104 - Head and Neck Musculature of the Snow Leopard, Panthera Uncia

Poster Board Number: 104
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Abstract Body : Snow leopards (Panthera uncia) are the smallest member of their genus, which includes the lion (P. leo), jaguar (P. onca), leopard (P. pardus), and tiger (P. tigris, the largest congener and closest living sister-taxon of P. uncia). Due to its unusual vocalizations, prior anatomical head and neck studies of P. uncia focused on the larynx and hyoid apparatus. Hence, there are no recent studies detailing the head and neck anatomy of P. uncia that could inform clinical, conservation, and evolutionary studies. The aim of our study is to document the head and neck muscular anatomy of the snow leopard and to compare these data to published accounts of other felids.
We dissected, mapped, measured, and imaged the head and neck musculature of two adult P. uncia specimens (1M/1F; mass range for species: M, 45-55 kg; F, 35-40 kg). The musculature from the following regions were described and assessed: hyoid, laryngeal, muscles of facial expression, muscles of mastication, extrinsic and intrinsic ear muscles, tongue, and pharynx. Length and mass of each muscle were recorded using calipers and a digital balance. Muscle masses of both the male and female were compared to each other to assess sexual size dimorphism. Muscle mass data were also compared to published data on the Sumatran tiger (P. tigris sumatrae; F, 152 kg) and serval (Leptailurus serval; M, 9.7 kg) for general head and neck muscles. Masticatory muscles were compared across felids (pantherines and felines), as there is a larger available comparative sample for this functional muscle group. Individual muscle masses were regressed against log body mass. Differences between the two subfamilies, Pantherinae and Felinae, were assessed using Kruskal-Wallis tests for individual muscle masses. Physiological Cross-Sectional Area (PCSA) of the masticatory muscles was calculated and compared. No comparative muscle length data were available.
Evidence of size sexual dimorphism in the snow leopards was not readily apparent. The female specimen had absolutely larger muscles than the male in numerous cases, possibly due to the advanced age of the male specimen. The anatomy of the head and neck musculature of the snow leopard shows similarities with P. tigris with some differences in both muscles of facial expression and mastication. P. uncia had a lower relative masticatory muscle mass than the mean of the comparative felid sample, including a relatively smaller m. temporalis. The Regression Analysis of PCSA for masticatory muscles against log body mass indicated that P. uncia falls slightly below the regression line, but still within the 95% confidence interval for other comparative felid taxa.

This study represents the most complete documentation of head and neck muscular anatomy for any pantherine. Solitary hunters, snow leopards are known to prefer ungulate prey that are as large or larger than themselves. They are also known to have one of the largest mouth gapes among all carnivorans (>70◦), but with the weakest bite force. Our analyses indicate that P. uncia has less massive masticatory muscles, which likely reflects this weaker bite force. The muscles responsible for opening the mouth are quite long in P. uncia (m. digastricus anterior and posterior combined length of 136.69 mm and m. pterygoideus lateralis, 49.04 mm). These elongated muscles are indicative of the wide gape, necessary for the killing bite on the throats of larger ungulates.