''Tuarangia'' is a Cambrian shelly fossil interpreted as an early

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

, though alternative classifications have been proposed and its systematic position remains controversial.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. Paläontologische Zeitschrift, 83(2), 267–291. doi:10.1007/s12542-009-0021-9 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''.

Description

''Tuarangia'' is a minute bivalve which was first described in 1982 by David I. MacKinnon of the

University of Canterbury The University of Canterbury (UC; ; postnominal abbreviation ''Cantuar.'' or ''Cant.'' for ''Cantuariensis'', the Latin name for Canterbury) is a public research university based in Christchurch, New Zealand. It was founded in 1873 as Canterbur ...

in Christchurch, New Zealand. Generally the shells of ''Tuarangia'' are subquadrate to trapezoidal and elongate in shape. The long hinge is straight with an indistinct umbone positioned close to the lateral midline of the hinge. The subparallel bar-like teeth of ''Tuarangia'' are taxodontic, and with a grouped into two rows with a ridge in between. An erect, narrow ligament is placed on the separating ridge. The shell structure of ''Tuarangia'' is noted for being composed of platy calcite sections in a zig-zag patterning. This is different from the shells of other Cambrian bivalves, which have a prismatic calcite shell and layers of carbonate

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 ...

which similar to the laminar aragonite layer found in extant monoplacophora. The genus name is taken from the Maori word ''tuarangi'', which means "ancient or of ancient date". ''Tuarangia paparua'' is based on the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen, UCM 923, and the paratype specimens, UCM 924-UCM 931, all of which are housed in the University of Canterbury Geology Department. The fossils were found in sediments of the late middle Cambrian aged Tasman Formation which outcrops west of

Cobb Reservoir The Cobb Reservoir is a hydro storage lake fed by the Cobb River in the Tasman District of the South Island of New Zealand. The reservoir feeds the Cobb Power Station and is above sea level but drops significantly with low rainfall. Cobb Reser ...

in the

Tasman Region Tasman District () is a local government district in the northwest of the South Island of New Zealand. It borders the Canterbury Region, West Coast Region, Marlborough Region and Nelson City. It is administered by the Tasman District Council, ...

, South Island, New Zealand. The specific epithet is from the Maori words ''papa'', which translates as "shell", and ''rua'', which means "two". The species would have lived along the coast of the

paleocontinent A paleocontinent or palaeocontinent is a distinct area of continental crust that existed as a major landmass in the geological past. There have been many different landmasses throughout Earth's time. They range in sizes; some are just a collection ...

Eastern Gondwana. The second species of ''Tuarangia'' to be described, ''Tuarangia gravgaerdensis'', is from sediments of the middle Cambrian aged Ardrarum Limestone Formation which outcrops on the island of

Bornholm Bornholm () is a List of islands of Denmark, Danish island in the Baltic Sea, to the east of the rest of Denmark, south of Sweden, northeast of Germany and north of Poland. Strategically located, Bornholm has been fought over for centuries. I ...

in the Baltic Sea.The Paleobiology database "At Olea" entry
accessed 9 January 2012 During the Cambrian Bornholm was a segment of ocean floor off the coast of the paleocontinet

Baltica Baltica is a paleocontinent that formed in the Paleoproterozoic and now constitutes northwestern Eurasia, or Europe north of the Trans-European Suture Zone and west of the Ural Mountains. The thick core of Baltica, the East European Craton, i ...

. The species was proposed by Berg-Madsen in 1987. The family Tuarangiidae and the order Tuarangiida were first proposed by MacKinnon in his 1982 paper on the genus. Since that description, the superfamily Tuarangiacea, which MacKinnon also proposed has been dropped from use. Tuarangiidae is now placed directly into the order Tuarangiida and the order is placed into the bivalve

evolutionary grade A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit. Phylogenetics The concept of evolutionary grades ...

Euprotobranchia. This puts Tuarangiida as a sister taxon to the order Fordillida. Euprotobranchia includes the earliest confirmed crown group bivalves to have been described, with ''Tuarangia'' being one of only four accepted bivalve genera to have been described from the Cambrian, the other three being '' Fordilla'', ''

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 Australi ...

'', and '' Camya''.

References

{{Taxonbar, from=Q7850652 Bivalve genera Prehistoric bivalves Prehistoric life of Europe Cambrian molluscs Fossil taxa described in 1982 Fossil taxa described in 1987