Pojetaia

Pojetaia; Temporal range: Upper Tommotian – lower Middle Cambrian PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Bivalvia
Order:	† Fordillida
Family:	† Fordillidae
Genus:	† Pojetaia ; Jell, 1980
Species
	See text.

Last updated November 19, 2024

Pojetaia is an extinct genus of early bivalves,^[1] one of two genera in the extinct family Fordillidae.^[2] The genus is known solely from Early to Middle Cambrian fossils found in North America, Greenland, Europe, North Africa, Asia, and Australia.^[2]^[3] 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.^[2]

Description

Pojetaia are small bivalves with valves that are subequal in size and suboval in shape. In size Pojetaia specimens reach a total shell length of less than 2 millimetres (0.079 in) and a height of 25 millimetres (0.98 in).^[2]^[4] The shells are compressed laterally and the back edge is slightly broadened. The rear adductor is more developed and larger than the front adductor, with the pallial muscles arranged in partially connected series along the valve margins.^[2] The ligament is usually straight with an umbo which is central to subcentral and each valve possessing between one and two teeth, with a total of no more than three teeth on a specimen. The exterior of the shells shows faint ribbing and fine comarginal growth lines.^[2] The inner shell layers of Fordilla and Pojetaia species both consist of layers of carbonate which is akin to the laminar aragonite layer found in extant monoplacophora.^[5] The structuring is similar to shell layering found in the extinct genera Anabarella and Watsonella , which is thought to suggest that members of the phylum Mollusca developed nacre independently several times.^[5] Due to the size and age of the fossil specimens, Pojetaia are included as part of the Turkish Small shelly fauna.^[2]

Affinity

Pojetaia and Fordilla appear to form a clade, but whether this is in the stem or crown group of Bivalvia is unconstrained by the available evidence.^[2]

Species

P. runnegari

The type species for Pojetaia, P. runnegari was first described by the Australian paleontologist Peter A. Jell in 1980.^[2] The description was based on fossils found in early Cambrian Parara Limestone sediments exposed in South Australia.^[2] The species has since been found in Cambrian strata of Greenland, Germany, Transbaikalia, Turkey, Northern China, and Mongolia. Fossils tentatively placed in Fordilla from the Browns Pond Formation of New York and Anse Maranda Formation of Quebec have been tentatively reassigned to Pojetaia runnegari.^[6] The species P. ostseensis was described in 1995 from two partial fossils found on the island of Bornholm. In his description of the species, Hinz-Schallreuter suggested the presence of three teeth on the left valve and the slightly larger size of the valves as reason for the erection of the new species. Other researchers, such as Elicki, have noted these differences fall into the accepted range of variation for P. runnegari and as such consider P. ostseensis as a synonym rather than valid. The genus Oryzoconcha, with the single species O. prisca, was described in 1985 by He and Pei from fossils found in Henan province, China. Further study by researches has resulted in genus and species being rejected, and the fossils assigned to P. runnegari. Similarly the genus Jellia and its two species J. elliptica and J. ovata, described by Li and Zhou in 1986, are also considered synonyms of P. runnegari as they fall into the rage of variation described for the species.^[2] 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.^[2]

P. sarhroensis

P. sarhroensis was named by Geyer and Streng in 1998 and is now known from a series of 49 fossils from early middle Cambrian sediments exposed in the Anti-Atlas mountains of Morocco. In the type description the major differences between P. sarhroensis and P. runnegari were noted to be fairly minor. The most distinct features of P. sarhroensis include occasional specimens with up to four teeth, a larger auricle angle, and a posterior tooth which is larger than that in P. runnegari.^[2]

Other fossils

It has been suggested at times that the problematic species Watsonella? terranovica may belong to Pojetaia as Pojetaia? terranovica. Reexamination of the species in 1991 by Landing resulted in the conclusion that the species may be a rostroconch from Watsonella or it may be a bivalve. Thus the positioning of the species is currently Watsonella? terranovica but with doubt.^[2]

Related Research Articles

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.

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.

The Pinnidae are a taxonomic family of large saltwater clams sometimes known as pen shells. They are marine bivalve molluscs in the order Pteriida.

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.

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.

Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks. Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The number of additional fossil species is estimated between 60,000 and 100,000, and the proportion of undescribed species is very high. Many taxa remain poorly studied.

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.

<i>Fordilla</i> Extinct genus of bivalves

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

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.

Tuarangia is a Cambrian shelly fossil interpreted as an early bivalve, though alternative classifications have been proposed and its systematic position remains controversial. It is the only genus in the extinct family Tuarangiidae and order Tuarangiida. The genus is known solely from Middle to Late Cambrian fossils found in Europe and New Zealand. The genus currently contains two accepted species, Tuarangia gravgaerdensis and the type species Tuarangia paparua.

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.

Hemiconcavodonta is an extinct genus of bivalve in the extinct family Praenuculidae. The genus is one of three genera in the subfamily Concavodontinae. Hemiconcavodonta is known solely from late Ordovician, Caradoc epoch, fossils found in South America. The genus currently contains a single accepted species, Hemiconcavodonta minuta.

Concavodontinae is an extinct subfamily of prehistoric bivalves in the family Praenuculidae. Concavodontinae species lived from the middle Ordovician, Caradoc epoch through the late Ordovician Ashgill epoch. Concavodontinae fossils are found in Europe 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 Concavodontinae was named by Teresa M. Sánchez in 1999.

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.

A hinge ligament is a crucial part of the anatomical structure of a bivalve shell, i.e. the shell of a bivalve mollusk. The shell of a bivalve has two valves and these are joined by the ligament at the dorsal edge of the shell. The ligament is made of a strong, flexible and elastic, fibrous, proteinaceous material which is usually pale brown, dark brown or black in color.

The adductor muscles are the main muscular system in bivalve mollusks. In many parts of the world, when people eat scallops, the adductor muscles are the only part of the animal which is eaten. Adductor muscles leave noticeable scars or marks on the interior of the shell's valves. Those marks are often used by scientists who are in the process of identifying empty shells to determine their correct taxonomic placement.

References

↑ Carter, J.G.; et al. (2011). "A Synoptical Classification of the Bivalvia (Mollusca)" (PDF). Paleontological Contributions. 4: 1–47.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 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.
↑ The Paleobiology Database Pojetaia entry accessed 4 January 2012
↑ Pojeta, J. (1975). "Fordilla troyensis Barrande and early pelecypod phylogeny". Bulletins of American Paleontology. 67: 363–384.
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 .
↑ 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.

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[Carter2011-1] Carter, J.G.; et al. (2011). "A Synoptical Classification of the Bivalvia (Mollusca)" (PDF). Paleontological Contributions. 4: 1–47.

[Elicki2009-2] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 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.

[PBDBPojetaia-3] The Paleobiology Database Pojetaia entry accessed 4 January 2012

[Pojeta1975-4] Pojeta, J. (1975). "Fordilla troyensis Barrande and early pelecypod phylogeny". Bulletins of American Paleontology. 67: 363–384.

[Vendrasco2011-5] 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 .

[Skovsted2007-6] 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.

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