The recognition and classification of trace fossils in carbonates of the Upper Ordovician Yeoman Formation in southeastern Saskatchewan are hindered by the complex diagenetic history of these rocks. Since many primary characteristics of deposits greatly influence diagenesis, the distinction between sedimentary and diagenetic fabrics can be difficult. This problem presents itself clearly in an examination of the trace fossils of the Yeoman Formation, which is characterized by conspicuous dolomite mottling. To date, it remains debatable whether these trace fossils represent Thalassinoides or sediment dolomitization around smaller, causative burrows. Most ichnological studies have been performed in clastics or chalks, and the methodology developed for these studies is difficult to apply to similar research in Paleozoic platform carbonates. The purpose of this paper is to describe the trace fossils of the Yeoman Formation, and to explore their potential usage in determining changes throughout the deposition of this thick platform carbonate sequence. In the examination of the biogenic sedimentary structures of the Yeoman Formation, nine discrete trace fossils are observed, many being part of composite burrow systems. Except for Trypanites, Trichophycus, and Palaeophycus, these trace fossils are indicative of feeding activities. Their diversity of form gives the impression of a diverse benthic fauna, but the relatively uniform diameter of the feeding burrows suggests that a small group of organisms may have been responsible for the various forms. These burrowing organisms shifted their feeding behaviours in response to changes in paleoenvironmental conditions, such as water energy, depth, oxygenation, and nutrient availability. The association of more complex feeding structures with the larger, vegetative-state, disseminated B Gloeocapsomorpha prisca alginite indicates that harsher conditions, which accompany the algal blooms, forced infauna to adapt their feeding behaviours.