Sexual Dimorphism and Adaptations in the Forelimb of the Snow Leopard ( Panthera uncia )

Abstract

Snow leopards (Panthera uncia) are notoriously difficult to research and classified as vulnerable by the IUCN. There are only 5,000 mature individuals left inhabiting the rugged terrains of Afghanistan, China, Mongolia, and Uzbekistan. P. uncia is unique compared to other felids because it lives in harsh winter climates, attacks by pouncing from above, and scales great steep slopes in the snow instead of hunting in packs or across long distances. In this study, two specimens of P. uncia (1M/1F) were dissected, and their forelimb myology thoroughly documented. Findings revealed notable, sexually dimorphic and functional differences in the forelimb of P. uncia compared to other pantherine felids. Male snow leopards generally exhibit greater bone mass and more extensive muscle attachments, useful for male-male competition and other situations of increased aggression. Despite the larger body mass of our P. uncia male specimen (39 kg vs. 36 kg), most of the forelimb muscle masses of the male were comparable to the female, indicating that his forelimb muscles were relatively smaller for his body size. In the male, m. rhomboideus pars cervicalis was stouter and more robust than m. rhomboideus pars thoracis, and had an expanded origin compared to the female. This difference could allow for more powerful scapular retraction during grappling with prey or an adversary. M. triceps brachii caput longum and laterale was longer in the male, resulting in a stronger lever for extension of the elbow. The seven subdivisions of mm. pectorales in the male were organized from superficial to deep, versus eight subdivisions arranged from cranial to caudal in the female. The mm. pectorales of the male did not insert onto the lesser tubercle of the humerus, and the muscles bellies exhibited less fusion. The pectoral and scapular musculature of P. uncia are enlarged compared to other pantherines. This morphology likely provides extra forelimb power and stability for climbing steep terrains. Muscle pectoralis profundus of P. uncia is substantially larger than in other felids with five bellies, and only one belly was observed for m. pectoralis superficialis. This configuration may be helpful for climbing and pouncing. P. uncia was found to possess a diminutive bony clavicle, which may provide stability to the forelimb. M. brachialis had three bellies and fused with m. cleidobrachialis, and the m. biceps brachii tendon of insertion bifurcated to attach on both the ulna and radial tuberosity. All bellies of mm. brachialis, pectoralis superficialis, and cleidobrachialis attached to the lateral bifurcation of the m. biceps brachii tendon. Additional muscular heads and insertions around the elbow provide stability and leverage to the joint. This morphology suggests a greater need for power and stability in the forelimbs of P. uncia and may help with scaling through rugged terrain and manipulation of prey. Intrinsic manus muscles are enlarged, forming a widened surface area to distribute body weight while walking on soft snow.