Anatomy of the Snow Leopard

The beauty of biological sciences is in its integration with other disciplines such as arts, anthropology, psychology and history. Anatomy, being among the major sub-disciplines of science, finds its usefulness in part in medicine, visual and performance arts, athletics, and in part in understanding ethnography and the science of mind and behavior. Anatomical study of species has been key to understanding the structure-functional relationships that makes each individual perfectly suited to their niche. The universe offers a plethora of diverse species, and studying the anatomy of each has led to innovations within and outside of science.

The snow leopard (Panthera uncia), perhaps the least talked about felid, is rather uniquely built and proposes some wonderful innovations with its anatomy that could be incorporated in life outside of biology. Over the years, there has been multiple literature publications on the morphology of each organ system of the snow leopard, albeit vulnerable to global extinction. The International Union for Conservation of Nature (IUCN) lists that there are about 2,710-3,386 mature snow leopards in its last assessment on November 2016, and the number is progressively decreasing (IUCN 2016). Found in mountain ranges and snowy alpine and subalpine regions of Asia, its stocky body, thick fur and padded paws are among its several adaptations for living in the cold (Sanquist and Sanquist 2002, 378). The snow leopard has a well-engineered body, robust bones, modified brain and nocturnal vision, all of which makes it an active hunter (Johansson et al. 2015). Findings from the morphological study of each of its organ systems can be incorporated into innovations in biotechnology, athletics, aerospace engineering and performance arts. Studying its anatomical adaptations can be extrapolated to applications in developing bionic eyes, aerospace landing, manufacture of protective sports gear and ballerina pointe shoes.

Members of the Felidae family have a large bulbus oculi (globe of the eye) relative to the size of their brain and a much larger retina (Snow et al. 2004). Having a large eye with large pupil allows for greater reception of incoming light. In the retina, rod cells are responsible for transmitting stimulatory signals to the visual cortex of the brain that allows animals to see dim light with low acuity. The retina in nocturnal mammals have more rod cells than cone cells that need higher intensity photons to transmit an impulse. Additionally, the heterochromatin in rod cells are placed in the center of the nucleus as opposed to the periphery in diurnal animals. Such inversion of chromatin placement focuses and directs light into the right sensitive regions of rod cells, allowing for better vision in extremely low light. Besides, presence of the tapetum lucidium membrane ensures that light that has not been absorbed by the rods and cones to be sent back to the photosensitive cells to be absorbed again (Reid 2009). Macular degeneration of the retina is a disease where the light sensitive part of the eye is damaged and is unable to transmit electrochemical signals. The signal is therefore not received by the brain, resulting in the failure to form a complete image. Patients with this disorder has to resort to corrective surgery which is highly invasive and risky. The National Vision Research Institute has recently launched the bionic eye that can correct vision in patients with macular degeneration or damaged photosensitive cells. A micro neuro-stimulatory chip measuring 2x4 mm is planted to the patient’s retina that mimic signal transduction similar to rods and cone cells. The system consists of a camera that is attached to a pair of glasses that transmit high-frequency radio signal to the chip. Electrodes in the chip transmit impulses to the optic nerve into the occipital lobe, by virtue of which an image is interpreted (Tsong 2007). Reflecting the engineering sophistication in the snow leopard’s retina, the quality of image and low light visibility in these bionic eye models can be enhanced. Felids have around 350,000 rod cells per mm2 of retina compared to 80,000-150,000 in humans. Each neuron pools signal from 1500 rod cells in felids, attributing to their nocturnal ability (Smith et al. 1987). Incorporating this into the engineering of the eye, the neuro-stimulatory chips can be modified to have a higher proportion of rod mimicking electrodes. The only set back is that vision acuity will be compromised, however, some adjustments can be made to solve the problem. As previously discussed, presence of tapetum membrane can redirect unabsorbed light back to the retina. The glasses can be modified to have a synthetic membrane similar to the tapetum that can be placed by the user in low light conditions. Therefore, a combination of higher rod cells mimicking electrodes and synthetic tapetum membrane can effectively improve the bionic eye technology.

The integumentary system of the snow leopard is unique in the sense that it has specialized adaptations to the base of its paws called foot pads. These pads are lined by densely cornified epidermis with papillary bodies that allows them to withstand high mechanical force. The subdermal layer is packed with cushions that are composed of collagen, reticular and elastin fibers along with clusters of adipose tissue that give these pads a spongy resemblance, acting as a shock absorber to mechanical stress (Ari et al. 2018). The same design is orchestrated in aerospace engineering to attenuate the impact of landing in spacecraft seats. The landing phase of aircrafts can be potentially dangerous to astronauts because of high impact loads that is transferred to the seats when the spacecraft reaches the ground. The Chinese Journal of Aeronautics published a paper that illustrates the current mechanisms of impact attenuation: a multi-direction attenuator where the seat is programmed to move in different directions upon landing to dissipate impact from collision and a vertical attenuator where the seat springs vertically to absorb the impact, much like suspensions in a car (Yu et al. 2015). The impact attenuation technology of felids inspired these scientists to design the spacecraft seats with energy absorbing materials like natural fibers and biomaterial foams to absorb energy into the seats during impact. The researchers took high speed photographs of different felid species landing from considerable height. Their forelimbs hit the ground first, causing them to compress their upper body, followed by landing of the hind limbs, forming an arched back. Using this motion capturing system, they programmed their seats to propel the foot point of the seat towards the ground first, followed by elevation of the head rest towards the axis and finally directing the head rest point of the seat towards the ground, resulting in absorbance of maximum impact load (Yu et al. 2015). Therefore, impact attenuation is possible by combining the idea of adaptive nature of felid landing on cushioned foot pads, and load distribution with their unique multi-impact landing.

The usefulness of foot pad technology in felids go beyond biology and engineering into performance arts. In ballet dancing, ballerinas usually wear leather or canvas pointe shoes that are made with tough yet flexible material so that they can bear weight on their toes and perform plantar flexion and extension in different dance moves. A study by Hanyang University Department of Rehabilitation medicine in Korea concluded that the highest pressure point in ballerinas are the heel and the great toe (Jhung et al. 2002). The study emphasized the importance of protective ballet shoes, however, the options are limited due to limited ongoing research in the area. In a separate study, the impact of pointe shoes on foot comport was evaluated. 14 out of 15 ballerinas participating the study admitted to using toe pads, lamb wool and/or gel toe spacers in their shoes to protect their feet from serious injuries (Xu 2016, 50). The morphology of foot pads, as described above, can serve as a potential solution to this rather unattended problem. Silicon padding inside ballet flats can resemble the adipose tissue layer in felid foot pads that absorbs shock on landing. The outer, touch layer provides friction which can reduce chance of slip and fall during complex dance maneuvers. A study by The Royal Society of Mathematical, Physical and Engineering Sciences simulated with cells made of hyper elastic materials containing gel filling. Mihai, Alayyash and Goriely (2015) studied tension and compression forces on this model to identify changes in elastic modulus with promising results. They concluded that the stiffness of the cell walls was undisturbed with low and small strain with the presence of incompressible cushions. A change in elastic modulus was appreciated only with very high strain.

Finally, the unique skeletal anatomy of skeletal system of snow leopards that enables them to be quick and run over 80 km/h has promising possibilities to set a foundation in improving athletes’ performances in various sports. Most Felidae species have a short pubic symphysis and ischium, along with narrow iliac crest that gives them greater range of motion of the torso and allows them to swiftly change directions without having to stop (Martin-Serra et al. 2015). Most contact sports including football and hockey mandates players to wear protective gear during play. It’s particularly important that players protect their hip bones since we have a wide iliac crest that protrudes laterally from the midline and can be prone to coming in contact with other players causing injury. One of the top sports protective gear manufacturers of the nation, Under Armour ®, makes polyester based pads with meshed padding to protect the pelvic girdle for football players. According to their official website, these 10 mm thick girdle pads are composed of 79% polyester and 21% elastane with the mesh panels consisting of 87% polyester and 13% elastane (Under Armour US 2018). Although this provides good protection, the fact that it is 10 mm thick on each iliac crest, it could potentially decrease athletes’ performance with extra width on an already wide iliac crest. Incorporating the idea that narrow iliac crest in felids gives them swift range of motion, the girdle pads can be modified to have a narrower width but also provide the same, if not more, degree of protection. The materials in these protective pads could be replaced with tough carbon fiber coating filled with silicone gel to give durability and compression for better impact absorbance. Polyesters treated with silicone emulsions have a much lesser specific volume (11 mL/g vs 90 mL/g in untreated polyester), higher compressibility (85% vs 49%) and a 9% greater recovery from impact (Naganawa, Ona and Takimoto 2002). The efficacy of carbon-fiber reinforced polyethylene for contact stress tolerance in total joint replacement has been previously described (Bartell, Bicknell and Wright 1987). Besides, the carbon fiber coating which would potentially house the silicone treated polyester is merely 5 to 10 micrometers thick as opposed to the current Under Armour ® model that is 10 mm thick. With its greater strength to weight ratio compared to polyester, the padding would be more durable, even with strong collision force. Therefore, with greater strength of carbon fiber and greater compressibility and recovery of silicone treated polyester, the current polyester model could be replaced. The proposed model would be significantly thinner, providing greater degree of protection without compromising the thinness of iliac crest.

While living organisms have evolved over generations, our understanding of adaptive morphology and behavior has accelerated in an unparalleled fashion. The adaptations in these species is nature’s way of telling us that studying the anatomy of these species can potentially make our everyday lives better. From bionic eye technology, aerospace landing, ballerina pointe shoes to protective sports gear, the snow leopard marks its influence in a diverse set of disciplines outside of biology. Despite being threatened to extinct by the next century, it is the snow leopards’ way of reminding us that it is the king of snowy mountain ranges.   

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