The extrinsic and intrinsic forelimb musculature of the lesser grison (Galictis cuja), a short-legged mustelid of southern South America, is studied for the first time. We present descriptions, muscular maps, and weight data. Muscular anatomy description of the lesser grison provides the framework for discussing the myological diversity of mustelids and other caniforms, for addressing nomenclatural problems (such as synonymy and homonymy), and for highlighting some functional and phylogenetically informative traits. We recognize in the lesser grison features shared by all mustelid species, and some other caniforms, especially mephitids, such as the presence of rhomboideus profundus, an angular head of triceps brachii, and, apparently, the absence of a flexor digitorum brevis manus. An unexpected record of articularis humeri, a proximal origin of the brachioradialis, and the absence of the tensor fascia antebrachii are recorded for this species. As other ictonychines and mustelines, Galictis cuja possesses stronger and subdivided protractors and sagittal rotators of the forelimbs, as well as shoulder and elbow extensors. These features allow for resistance in landing during bounds and increase the stride length during epigean and subterranean crouched locomotion. Powerful neck musculature assists during hunting and carrying of prey. Weakness of some retractors and intrinsic flexors is related to a relatively minor importance of the forelimbs as propellers during bounding and the lack of other specializations. The configuration of the rhomboideus and the absence of coracobrachialis seem to be informative at the subfamiliar level within Mustelidae. The comprehensive and comparative review of available information leads us to propose possible solutions to old nomenclatural problems and of identification. This allows us to reassess of some myological features as diagnostic of caniform clades.

We analysed mandible shape of the orders Dasyuromorpha, Didelphimorphia, and Carnivora using twodimensional geometric morphometrics, in order to explore the relationship between shape, size, and phylogeny. We studied 541 specimens, covering most of the genera of the terrestrial Carnivora (115 species) and a wide sample of marsupials (36 species). The observed shape variation had an ecological component. As an example, omnivorous carnivores have thick mandibles and large talonids in the carnassials, while hypercarnivores possess short mandibles and reduced talonids. There is also a discrimination between different taxonomic groups (i.e. marsupials and Carnivora), indicating some kind of constraint. Size explains a large percentage of total variance (large species had shorter and stronger mandibles, with anteriorly displaced carnassials), was significant when phylogeny was taken into account with a comparative method, but not when size and shape were optimized on the phylogeny. Carnivora presents a larger disparity and variation in body size, which could be related to the difference in teeth replacement. The optimization of mandible shape on the phylogenetic tree indicates that functional aspects, such as diet, are a key factor in the evolution of the carnivore mandible, but also that there is a phylogenetic pattern that cannot be explained by differences in diet alone.

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