The Greenhorn Limestone was deposited in the middle of the Upper Cretaceous Western Interior Seaway of North America. Based on materials collected from southeastern Nebraska, we report an assemblage of fossil marine fishes from the upper half (Jetmore and Pfeifer members) of the formation that represents the peak transgressive phase of the seaway. The ichthyofauna consists of at least ten taxa, including at least six chondrichthyans and four osteichthyans. The fish assemblage is small but includes durophagous, large predaceous, and medium-sized opportunistic sharks as well as small, medium-sized, and large bony fishes.