The Okpikruak formation of Berriasian to Valanginian age in many places contains an abundance of the pelecypod Aucella, but otherwise contains very few fossils. The Aucellas belong to species that are common in the Boreal region and along the west coast of North America. They premit dividing the Okpikruak formation into three faunal zones based on the stratigraphic distibution of the species. The thick shells of the Aucellas and their common occurrence in coarse detrital sedimentary beds suggest that they lived in the shallowest part of the neritic zone or even partly in the littoral zone.

The beds of Albian age in northern Alaska include more genera and species of marine megafossils than have ever been described previously from Albian beds in lands bordering the Arctic Ocean. Most of the fossils are from beds that are dated as middle Albian. A scarcity of megafossils in the lower Albian beds coincides with a scarcity of microfossils and is ascribed to exceedingly rapid sedimentation. A scarcity of marine megafossils in the latest Albian beds is explained by the fact that part of these beds are continental and much of the remainder are littoral in origin. The Albian sedimentary rocks are divided on the basis of megafossils into 5 faunal zone, of which 3 are of early Albian age, 1 is of middle Albian age, and 1 is probably of late Albian age. The general composition of the megafossil assemblage living in, or on the bottom of the Albian sea in northern Alaska greatly resembles assemblages living today in shallow sea bottoms of temperate latitudes.

The pelecypod Aucella, of latest Jurassic and earliest Cretaceous age, has been subdivided into more than a hundred species on the basis of mirnor differences without allowing for biological variation, or for variation due to crowding that is normal for an attached gregarious pelecypod. As a result, in any large collection from a single locality, specimens can be selected that fit the definitions of a number of species and yet these so-called species are connected by many specimens showing transitional characteristics. Such an assocition appears, therefore, to represent a single variable population. If the species of Aucella are defined making allowance for variation, the number of species is greatly reduced, but the specific concepts can be grasped readily by geologists and used for mapping purposes. Seven zones based on species of Aucella can now be recognized easily in the field in North America, as has been demonstrated by geologists of the U.S. Geological Survey.