Click on the image to zoom
Dorsal valve, with shell
|
Alipunctifera kaihikuana
Order: Brachiopod
Genus: Alipunctifera Species: Alipunctifera kaihikuana Location found: 88 Valley, Wakefield |
Alipunctifera kaihikuana (previously Spiriferina kaihikuana) is a key species from the Triassic of New Zealand, for it is an unambiguous marker for the Kaihikuan stage. This is the first stage in the Triassic to show a wealth of fossil evidence and to signal recovery from the Great Dying at the end of the Permian.
The species is relatively easy to identify, showing many of the features of the Spiriferida order, to which it belongs. The specimen above is the dorsal valve and at close inspection (zoom in on the lower left side) shows the punctae which are a diagnostic feature, and contribute to its generic name. The prominent median fold on this valve can also be seen, together with the further five folds (ribs) on either side, diminishing in strength. On the ventral valve, the median fold is matched by a deep sulcus (see image right). Other distinguishing features are the very strong, divided beak on the ventral valve and the elongated and straight hingeline. Note also the difference in shape between the two valves. The ventral is wider and more flared than the dorsal valve. It may also be noted, in this specimen, that the punctae are visible even though the shell is lacking and all that remains is an internal cast. This indicates the way in which the punctae puncture the shell, perhaps providing an aid for respiration and/or waste release. Further specimens are shown in the images below. |
Ventral valve. (Note, specimen lacks shell, so shows only the internal cast)
Detailed description (from Trechmann 1917) The area is broad, and extends the whole length of the wings. Some specimens are more sharply alate than others ; but in all of them the hinge-line represents the greatest width of the shell, and the margin contracts rapidly in front of the wings. The ventral valve has a broad, concave, median, rapidly-widening, dorsal furrow with about six low rounded folds on each side of it. The dorsal valve has a broad, rounded, median fold with five to seven low rounded folds on each side, which gradually diminish in size. The folds occupy the surface of the shell nearly to the hinge-area. The growth-lines are rather coarse. To see a gallery of specimens from Highfield Farm,
click the button below: |
Ventral valve, part shelled (left); internal cast of ventral valve (centre); full internal cast seen from dorsal side (right)
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).