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A single chamber
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Pseudorthocerida
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Some of the most exciting finds to be made in the Reefton Formation are these specimens. They are orthocones (Pseuodorthocerida) - the shells of a straight Nautiloid. These are rare finds, for few discoveries have previously been reported from Devonian rocks in New Zealand. They thus merit further study. Key features of the specimens are the almost straight (slightly sinusoidal) body of the shell, which diminishes relatively rapidly at first from 15 mm to 12 mm in diameter then tapers more slowly. Individual chambers are ca. 8 mm in length. The chambers are distinctive with a slightly off-centre siphuncle (the small 'button'shaped feature).
Identification to genus or species level is nevertheless difficult. No material is available with which to compare the specimen, and descriptions of orthocones from elsewhere are also limited, and detailed illustrations of features, such as the individual chambers, seem to be lacking. Cocks and Cooper (2004), however, note a small orthocone fragment (two chambers long) from late Ordovician rocks in the Wangapeka Valley, which they tentatively assign to Holopea sp.. This species extended into the Devonian, so is one candidate. It's also known that the Reefton Formation was coterminous with SE Australia at the time of deposition, and is believed to be the equivalent of Emsian stage strata in Tasmania and Victoria. From that area, Teichert and Glenister (1952) note two genera - Dolorthoceras and Buchanoceras - and the latter of these is illustrated. The similarities to the long-section shown below are superficial but intriguing, so Buchanoceras provides a second possible identification. As yet, however, no identification can be suggested with any degree of confidence.
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Section of Orthocone in rock sample, showing chambers
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