Tuarangia is a minute bivalve which was first described in 1982 by David I. MacKinnon of the
University of Canterbury 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 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 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 in the
Tasman Region, 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 Eastern Gondwana. During the Cambrian Bornholm was a segment of ocean floor off the coast of the paleocontinet
Baltica. 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 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, and
Camya. ==References==