Fordilla

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Fordilla
Temporal range: Cambrian 520.0–516.0  Ma
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Fordilla troyensis.png
F. troyensis; outer shell surface (top) and cast of internal anatomy [1]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order:† Fordillida
Family:† Fordillidae
Genus:† Fordilla
Barrande, 1881
Species

See text

Fordilla is an extinct genus of early bivalves, [2] [3] [4] [5] [6] one of two genera in the extinct family Fordillidae. [7] The genus is known solely from Early Cambrian fossils found in North America, Greenland, Europe, the Middle East, and Asia. [8] The genus currently contains three described species, Fordilla germanica, Fordilla sibirica, and the type species Fordilla troyensis. [7] [8]

Contents

Description

Fordilla are small bivalves with valves that are equal in size and suboval in shape. In size Fordilla specimens reach a total shell length of up to 4 millimetres (0.16 in) and a height of 2.5 millimetres (0.098 in). [7] [9] 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. [7] The valve hinge 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. [7] The inner shell layers of Fordilla species, as with the related genus Pojetaia , consist of layers of carbonate which is akin to the laminar aragonite layer found in extant monoplacophora. [10] The structuring is similar to shell layering found in the extinct genera Anabarella and Watsonella which is thought to suggest members of the phylum Mollusca developed nacre independently several times. [10] Due to the size and age of the fossil specimens, Fordilla are included as part of the Turkish Small shelly fauna. [7]

Species

F. germanica

Described in 1994, F. germanica is the most recent valid species of Fordilla to be described. As the species etymology indicates, the species was first described from strata of the Zwetau Formation in Germany, with the type locality at Görlitz, Saxony. 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 3.8 millimetres (0.15 in) long, by 1.8 millimetres (0.071 in) wide and 1.1 millimetres (0.043 in) tall. [11] 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. [7]

F. sibirica

F. sibirica was named by I.N. Krasilova in 1977 based on a series of about 20 fossils [7] from the Tyuser Formation in Northeastern Siberia. [8] 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. [7]

F. troyensis

The type species for Fordilla, F. troyensis was first described by the French paleontologist Joachim Barrande in 1881. [8] The description was based on a group of five fossils found in Cambrian sediments exposed at Troy, New York and purchased by S.W. Ford. [12] 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, 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. [13]

Other fossils

Additional fossils have been attributed to the genus since its description. [9] A fossil from North Attleboro, Massachusetts 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, North Warwickshire, England and the lower Cambrian of Portugal have been tentatively placed into Fordilla without assignment to species. Specimens from Zaragoza, 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. [9] 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 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. [7]

Related Research Articles

<span class="mw-page-title-main">Bivalvia</span> Class of molluscs

Bivalvia or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs that have laterally compressed soft bodies enclosed by a calcified exoskeleton consisting of a hinged pair of half-shells known as valves. As a group, bivalves have no head and lack some typical molluscan organs such as the radula and the odontophore. Their gills have evolved into ctenidia, specialised organs for feeding and breathing.

<span class="mw-page-title-main">Rostroconchia</span> Extinct class of molluscs

The Rostroconchia is a class of extinct molluscs dating from the early Cambrian to the Late Permian. They were initially thought to be bivalves, but were later given their own class. They have a single shell in their larval stage, and the adult typically has a single, pseudo-bivalved shell enclosing the mantle and muscular foot. The anterior part of the shell probably pointed downward and had a gap from which the foot could probably emerge. Rostroconchs probably lived a sedentary semi-infaunal lifestyle. There were probably more than 1,000 species of members of this class.

<span class="mw-page-title-main">Evolution of molluscs</span> The origin and diversification of molluscs through geologic time

The evolution of the molluscs is the way in which the Mollusca, one of the largest groups of invertebrate animals, evolved. This phylum includes gastropods, bivalves, scaphopods, cephalopods, and several other groups. The fossil record of mollusks is relatively complete, and they are well represented in most fossil-bearing marine strata. Very early organisms which have dubiously been compared to molluscs include Kimberella and Odontogriphus.

<i>Yochelcionella</i> Extinct genus of molluscs

Yochelcionella is an extinct genus of basal molluscs which lived during the Tommotian epoch, the first epoch of the Cambrian period. This genus is often reconstructed to resemble snails.

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1985.

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1881.

<span class="mw-page-title-main">Helcionellid</span> Extinct order of molluscs

Helcionellid or Helcionelliformes is an order of small fossil shells that are universally interpreted as molluscs, though no sources spell out why this taxonomic interpretation is preferred. These animals are first found about 540 to 530 million years ago in the late Nemakit-Daldynian age, which is the earliest part of the Cambrian period. A single species persisted to the Early Ordovician. These fossils are component of the small shelly fossils (SSF) assemblages.

<span class="mw-page-title-main">Mollusc shell</span> Exoskeleton of an animal in the phylum Mollusca

The molluscshell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes. Not all shelled molluscs live in the sea; many live on the land and in freshwater.

<span class="mw-page-title-main">Mollusca</span> Phylum of invertebrate animals

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Stenothecidae is an extinct family of fossil univalved Cambrian molluscs which may be either gastropods or monoplacophorans.

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 of the shell, subsequently changing to both spiny and stepwise. Its internal microstructure is calcitic and semi-nacreous. Its name reflects its provenance from Anabar, Siberia. It has been interpreted as ancestral to the rostroconchs, and has been aligned to the Helcionellidae.

Stenothecoida is a taxon of bivalved fossils from the Early to middle Cambrian period. They look a bit like brachiopods or bivalve molluscs.

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 Australia. The genus currently contains two accepted species, Pojetaia runnegari, the type species, and Pojetaia sarhroensis, though up to seven species have been proposed. The genera Buluniella, Jellia, and Oryzoconcha are all considered synonyms of Pojetaia.

Watsonella is an extinct genus of mollusc known from early (Terreneuvian) Cambrian strata. It has been hypothesized to be close to the origin of bivalves. It contains a single species, Watsonella crosbyi.

<span class="mw-page-title-main">Fordillidae</span> Extinct family of bivalves

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, Asia, and Australia. The family currently contains two genera, Fordilla and Pojetaia, each with up to three described species. Due to the size and age of the fossil specimens, Fordillidae species are included as part of the Turkish Small shelly fauna.

Camya is an extinct genus of early bivalve and is the only genus in the extinct family Camyidae. The genus is known solely from early Middle Cambrian fossils found in Europe. The genus currently contains a solitary accepted species, Camya asy.

<span class="mw-page-title-main">Fordilloidea</span> Extinct superfamily of bivalves

Fordilloidea is an extinct superfamily of early bivalves containing two described families, Fordillidae and Camyidae and the only superfamily in the order Fordillida. The superfamily is known from fossils of early to middle Cambrian age found in North America, Greenland, Europe, the Middle East, Asia, and Australia. Fordillidae currently contains two genera, Fordilla and Pojetaia each with up to three described species while Camyidae only contains a single genus Camya with one described species, Camya asy. Due to the size and age of the fossil specimens, Fordillidae species are included as part of the Turkish Small shelly fauna.

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Concavodonta is an extinct genus of early bivalve in the extinct family Praenuculidae. The genus is one of three genera in the subfamily Concavodontinae. Concavodonta is known solely from late Ordovician, Caradoc epoch, fossils found in Europe and South America. The genus currently contains three accepted species, Concavodonta imbricata, Concavodonta ovalis and the type species Concavodonta ponderata.

Praenuculinae is an extinct subfamily of prehistoric bivalves in the family Praenuculidae. Praenuculinae species lived from the middle Ordovician through the late Devonian. Praenuculinae fossils are found in Europe, Africa, North America and South America, and species are thought to have been stationary attached to substrate in shallow infaunal marine water environments where they formed shells of an aragonite composition. The subfamily Praenuculinae was named by Teresa M. Sánchez in 1999.

References

  1. ↑ Charles Doolittle Walcott (1886). Second contribution to the studies on the Cambrian faunas of North America. Vol. 30 of Geological Survey bulletin. Govt. Print. Off. pp. 1–369.
  2. ↑ Carter, J.G.; et al. (2011). "A Synoptical Classification of the Bivalvia (Mollusca)" (PDF). Paleontological Contributions. 4: 1–47.
  3. ↑ Pojeta, J. (2000). "Cambrian Pelecypoda (Mollusca)". American Malacological Bulletin . 15: 157–166.
  4. ↑ Schneider, J. A. (November 2001). "Bivalve systematics during the 20th century". Journal of Paleontology . 75 (6): 1119–1127. doi:10.1666/0022-3360(2001)075<1119:BSDTC>2.0.CO;2 . Retrieved 2008-10-05.
  5. ↑ Gubanov, A.P.; Kouchinsky, A.V.; Peel, J.S. (2007). "The first evolutionary-adaptive lineage within fossil molluscs". Lethaia . 32 (2): 155–157. doi:10.1111/j.1502-3931.1999.tb00534.x.
  6. ↑ Gubanov, A.P.; Peel, J.S. (2003). "The early Cambrian helcionelloid mollusc Anabarella Vostokova". Palaeontology . 46 (5): 1073–1087. doi: 10.1111/1475-4983.00334 . S2CID   84893338.
  7. 1 2 3 4 5 6 7 8 9 10 Elicki, O.; Gürsu, S. (2009). "First record of Pojetaia runnegari Jell, 1980 and Fordilla Barrande, 1881 from the Middle East (Taurus Mountains, Turkey) and critical review of Cambrian bivalves" (PDF). Paläontologische Zeitschrift. 83 (2): 267–291. doi:10.1007/s12542-009-0021-9. S2CID   49380913. Archived from the original (PDF) on 2013-10-29. Retrieved 2012-01-06.
  8. 1 2 3 4 The Paleobiology Database Fordilla entry accessed 4 January 2012
  9. 1 2 3 Pojeta, J. (1975). "Fordilla troyensis Barrande and early pelecypod phylogeny". Bulletins of American Paleontology. 67: 363–384. Archived from the original on 2012-01-06.
  10. 1 2 Vendrasco, M.J.; Checa, A.G.; Kouchinsky, A.V. (2011). "Shell microstructure of the early bivalve Pojetaia and the independent origin of nacre within the Mollusca". Palaeontology. 54 (4): 825–850. doi: 10.1111/j.1475-4983.2011.01056.x .
  11. ↑ Elicki, O. (1994). "Lower Cambrian carbonates from eastern Germany: Palaeontology, stratigraphy and palaeogeography" (PDF). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 191 (1): 69–93.
  12. ↑ Clarke, J.M.; Ruedemann, R. (1903). "Catalogue of type specimens of Paleozoic fossils in New York State Museum". New York State Museum Bulletin. 65 (Paleontology 8): 385. doi: 10.5962/bhl.title.32922 .
  13. ↑ Skovsted, C.B.; Peel, J.S. (2007). "Small shelly fossils from the argillaceous facies of the Lower Cambrian Forteau Formation of western Newfoundland" (PDF). Acta Palaeontologica Polonica. 52 (4): 729–748.[ permanent dead link ]
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