GNS Science

Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)

New Zealand Cenozoic Mollusca

Kotakaia simplex Beu, 1988


(Pl. 4p): Holotype, GS12173, CH/f478, neck of Tarawhenua Peninsula, Pitt Island, Waipawan (TM6785, GNS)

Beu & Maxwell (1990): Chapter 6; p. 97; pl. 4 p.

Synonymy: Kotakaia simplex Beu 1988, p. 92

Type species of Kotakaia Beu, 1988

Classification: Personidae

Description: Small for family (16-18 mm high; probably originally 22 mm high), with evenly rounded whorls, simple spiral sculpture, low wide varices every 0.67 whorl down teleoconch, and a heavily but simply armed aperture. Protoconch not seen. Sculpture of low, widely spaced spiral cords, 5 on spire whorls and about 12 on last whorl and neck, with several more very weak ones on siphonal canal; the better-preserved specimens have all spiral interspaces filled by a low, wide secondary cord; no axial sculpture visible, other than varices. Aperture elongate-oval, strongly constricted by heavy armature. Outer lip thick, protruding well beyond terminal varix, tapering rapidly to a thin edge, bearing 4 large, narrowly rounded ridges inside. Inner lip smooth except for a single high, narrow parietal ridge, forming (with uppermost ridge inside outer lip) a strongly constricted posterior sinus at top of aperture; and a row of 3 (or, in one specimen, 4) ridges on base of columella. Basal columellar ridges situated on a raised callus ridge protruding strongly into aperture, decreasing markedly in prominence as they descend left edge of short, straight, widely open, left- directed siphonal canal. All apertural ridges long, truly spiral features extending well inside aperture. Outer (left) edge of inner lip thick and well raised above previous whorl.

Comparison: This simply shaped, undistorted, simply sculptured, but heavily armed little shell is one of the most curious Personidae to come to light so far. It could have been a contender for the ancestor of the Personidae, had Cottreau (1922, p. 66, pl. 9, fig. 4-7) not described, in Eutritonium praegranosum, a Madagascan Campanian (Late Cretaceous) species of Distorsio (sensu stricto), to judge from the relatively large size (34 x 20.5 mm), strong coiling distortion, and coarsely cancellate sculpture evident on Cottreau's internal moulds. An interesting connotation of this Campanian Distorsio species is that Distorsio and Sassia (see above) are both now recognised in Late Cretaceous rocks, so Personidae apparently evolved independently of the Ranellidae, and Beu (1988) recognised Personidae as a separate family of Tonnoidea.

The genus Personopsis Beu, 1988 (= Personella, not of Conrad) differs from Distorsio in its smaller size, and in having the basal columellar ridges situated directly on the columella, not protruding into the aperture on a raised ridge as in Distorsio. Kotakaia simplex, with its strongly protruding basal columellar ridge, is clearly related more closely to Distorsio than to Personopsis, but its small size, regular coiling, and simple sculpture make the genus Kotakaia necessary for the Pitt Island species. The earliest undoubted Personopsis appears to be Eutritonium rutoti Vincent, 1930 (see particularly Krach 1963, p. 102, pi. 23, fig. 6) from the Montian (early Middle Paleocene, a little older than the Pitt Island fossils) of Europe; all other Personopsis species are from Eocene to Pliocene rocks, and in the living fauna of the Indo-West Pacific and Atlantic Oceans. Therefore, contrary to earlier assumptions (e.g., Pilsbry 1922, p. 357), Personopsis was not the ancestor of Distorsio.

Distribution: Waipawan, Red Bluff Tuff, "Rocky Side" bay, neck of Tarawhenua Peninsula, Pitt Island, Chatham Islands, uncommon; syntopic with Sassia n. sp. A (above) in a volcanic hard-ground environment.

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
ISBN 978-0-478-19705-1
ISSN 1177-2441
(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)


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