I wrote a science fiction esque description of my favourite Pokemon, Fennekin, trying to explain their appearance and the Pokedex entries and other lore surrounding them in a sciencey way. I might write these for other Pokemon if there is enough interest. Please let me know what you think!

The Physiology of Pokémon: Fennekin

Fennekin, the Fox Pokémon, is a fire-type Pokémon primarily native to the Kalos region. In fact, it is the official fire-type starter of the Kalos Pokémon League.

External Anatomy

Fennekin are small, quadrupedal Canid Pokémon, with a nominal adult height of 40 centimeters and an nominal adult weight of 9.4 kilograms. The greatest defining characteristic of Fennekin is its large head in proportion to its body, and its even larger ears in proportion to its head. They have very soft and fine tri-colored fur, with yellow covering most of its body, accented by an orange tip on its short, fluffy tail and in long hairs jutting from its ears, and with a white band on the bottom of its head and its muzzle. The orange accents are thought to be a warning signal to potential adversaries, informing that they are indeed dealing with a Fennekin and to reconsider initiating a confrontation, and potentially also as visual cues for members of a skulk to locate each other.

Fennekin also have long, thick whiskers on its cheeks that helps with tactile feedback when burrowing or venturing into confined areas, as well as longer hair on its back haunches, which provides cushioning when sitting down on rocky ground. Its eyes are white with elliptical orange iris and pupils, oriented vertically, bordered on top by a black stripe on the top eyelid for absorbing excess light in order to reduce glare, and appearing to almost blend into the white fur at the bottom. Below the eyes is a short snout that ends in a black, pointed nose.

Its body is quite small for its head, and is attached to thin legs that terminate in equally thin paws. Retractable claws and a covering of fur make Fennekin’s toes nearly invisible when seen from afar.

Diet and Feeding Adaptations

Fennekin are omnivores, though the majority of their natural diet consist of animal tissue, typically small rodent, bird and bug Pokémon. Due to their small body and their need as a fire-type to convert food to liquid fuel, however, they have evolved a unique adaptation for fire-type Pokémon, the ability to convert plant matter directly into fuel. Fennekins have an affinity for eating twigs, and similar forms of wood, which is broken down in their stomachs primarily by the enzyme pyrocellulase and pyroligninase, which as the names imply, converts the structural fibers of plants to liquid fuels, which is absorbed and transferred to the flame sac to be combusted. A Fennekin’s teeth, though similar in structure to other primarily carnivorous Pokémon, have much stronger enamel to combat the wear that chewing twigs imposes. Eating wood products to convert to fuel allows the Pokémon to reserve less abundant food material strictly for nutrition, instead of wasting them to produce fuel.

A common and potentially harmful myth is that because Fennekin will naturally and frequently seek out twigs to eat, that they can subsist on a vegan diet or even one comprised entirely of wood products. This is not true, as Fennekin do not even use wood for their actual nutritional requirements, only to produce fire. They are still physiologically omnivores that prioritize eating animal matter. Trainers feeding their Fennekin such insufficient diets have caused severe malnutrition, sometimes leading to permanent organ damage and even death. However, feeding a Fennekin wood products before battle is a good way to power up its fire-type attacks, and feeding such materials after battle can help them to recharge their fuel reserves.

Type Specific Adaptations

Fennekin are considered obligate fire-type Pokémon, meaning that its type-specific abilities are essential for its survival. In short, a Fennekin without the ability to produce fire will die very quickly, and a Fennekin that loses its fire ability for even a few hours is likely to sustain organ damage. This is due to the fact that many metabolic processes within a Fennekin have evolved to not only tolerate the very high body temperatures, they require the thermal energy it provides. Certain hormones and neurotransmitters are also not activated until they have passed through regions of particularly high temperatures, in order to regulate their action in the body. Without maintaining a minimum internal temperature of 100 degrees Celsius, chemical functions in a Fennekin’s body will quickly grind to a halt.

Fennekin have an internal flame sack, the same as similar Canid fire-type Pokémon such as Vulpix and Flareon. This sac is located in the upper chest cavity, beside the heart and is connected by a tubule to the back of the mouth, allowing the Pokémon to breathe out flames at will. Inside the flame sac, a small flame is always burning, referred to as the metabolic flame, similar to the flame on Charmander’s tail. The aorta coming off the heart wraps around the flame sac, acting as a heat exchanger and picking up thermal energy and spreading it throughout the body. Trainers are advised to be cautious when tending to a wounded Fennekin, as their blood is boiling hot and will cause burns if it contacts your skin. When discharging fire, the flame sac contracts, forcing the fuel up the tubule toward the mouth. The upper section of the tubule secretes the enzyme pyroinitiatase that activates the self-oxidizing fuel, causing it to rapidly ignite, much faster than it would on its own when maintaining the metabolic flame. The expansion of the fuel as it combusts forces it at high pressure out of the Pokemon’s mouth.

To keep the high temperatures contained in the body, a highly specialized layer of fat just beneath the skin, along with the skin itself, acts as a thermal barrier, allowing them to interact with other Pokémon and humans without causing burns. The insulation also greatly increases the efficiency of a Fennekin’s metabolism. While regions inside a Fennekin’s body can be as high as thousands of degrees Celsius, its skin rarely exceeds the high forties. Still, Fennekin are exceptionally warm to the touch, making them a great companion during the cold Kalos winters.

Fennekin, just like most Pokémon, are still mostly comprised of water. However, with their internal temperatures exceeding the boiling point of pure water, they have evolved to produce a variety of chemicals that when in solution, significantly raises the boiling point of water. If these chemicals were to suddenly disappear from a Fennekin’s body, all the water inside it would turn into steam, causing the unfortunate Pokémon to explode. However, though water inside a Fennekin is essential for life, Fennekin by nature have a distaste for external contact with water sources, with the exception when they need to drink it. This is because water is a very effective sink of thermal energy, not helped by the fact that contact with water causes its skin and its fur to lose their effectiveness as insulators. A submerged Fennekin will quickly lose heat to its surroundings, heat that it needs to survive. Understandably, they have developed a natural stress response to this, and as a result will become extremely agitated when in contact with water. Many a trainer have experienced this when attempting to give their new Fennekin a bath.

Fennekin also has the unique fire-type ability of being able to shoot superheated air out of its large ears. When a Fennekin discharges its flame sac and simultaneously exhales while its mouth is closed, the flame heats the air, which is forced through channels in the skull to the outer ear canals, where it is forcefully ejected. The heat of this action often causes the fur in the ears to become red hot, adding a visual cue. This adaptation is used to both frighten adversaries, and to directly attack them. Fennekin can turn their ears in nearly all directions, allowing them to aim the streams of hot air. Additionally, a Fennekin may either directly discharge fire from its mouth or discharge hot air from the ears if pressures in the flame sac rise to unsafe levels.

Sensory Adaptations

Like many Canid Pokémon, Fennekin have a strong sense of smell, though not as strong as certain Pokémon such as Growlithe. However, a Fennekin’s true sensory superpower is its sense of hearing. Having the largest ears in relation to its body, Fennekin are among the most accomplished listeners of any Pokémon, on par with or even exceeding the Audino in that regard. The large tufts of fur, despite being thought of as obstructing its hearing, actually exists to reduce noise created by wind blowing past the ear canals, which is a common problem in the mountains of Kalos. The hair also protects the ear canals by deflecting water, dust and debris. Recent research have also discovered sensory neurons attached to the base of the hair, suggesting that the it may directly contribute to hearing by detecting ultra low frequencies, known as infrasound. A significant portion of a Fennekin’s brain is dedicated to processing of sound information, much more than all other senses combined.

It is thought that Fennekin hunt by directly listening for the heartbeats of their prey. They have shown evidence of being able to identify individuals from kilometers away simply based on the specific sounds of their heartbeats and breathing. If you own a Fennekin, it likely knows you’re its trainer simply by recognising the sound of your most basic bodily functions.

[I hit the maximum character limit apparently, the last part will be in the comments.]