No, a musky rat kangaroo is not a decomposer.
Decomposers break down dead organic matter. Musky rat kangaroos are herbivores, meaning they eat plants. They do not consume dead animals or decaying matter. They are primary consumers in the food chain. They consume plants, which are producers. Their role is important for the ecosystem because they play a role in dispersing seeds and maintaining the vegetation of their habitat.
Examples of decomposers include fungi, bacteria, and some insects like dung beetles.