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Internal structures in the early whorls of Mesozoic ammonites. American Museum novitates ; no. 2823

Show simple item record Landman, Neil H. en_US Bandel, Klaus. en_US 2005-10-06T18:10:44Z 2005-10-06T18:10:44Z 1985 en_US
dc.description 21 p. : ill. ; 26 cm. en_US
dc.description Includes bibliographical references (p. 21). en_US
dc.description.abstract "The first few septa and associated structures in the early whorls of Mesozoic ammonites were studied in a number of genera including Quenstedtoceras, Kosmoceras, Euhoplites, Hypacanthoplites, Baculites, and Scaphites and its related genera. Exceptionally well-preserved specimens with little obscuring matrix inside permitted observations of the spatial arrangement of the first few septa and were supplemented by sections polished parallel to the median plane. Our observations indicate that: 1. The proseptum is a single structure and does not consist of two septa. Prismatic attachment deposits of the caecum and siphuncle occur around the proseptal opening. 2. In all genera except Quenstedtoceras, the second septum is moderately distant from the proseptum and, in median section, is slightly convex, not concave, toward the aperture. In Quenstedtoceras, however, the second septum grows dorsally into the proseptum and is only conspicuous on the venter. These relationships are also expressed in the shape and spacing of the corresponding sutures on steinkerns of the initial whorls. 3. In all genera in which the original shell structure was preserved, the second septum is nacreous, not prismatic. Therefore, in agreement with Drushchits and Khiami (1970), we prefer the simpler terms second septum and third septum for primary septum and nacroseptum, respectively. 4. The development of a prismatic attachment ridge at the base of the proseptum, dorsal muscle scars just adoral of each septum, and wrinkles in the proseptum and prosiphonal attachment sheets support the model of early ammonite ontogeny proposed by Bandel (1982)"--P. [1]. en_US
dc.format.extent 12703949 bytes
dc.format.mimetype application/pdf
dc.language eng en_US
dc.language.iso en_US
dc.publisher New York, N.Y. : American Museum of Natural History en_US
dc.relation.ispartofseries American Museum novitates ; no. 2823 en_US
dc.subject.lcc QL1 .A436 no.2823, 1985 en_US
dc.subject.lcsh Ammonoidea. en_US
dc.subject.lcsh Mollusks, Fossil. en_US
dc.subject.lcsh Paleontology -- Mesozoic. en_US
dc.title Internal structures in the early whorls of Mesozoic ammonites. American Museum novitates ; no. 2823 en_US
dc.title.alternative Mesozoic ammonites en_US
dc.type text en_US

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  • American Museum Novitates
    Novitates (Latin for "new acquaintances"), published continuously and numbered consecutively since 1921, are short papers that contain descriptions of new forms and reports in zoology, paleontology, and geology. New numbers are published at irregular intervals.

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