'' with the name ''Fordilla marini'' but the size and shape of the specimens indicates they do not belong to the genus. The cryptic genus ''Buluniella'' and species ''B. borealis'' was described in 1986 by V. Jermak from three fossils found in Northern Siberia. The two right and one left disarticulated valves known show a slightly convexity of the hinge, central umbo and lack of a row of muscle scars were used to the genus from ''Fordilla''. The less distinct umbones were suggested as reason to separate ''Buluniella'' from ''Pojetaia''. Due to the high variation in characters of Cambrian bivalve species the validity of ''Buluniella'' as a separate genus and species has been questioned several times. In 1992
Bruce Runnegar Bruce Norman Runnegar (born 2 February 1941, Brisbane) is an Australian-born paleontologist and professor at UCLA. His research centers on using the fossil record to determine how, where, and when life originated and evolved. He has published on ...
and Pojeta recommended ''Buluniella'' belonged to ''Fordilla'' and suggested the species be treated as ''Fordilla borealis''. Further examination of the fossils has resulted in both the genus and the species being currently treated as a synonym of ''P. runnegari''.


References

{{Taxonbar, from=Q5468091 Prehistoric bivalve genera Prehistoric life of Europe Cambrian molluscs Fossil taxa described in 1881 Paleozoic life of Newfoundland and Labrador Paleozoic life of Nova Scotia Taxa named by Joachim Barrande