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Psioidea australis (LPC7_105) from Otamitan beds at Highfield Farm
According to the GNS's Fossil Record Electronic Database (FRED), Psioidea australis is a common species in the Triassic of the Nelson area, with finds from at least nineteen locations reported. The Psioidea beds are also considered distinctive features of the Late Triassic stratigraphy, and the species is a good marker for the Otamitan stage. It's therefore surprising that so far I have only recovered one certain specimen of the species.
Psioidea is a genus in the order Spriferida, and like others in this order is characterised by a long, straight hingeline, strong ribbing and a deep sulcus, matched by a fold in the opposing (dorsal) shell. A distinctive feature of P. australis is the way that the sides of the shell appear to straighten towards to top, and meet the higeline almost at right angles. Classification of the genus has nevertheless been controversial, and for some time Psioidea were regarded as a subgenus of the Spiriferina, while the lack of type specimens meant that individual species were not officially recognised. The description given by Trechmann (right) was thus under the name Spiriferina suessi var. australis. |
Psioidea australis
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Further Reading:
Marwick, J. 1953 Divisions and faunas of the Hokonui System (Triassic and Jurassic). Paleontological Bulletin 21, Wellington: New Zealand Geological Survey.
Trechmann, C.T. 1917 The Trias of New Zealand. Quarterly Journal of the Geological Society 291, 165-246 (+10 plates).
Marwick, J. 1953 Divisions and faunas of the Hokonui System (Triassic and Jurassic). Paleontological Bulletin 21, Wellington: New Zealand Geological Survey.
Trechmann, C.T. 1917 The Trias of New Zealand. Quarterly Journal of the Geological Society 291, 165-246 (+10 plates).