Muscular anatomy of the forelimb of Leopardus geoffroyi: Functional and phylogenetic aspects in Feliformia, part I. Proximal forelimb

Anatomical knowledge is fundamental for all species. In particular, myology allows a deeper understanding of ecomorphology-especially for those species hard to observe in the wild-and may be an important source for phylogenetic information. In this study, we analyzed the myological variation of the musculature of the shoulder and arm of the forelimb in species of the suborder Feliformia and its relationship with the phylogenetic history and the locomotor behavior, habitat, and predatory habits of the species within this group, using Leopardus geoffroyi as a case study. We used gross-anatomy dissections of the shoulder and arm of three specimens of L. geoffroyi and contrasted these results to other previously described feliform species. Additionally, we optimized 15 myological characters to search for phylogenetic patterns. We present the first description and the first complete muscular maps of the forelimb shoulder and upper arm of L. geoffroyi. A small number of muscular characteristics allow L. geoffroyi to be distinguished from other feliforms, such as a possible partial division of m. biceps brachii, although they did not relate to any analyzed ecological habit. Some myological characteristics studied in this work contribute to the knowledge of the phylogenetic relationships and the morphological evolution of Feliformia. Felids are the only feliforms with a constantly present m. pectoantebrachialis (although it has been reported in some caniforms). Muscle rhomboideus capitis is present only in Felidae and Herpestidae, resembling various caniforms. Its presence could indicate a retention linked to their carnivoran ancestry. The Felidae and Hyaenidae represent two quite conservative morphotypes, as they present particular muscular configurations compared to other feliform families, but also, relatively little variation within each family. Functionally, some myological characters recorded in hyenids, L. lynx, P. uncia, A. jubatus (e.g., radio-ulnar insertion of m. biceps brachii), distinguish them from the rest of the species of the same suborder or family, and are convergent with other carnivorans with cursorial habits (e.g., canids). The functional and evolutionary analysis of the myology of the forelimb of L. geoffroyi and the different species of the suborder Feliformia allowed a better understanding of how muscle configurations reflect functional specialization to different ways of life. The muscle maps presented here, being the first available for a small Neotropical felid, can be considered a valuable source of information, useful for future studies of comparative anatomy in neontological and paleobiological contexts.

Functional myology of the thoracic limb in Pampas fox (Lycalopex gymnocercus): a descriptive and comparative analysis

The characteristics of the muscles of the thoracic limb were evaluated in 22 specimens of Lycalopex gymnocercus. Descriptive and comparative analyses showed similarity with other canids in terms of topography and tendon insertions. Differences with the domestic dog were observed in the pectoralis profundus, triceps brachii and interflexorii muscles. Intraspecific variations were observed in the rhomboideus capitis, serratus ventralis cervicis, extensor carpi radialis, extensor digiti I and II, lumbricales, flexor digiti I brevis, abductor digiti I brevis, and flexor digiti V muscles. The analyses of muscle architecture carried out in nine specimens showed that there was no difference in muscle percentage mass in the thoracic limb of males and females, but a young specimen showed significant lower percentage mass. The triceps brachii caput longus muscle showed the greatest mass, the subscapularis muscle showed the greatest physiological cross-sectional area value, and the extrinsic muscles, in general, presented the longest fascicles and higher architectural indexes. Muscle architecture data were compatible with those of a thoracic limb adapted to fast cursorial locomotion that prioritizes movements in a sagittal plane instead of rotation or adduction/abduction. There was a high association between functional percentage mass of the muscles in the thoracic limb and phylogeny in the Carnivora order. It may be inferred that carnivoran muscle mass is largely determined by phylogeny.