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

Abstract

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.

Muscular anatomy of the forelimb of tiger (Panthera tigris)

“…The larger m. triceps brachii caput longum, and to a lesser extent caput laterale, in P. tigris and P. leo may reflect a greater emphasis on capturing larger prey while using the forelimbs to push the prey down on the ground before and during the killing bite. This is consistent with other studies that found that large-prey specialists tend to have larger forearm extensor muscles than small-prey specialists (Smith et al, 2021;Souza Junior et al, 2021).…”

“…Felidae are well‐known for being a morphologically conserved group and the forelimb musculature seems to follow that pattern (Cuff et al, 2016; Gonyea, 1976; Julik et al, 2012; Souza Junior et al, 2021). Although our dissection corroborates this general morphological conservatism, our results also demonstrate differences between tigers and other felids that are likely due to body size and prey size preference in large versus medium‐sized felid species, as well as phylogeny.…”

“…We averaged the muscle mass from the right and left sides and used those values to calculate total and regional muscle mass of the forelimb as well as proportional muscle mass for each TA B L E 1 Right, left, and average muscle mass (g) and proportional muscle mass (%) in our tiger specimen region and muscle (Table 1). For statistical analysis, we calculated the proportional mass of muscles grouped in two separate ways: by region, creating five regional variables, and by function, creating ten functional variables, which facilitated comparison with more felid taxa (Cuff et al, 2016;Hudson et al, 2011;Julik et al, 2012;Smith et al, 2021;Souza Junior et al, 2021;Souza Junior et al, 2018;Viranta et al, 2016). The functional groups follow the methods of Souza Junior et al (2018); the muscles within functional and regional groups are listed in Table 2.…”

Functional and phylogenetic interpretation of the forelimb myology of two South American carnivorans, the ring‐tailed coati (Nasua nasua) and crab‐eating raccoon (Procyon cancrivorus)

“…In both cases, manual dexterity and versatility is required, hence its intrinsic, and more specifically, the distal musculature tends to be well developed compared to the extrinsic one (i.e., larger mass values, larger area of origin or insertion). Conversely, runner and half‐bounding carnivorans tend to have a greater development of the proximal muscle masses in the thoracic limb, and particularly, the retractor muscles, to the detriment of the distal forearm musculature (Böhmer et al, 2018; Ercoli et al, 2015; De Souza Junior et al, 2021; Figure 12).…”

Functional Anatomy of the Thoracic Limb of the Komodo Dragon (Varanus komodoensis)

“…In the case of the pelvic limb of V. komodoensis , an increase in the muscle mass of the cross-sectional area of the key leg muscles was observed, which is correlated with the spreading posture, providing the opportunity to depart from the upright posture of giants [ 17 , 47 ]. Greater muscle mass in individual areas is associated with the need for organized manual skills of the animal, the versatility of movement (distal location), and the necessary traction (proximal location) [ 48 ].…”