Comparative Jaw Muscle Anatomy in Kangaroos, Wallabies, and Rat‐Kangaroos (Marsupialia: Macropodoidea)

Abstract

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

Three dimensional digital reconstruction of the jaw adductor musculature of the extinct marsupial giantDiprotodon optatum

“…4 and 5) based on dissections of living marsupials conducted for this study and published dissections of wombats (Crompton et al, 2008; Murray, 1998), koalas (Davison & Young, 1990) and kangaroos (Abbie, 1939; Tomo et al, 2007; Warburton, 2009). The masseter muscle group is the largest jaw muscle calculated for Diprotodon , accounting for 44 percent of the total jaw muscle mass (Table 1).…”

“…This is indicated by moderately developed frontal crests that extend beyond the fronto-parietal suture and converge at the dorsal midline. From previous descriptions of the muscle in modern marsupials (Crompton et al, 2008; Davison & Young, 1990; Tomo et al, 2007; Warburton, 2009), and from additional dissections, the temporalis was reconstructed as two parts: the superficial lateral part (m.Ts) and the deep medial part (m.Tp), following (Warburton, 2009). The smaller lateral portion of the temporalis originates from the postero-medial portion of the zygomatic arch and squamosal bone, and inserts to the superior-lateral border of the coronoid process of the mandible.…”

“…The terminology used here was selected for its consistency with jaw muscle nomenclature used for marsupials (Abbie, 1939; Crompton et al, 2008; Davison & Young, 1990; Murray, 1998; Tomo et al, 2007; Turnbull, 1970; Warburton, 2009). The masseter muscle group includes three portions (superficial, deep and zygomaticomandibularis) based on their area of origin.…”

“…The jaw adductor musculature of Diprotodon was reconstructed using data from dissections of modern wombats, koalas and kangaroos, MRI scans of a wombat and koala, and previously published dissections (Crompton et al, 2008; Davison & Young, 1990; Murray, 1998; Tomo et al, 2007; Warburton, 2009). This allowed the reconstruction of the complex muscle anatomy by assessing the locations of muscle attachment sites, muscle volume and identifying muscle orientations.…”

Revision of Oligo-Miocene kangaroos, Ganawamaya and Nambaroo (Marsupialia: Macropodiformes, Balbaridae)

“…There is a distinct, well-developed sulcus on the anterior extremity of the zygomatic arch. This sulcus appears to be related to the attachment of the superficial masseter muscle (Warburton, 2009). As in other balbarids, the zygomatic arch transitions smoothly into the facial region as opposed to being separated by a sulcus.…”