Evolutionary history or function? Which preponderates in the expression of the muscle mass of the thoracic limb in wild carnivorans?

Thoracic limbs are extremely versatile and exhibit informative characteristics about habits of the Carnivora order in the wild. Despite this relevance, comparative studies with quantitative variables on thoracic limb muscles are still scarce in carnivorans. The aims of this study were to measure the mass of the intrinsic muscles of the thoracic limb of neotropical species of the Carnivora order and to establish comparative conjectures. For this purpose, 39 thoracic limbs of 10 neotropical carnivorans species were dissected. The mass of each muscle was measured on a digital scale, muscles were grouped by function, and the mass average percentage that each functional group of muscles occupied in the thoracic limb was calculated. The data of the present study was added to that available in the literature for 22 other carnivoran species. Three groups of species were considered: Canidae, Musteloidea, and Feliformia. Comparatively, the eight canid species included in this analyses concentrate muscle mass proximally in the thoracic limb to prioritize essential cursoriality. The nine musteloids had more muscle mass in the distal muscles due to the demand for versatility and manual strength, and the 14 Feliformia species exhibited an intermediate trend. The analysis of clusters revealed a great overlap of the percentage distribution of muscle mass with the phylogeny previously established for carnivorans. It could be verified that the distribution of muscle masses meets the demand of the locomotor habits of the species up to a certain level, from which phylogeny begins to limit morphological adaptations.