Description of two species of Hoploscaphites (Ammonoidea, Ancyloceratina) from the Upper Cretaceous (Lower Maastrichtian) of the U.S. Western Interior. (Bulletin of the American Museum of Natural History, no. 427)

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Date

2019-02-22

Journal Title

Journal ISSN

Volume Title

Publisher

American Museum of Natural History.

DOI

DOI

Abstract

Two species of scaphitid ammonites (Ammonoidea: Ancyloceratina) from the Upper Cretaceous (lower Maastrichtian) of the Western Interior of North America are described. Hoploscaphites macer, n. sp., is medium size, with coarse ribs on the phragmocone, which become finer on the body chamber, and closely spaced ventrolateral tubercles. It occurs in the upper part of the Baculites baculus Zone and lower part of the overlying B. grandis Zone in the Pierre Shale in Montana, Wyoming, and Colorado, and in the Bearpaw Shale in Montana. Hoploscaphites criptonodosus (Riccardi, 1983) is larger and more coarsely ornamented, including one or two rows of lateral tubercles on the flanks of the phragmocone. It occurs in the upper part of the Baculites baculus Zone and overlying B. grandis Zone in the Pierre Shale in Montana, Wyoming, Colorado, and possibly South Dakota, and in the Bearpaw Shale in Montana and Saskatchewan, Canada. Both species form part of an evolving lineage of Hoploscaphites that first appears in the Western Interior of North America in the middle Campanian.

Description

72 pages : illustrations (some color), map ; 26 cm.

Keywords

Hoploscaphites macer., Hoploscaphites criptonodosus., Ammonoidea., Pierre Shale., Bearpaw Formation., Great Plains., West (U.S.), Saskatchewan.

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