[Extract] A survey of over 50 localities for invertebrate fossils and their traces in the mudstones and sandstones of the Kaiparowits Formation, which spans 1.8 million years of Late Cretaceous (Campanian) time, demonstrates that it is one of the most prolific units in the Western Interior. Pulmonates, caenogastropods, and freshwater bivalves dominate the invertebrate fossil record both in number and diversity, and these are accompanied by ostracodes and a unique occurrence of bryozoan. Trace fossils such as the type specimens of Socialites nests and Osteocallis bone scrapings strongly suggest the activity of insects despite their absence in the body fossil record. At least 35 different aquatic and terrestrial gastropod and 13 freshwater bivalve morphotypes described from the formation support other independent evidence that the Campanian of southern Utah had a warm, humid climate with perennial aquatic environments. The highest-quality autochthonous preservation, including primary aragonite shell, occurs in facies interpreted as overbank ponds, lakes, and marshes. The greatest local diversity of 20 aquatic mollusk and one brackish-water bryozoan taxa is reported from a thick shell conglomerate that is interpreted as a mass-mortality storm deposit. Maximum diversity of mollusks in the middle of the formation appears to coincide with an increase in facies recording wetter Auvial environments, but future collecting efforts are required to isolate this relationship from taphonomic or sampling biases that may contribute to this preliminmy signall
