Abstract

This paper shows important positions of the Western Interior Cretaceous seaway. Shorelines are shown for 12 ammonite zones that range in age from the middle of the late Albian to the top of the early Maastrichtian. These zones, from oldest to youngest, are: Eopachydiscus marcianus (middle upper Albian), Neogastroplites americanus (lower Cenomanian), Conlinoceras tarrantense (lower middle Cenomanian), Collignoniceras woollgari (lower middle Turanian) , Prionocyclus hyatti (upper middle Turanian), Scaphites whitefield (upper Turonian), Clioscaphites vermiformis (middle Santonian), Scaphites hippocrepis (lower Campanian), Baculites obtusus (lower middle Campanian), Baculites scotti (upper middle Campanian), Baculites compressus (upper Campanian), and Baculites clinolobatus (lower Maastrichtian). Each time zone is shown on a map that includes the collection sites, geographic distribution of zonal fossils, and county lines for accurate reference.