Click on the image to zoom
Dielasma zealandica, from Kaihikuan strata at Highfield Farm
Terebratulids make up only a small part of the brachipods found in the Triassic in New Zealand, with only two or three genera firmly identified. One of these is Dielasma. This comprises two named species: D zealandica, which seems to be restricted to the Kaihikauan and D. cf. himalayana which has been reported from the the Kaihikuan to Otamitan.
Distinction between the two species in not easy, but descriptions by Trechmann (1917) imply that D. zealandica is bigger and has a more prominent beak. On that basis, all the specimens of Dielasma found on Highfield Farm have been attributed to D. zealandica, and all have been found in a narrow area in rocks believed to be Kaihikuan in age. The typical shape of the species is shown in the images above and right. The right-hand image also shows (in the specimen on the left) how the pedicle on the ventral valve (in this case underneath) overhangs the dorsal valve. This can also be seen in several of the specimens shown in the gallery below. |
Dielasma zealandica
|
Specimens attributed to Dielasma zealandica
Further Reading:
Trechmann, C.T. 1917 The Trias of New Zealand. Quarterly Journal of the Geological Society 291, 165-246 (+ 10 plates).
Trechmann, C.T. 1917 The Trias of New Zealand. Quarterly Journal of the Geological Society 291, 165-246 (+ 10 plates).