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We describe three species of large scaphitid ammonites (Ammonoidea: Ancyloceratina) from the Upper Cretaceous (upper Campanian–lower Maastrichtian) of the Western Interior of North America. Each species occurs as two dimorphs, referred to as macroconch and microconch. All three species share a similar pattern of ornamentation consisting of long, thin, nonbifurcating ribs on the adoral part of the phragmocone, suggesting that they constitute a single monophyletic clade. Macroconchs of Hoploscaphites crassus (Coryell and Salmon, 1934) are characterized by a globose whorl section, with closely spaced ventrolateral tubercles on the body chamber, usually persisting to the aperture. Macroconchs of Hoploscaphites plenus (Meek and Hayden, 1860) differ from those of H. crassus in having a more subquadrate whorl section with flatter flanks, and fewer, larger, and more widely spaced ventrolateral tubercles. Macroconchs of Hoploscaphites peterseni, n. sp., closely resemble those of H. crassus, but differ in being nearly circular in side view with a more compressed whorl section. All three species lived at approximately the same time in the same general area and depositional environment. They are abundant in the Baculites baculus Zone but also occasionally occur in the B. eliasi Zone and possibly lower part of the B. grandis Zone. They are present in the Pierre Shale of east-central Montana and east-central Wyoming, the Lewis Shale of south-central Wyoming, and the Bearpaw Shale of northeast Montana. It is possible that these three species represent subspecies within a single species or a “flock” of very closely related species, similar to the “species flocks” observed in modern cichlid fishes.

The stratigraphic context and geochemical proxy potential are described for a newly reported early Jurassic marine iron ooid deposit in west central Nevada, U.S.A. Sedimentary analysis of the Ferguson Hill Member in the Sinemurian-aged Sunrise Formation was conducted in the Gabbs Valley Range of Nevada, U.S.A. Iron ooids were examined by transmitted light microscopy and electron scanning microscopy and found to consist of chamosite/berthierine and amorphous silica in cortical layers of the Sunrise Formation. Sedimentological characteristics of the uppermost beds of the Ferguson Hill Member show iron ooids are associated with transgressive deposits on the earliest-known first post-extinction metazoan carbonate factory identified in Eastern Panthalassa. The Ferguson Hill Member iron ooids are unique among most iron ooid deposits for being distributed grains within the carbonate. The formation of such a deposit required concentrations of iron and silica and fluctuating oxidation/reduction conditions sufficient to produce chamosite/berthierine and silica while not completely shutting down the shallow marine carbonate factory. For this reason, iron ooids observed in shallow carbonate sections serve as a useful indicator of shallow water geochemical conditions in the sedimentary record.