Appendicular myology of the hadrosaurian dinosaur Maiasaura peeblesorum from the Late Cretaceous (Campanian) of Montana

Musculature of the pectoral and pelvic appendages and girdles of adult and nestling Maiasaura peeblesorum (Dinosauria: Ornithischia: Hadrosauridae) from the Late Cretaceous of Montana is restored according to a phylogenetically based methodology. This methodology uses an explicit, independently derived phylogenetic hypothesis of the fossil taxon and related extant taxa to generate a series of inferences regarding the presence of a muscle, its number of components, and the origin(s) and insertion(s) of these components. Corroborative osteological evidence is sought on the fossil in the form of scars and processes that fulfill the criteria for muscular attachment according to generalisations based upon extant vertebrates. A total of 46 muscles are restored, although separate attachment sites for numerous muscles cannot be discerned on the fossils. Osteological evidence for several muscles can be found in nestlings of Maiasaura despite their skeletal immaturity. Results of the phylogenetically based approach and new hypotheses for homologies of deep dorsal thigh muscles suggest that it is more parsimonious to restore the femoral insertions of M. iliofemoralis on the greater trochanter and M. puboischiofemoralis internus on the anterior (lesser) trochanter, a reversal of the traditional interpretation. The often-cited osteological specialisations of birds for flight are not accompanied in all instances by profound myological transformations, and birds must be included in any attempt to restore the myology of extinct dinosaurs.