Not only do we have the fossilized remains of a crab (Dakoticancer sp.), we have coprolites! These tiny coprolite pellets are thought to have been left by segmented worms that fed on the little crab corpses.
Source: Gale A. Bishop did a study of discussing this subject in a paper entitled, "Pierre Feces: A Scatological Study of the Dakoticancer Assemblage, Pierre Shale (Upper Cretaceous) of South Dakota." This doubly interesting little crab was one of those collected as part of that study.