Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 4c): GS11650, J40/f6612, Waihao River, near "Pentland Hills", Mangaorapan ? (GNS)
(Pl. 4g): GS11650, J40/f6612, Waihao River, near "Pentland Hills", Mangaorapan ? (GNS)
Beu & Maxwell (1990): Chapter 6; p. 90; pl. 4 c, g.
Description: Rather small for genus (height 35 mm), known only by the little-inflated, unattached left valve. Ears subequal, small. Radial sculpture of about 30 narrow, finely spinose costae, some with smooth or weakly spinose or scaly costellae in between, in places as strong as primary costae. Commarginal sculpture of very fine growth lines. Cardinal area very narrow; resilifer narrowly triangular, separated from prominent sockets on either side by narrow ridges. Crura large, upturned, adjacent to sockets. Adductor muscle scar large, sub-circular. Internal margin finely crenulate.
Comparison: The new species is very similar to Spondylus aucklandicus (Otaian-Clifdenian, Northland, Westland and Southland) but has relatively stronger secondary radial costae. Spondylus is generally regarded as an indicator of warm-water (subtropical or tropical) conditions, although S. tenellus Reeve, 1856 lives today in Tasmania and other parts of southern Australia, and S. sparsispinosus Dall, Bartsch and Rehder, 1938 lives in deep water off northern New Zealand, as far south as off White Island, Bay of Plenty (Dijkstra & Marshall 2008, p. 79). The genus is recorded from the Late Cretaceous in New Zealand, but for a long time it was thought that the only Cenozoic occurrences were of Early Miocene age. More recent collecting has steadily increased its stratigraphic range, and it is now known to have been present from at least earliest Eocene (Waipawan, Chatham Islands) to Late Miocene (Waiauan, Waikuku Beach, North Cape). The record is very sporadic but the fact that the species illustrated here and shells from Matanginui Limestone (Waipawan) on Chatham Island are very similar to the Early Miocene S. aucklandicus suggests that Spondylus has been present continuously in the New Zealand region from at least Early Eocene to Middle Miocene. The alternative possibility, that the scattered occurrences of Spondylus all represent independent, short-lived dispersals, seems less likely.
Distribution: Mangaorapan(?), Kauru Formation, South Branch, Waihao River near "Pentland Hills" in shell-rich greensand with abundant corals (not common).
Cite this publication as: "A.G. Beu and J.I. Raine (2009). Revised
descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990). GNS
Science miscellaneous series no. 27."
© GNS Science, 2009
(Included with a PDF facsimile file copy of New Zealand Geological Survey Paleontological Bulletin 58 in CD version from: Publications Officer, GNS Science, P.O. Box 30368 Lower Hutt, New Zealand)