Article: Cenomanian micromorphic ammonites from the Western Interior of the USA

Calcareous concretions from middle and upper Cenomanian (Cretaceous) shale sequences in Montana and Wyoming yield, on rare occasions, abundant minute ammonites. Some are juveniles of large species, and give valuable evidence on early ontogeny and evolutionary affinities of these taxa. They provide evidence for the probable evolutionary origins of a series of hitherto undescribed progenic dwarf genera, adult at 4-5-16-5 mm diameter that are a remarkable feature of these assemblages. Five new genera, Kastanoceras, Alzadites, Microsulcatoceras, Cryptometoicoceras and Buccinammonites are introduced. 33 species are described from Montana, Wyoming, Utah, New Mexico and Texas; 16 are new, the others were previously unknown in the region or show new details of early ontogeny. New taxa are: Moremanoceras montanaense sp. nov.; Cunningtoniceras sp. juv.; Tarrantoceras exile sp. nov.; Kastanoceras spiniger gen. et sp. nov.; Alzadites alzadensis gen. et sp. nov.; A. westonensis gen. et sp. nov.; A. incomptus gen. et sp. nov.; Alzadites? sp.; Alzadites sp. A; Microsulcatoceras puzosiiforme gen. et sp. nov.; M. crassum gen. et sp. nov.; M. texanum gen. et sp. nov.; Microsulcatoceras sp.?; Cryptometoicoceras mite gen. et sp. nov.; Nannometoicoceras nanos sp. nov.; Nannometoicoceras ? glaber sp. nov.; Buccinammonites minimus gen. et sp. nov.; Idiohamites pulchellus sp. nov.; I. bispinosus sp. nov.; Carthaginites aquilonius sp. nov.; and Scaphites (Scaphites) sp.