Ammonite 'Metengonoceras' Hyatt, 1903, from the Mowry Shale (Cretaceous) of Montana and Wyoming

摘要

Pseudoceratitic ammonites of the family Engonoceratidae are locally common in the Mowry Shale in the central and northern parts of the Western Interior of the United States. Most occurrences are of crushed, specifically indeterminate specimens, but occasional collections from concretions have well-preserved, uncrushed material. Metengonoceras aspenanum (Reeside and Weymouth) is revised on the basis of uncrushed specimens from a concretion in the Neogastroplites americanus zone in the Colorado Shale of Wheatland County, Montana. Metengonoceras aspenanum seems to be older than M. teigenense, n. sp., and both species are believed to be of early Cenomanian age.