Nautiles paléocènes du Niger

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• 作者：H. Tintant ; J. Lang ; B. Moussa ; K. Alzouma ; M. Dikouma
• 关键词：NAUTILOIDS ; PALEOCENE ; NIGER ; BIOSTRATIGRAPHY ; PALEOECOLOGY
• 刊名：Geobios
• 出版年：2001
• 出版时间：2001
• 年：2001
• 卷：34
• 期：6
• 页码：629-656
• 全文大小：9748 K

文摘

Large numbers of Tertiary nautiloids were collected from north-west (Mentès and Tillia), central (Kao) and southern (Malbaza) Niger. Study of them reveals two somewhat different fauna: a richer one from the central region (Kao) characterized by numerous specimens of Deltoidonautilus molli (Douvillé), and a poorer one characterized by Deltoidonautilus sudanensis and D. chudeaui from northern and southern regions alike. Judging from the associated fossils, the substantial differences between these Paleocene forms relate more to ecology than to age. Both apparently inhabited shallow, still-water environments despite the abundance of forms with highly folded suture lines (Deltoidonautilus), which were characteristic of deep marine environments in the Late Cretaceous. These forms seem to have adapted to shallower environments in the Paleocene without undergoing major morphological change, probably after the forms with slightly wavy suture lines that occupied this niche previously (Erutrephoceras and Cymatoceras) vanished at the end of the Cretaceous. Several new species are described, in particular a Cimomia whose widely flared aperture must have had periumbilical horns. Statistical study of the most common forms (Deltoidonautilus molli Douvillé and Cimomia nigerensis nov.) shows great variation in width, possibily indicative of slight probably sexual dimorphism, comparable with that of present-day Nautilus.