The jaw muscles were studied in seven genera of macropodoid marsupials with diets ranging from mainly fungi in Potorous to grass in Macropus. Relative size, attachments, and lamination within the jaw adductor muscles varied between macropodoid species. Among macropodine species, the jaw adductor muscle proportions vary with feeding type. The relative mass of the masseter is roughly consistent, but grazers and mixedfeeders (Macropus and Lagostrophus) had relatively larger medial pterygoids and smaller temporalis muscles than the browsers (Dendrolagus, Dorcopsulus, and Setonix). Grazing macropods show similar jaw muscle proportions to ''ungulate-grinding" type placental mammals. The internal architecture of the jaw muscles also varies between grazing and browsing macropods, most significantly, the anatomy of the medial pterygoid muscle. Potoroines have distinctly different jaw muscle proportions to macropodines. The masseter muscle group, in particular, the superficial masseter is enlarged, while the temporalis group is relatively reduced. Lagostrophus fasciatus is anatomically distinct from other macropods with respect to its masticatory muscle anatomy, including enlarged superficial medial pterygoid and deep temporalis muscles, an anteriorly inflected masseteric process, and the shape of the mandibular condyle. The enlarged triangular pterygoid process of the sphenoid bone, in particular, is distinctive of Lagsotrophus. Anat Rec, 292:870-884, 2009. V V C 2009 Wiley-Liss, Inc.Key words: masticatory muscles; masseter; temporalis; kangaroo; Lagostrophus fasciatus Kangaroos, wallabies, and rat-kangaroos (superfamily Macropodoidea) are Australia's dominant mammalian herbivores. They vary markedly in dietary preferences, similar to the artiodactyl ungulates of other continents. Some species utilize many different foods, whereas others are much more specific in their choice of food items. Different foods require processing in different ways. Masticatory morphology represents a trade-off between what is required to effectively break down food and phylogenetic constraints. The correlation between feeding strategy and morphology in kangaroos has been investigated by several researchers, and the results have indicated differences in dental morphology and behavior