Click on the image to zoom
Sarawairhynchia zealandica (3 specimens to right of picture) from Highfield Farm
Amongst the Rhynconellida that turn up in the Triassic rocks of the Nelson area, some of the most distinctive and common are members of the genus Sakawairhynchia. A number of species are found, starting with S. zealandica in the Kaihikuan and then branching out into a number of other species (e.g. S. aparimaensis, S. nomeaensis, S. diptomaensis) in later stages. All are characterised by a roughly triangular to pentagonal outline and a convex dorsal valve, with 10-15 strong ribs which fade towards the umbo.
Most of the specimens in the collection come from a small area of Highfield Farm, and all occur in association with other typically Kaihikuan species, such as Alipunctifera kaihikuana. On this basis, they are believed to belong to the species S. zealandica. Although this can be a somewhat variable species, it is nevertheless distinctive because of its shape and characteristic ribbing. The image to the right shows specimens illustrated by MacFarlan (1992), Like many other brachiopods, various reclassifications have affected S. zealandica over the years, and it has previously been known as both Halorella zealandica and Rhynchonella zealandica. |
Sakawairhynchia zealandica
|
Specimens of Sakawairhynchia zealandica in the collection. Specimen LPC20_277 (top left) is from a donated collection; all other specimens have been collected from Highfield Farm.
Further Reading:
MacFarlan, D.A.B. 1992 Triassic and Jurassic Rhynchonellacea (Brachiopoda) from New Zealand & New Caledonia. Bulletin 31, The Royal Societ of New Zealand. Upper Hutt: The Royal Society of New Zealand.
MacFarlan, D.A.B. 1992 Triassic and Jurassic Rhynchonellacea (Brachiopoda) from New Zealand & New Caledonia. Bulletin 31, The Royal Societ of New Zealand. Upper Hutt: The Royal Society of New Zealand.
Description of species by D.A.B. MacFarlan (1992):
Moderate-sized rhynchonellide with rounded-triangular to triangular outline; moderately to well-inflated, with brachial valve more greatly inflated than pedicle valve. Pedicle valve with strongly rounded flanks, slightly convex to nearly flat central part posteriorly; broad, shallow, often indistinct sulcus anteriorly. Brachial valve moderately to strongly and evenly convex posteriorly; with indistinct fold anteriorly. Anterior commissure deflected by broad, distinct, flat-floored uniplication. Anterior margin usually straight; in some specimens, including lectotype, slightly concave in outline. In more inflated specimens anterior part of both valves curving towards commissure in both fold and sulcus, and on flanks. Some specimens geniculate near anterior margin.
Moderate-sized rhynchonellide with rounded-triangular to triangular outline; moderately to well-inflated, with brachial valve more greatly inflated than pedicle valve. Pedicle valve with strongly rounded flanks, slightly convex to nearly flat central part posteriorly; broad, shallow, often indistinct sulcus anteriorly. Brachial valve moderately to strongly and evenly convex posteriorly; with indistinct fold anteriorly. Anterior commissure deflected by broad, distinct, flat-floored uniplication. Anterior margin usually straight; in some specimens, including lectotype, slightly concave in outline. In more inflated specimens anterior part of both valves curving towards commissure in both fold and sulcus, and on flanks. Some specimens geniculate near anterior margin.