Pangolin Lungs and Respiratory System Anatomy

The respiratory challenges facing pangolins are unlike those of almost any other mammal. At various points during an ordinary night's activity, a pangolin may be holding its breath inside a termite mound gallery filled with biting insects, resting in a sealed burrow two metres underground with declining oxygen levels, or curled into a defensive ball with its airway partially compressed by the curled posture. Each of these scenarios demands something specific from the respiratory system, and the anatomy pangolins have evolved to meet these demands reflects both the opportunities and the constraints of their unusual ecological niche.

Lung Structure and Lobes

Pangolin lungs follow the general mammalian plan: a pair of organs occupying the thoracic cavity on either side of the heart and mediastinum, enclosed within the ribcage and separated from the abdominal cavity by the muscular diaphragm. The right lung is typically divided into more lobes than the left in most mammals, and this asymmetry is present in pangolins as well, though the precise lobar configuration has been described in detail only for a limited number of specimens. The left lung, positioned alongside the heart, is slightly smaller and less elaborately lobed than the right.

The diaphragm is the primary muscle of inspiration. When it contracts, it flattens and descends, increasing the volume of the thoracic cavity and drawing air into the lungs through the reduction in intrapulmonary pressure. The external intercostal muscles provide supplementary expansion of the rib cage during deeper breaths. This standard mammalian breathing mechanism functions normally in pangolins under resting conditions, but the diaphragm's role becomes more complex during the various non-standard respiratory situations the pangolin regularly encounters.

Tidal volume — the amount of air moved with each normal breath — in pangolins scales broadly with body mass in the manner expected for a mammal of their size, roughly 0.5 to 1.5 kilograms depending on species and individual. There are no published measurements indicating that pangolin tidal volume is exceptional in either direction. The alveolar surface area, which determines the efficiency of gas exchange between air and blood, is similarly consistent with general mammalian scaling. The functional respiratory adaptations in pangolins are not primarily about the lungs themselves being anatomically unusual, but rather about the upstream control mechanisms, nasal anatomy, and behavioural integration that allow the respiratory system to operate effectively in difficult conditions.

Breathing While Foraging in Termite Mounds

Foraging inside a termite mound presents an immediate respiratory problem: the galleries are narrow, the air within them is depleted of oxygen and enriched in carbon dioxide compared with ambient air, and the mound is filled with soldier termites biting at every exposed surface. The pangolin's solution is to seal the respiratory tract entirely and hold its breath for the duration of each foraging bout within the mound.

The muscular nasal valves — strong sphincter-like muscles surrounding the nostrils — contract to seal the nasal passages completely. The ears are similarly sealed by muscular action, preventing termites from entering the ear canal. In this sealed state, the pangolin relies entirely on oxygen already stored in the lungs from the last breath taken outside the mound. The foraging action is rapid: the long sticky tongue is inserted and retracted repeatedly, scooping up termites with each stroke, while the animal remains motionless or shifts its body position minimally to access different gallery openings.

The duration for which a pangolin can sustain this breath-holding varies. Field observations from researchers tracking Temminck's ground pangolins in southern Africa suggest that individual mound-raiding episodes last from under a minute to several minutes, after which the pangolin withdraws, opens its nostrils, breathes for a period, and then re-engages. The chemoreceptors in the carotid bodies and medullary respiratory centres that monitor blood carbon dioxide and oxygen levels presumably trigger the withdrawal when the arterial carbon dioxide concentration rises above a threshold, or when oxygen saturation declines to a level that prompts the drive to breathe. Whether pangolins show any suppression of this chemoreceptor sensitivity — a form of diving reflex adaptation — compared with other terrestrial mammals is not established, but it is a plausible direction for future physiological investigation.

Nasal Anatomy and Olfactory Adaptations

The pangolin nose is anatomically remarkable, though its most remarkable features are olfactory rather than purely respiratory. The external nostrils are situated at the tip of the long, tapering snout, and the nasal passages run the full length of this snout before connecting with the pharynx. This extended nasal passage means that inhaled air travels a considerable distance before reaching the lungs, which allows for substantial warming and humidification of cold dry air — an advantage in the cool nights of southern African savanna environments.

The turbinate bones — thin, scroll-shaped bony projections within the nasal cavity — are elaborately developed in pangolins. The ethmoturbinates, which carry the olfactory epithelium, are particularly large, reflecting the importance of olfaction to a nocturnal animal that locates termite mounds primarily by scent. Pangolins are believed to detect termite colonies and ant nests at distances of tens of metres, following scent plumes across the ground surface with considerable precision. The olfactory epithelium is correspondingly extensive, densely packed with olfactory receptor neurons that transduce chemical signals into the neural impulses processed by the olfactory bulb.

The muscular nasal valves that seal the nostrils during mound foraging are anchored to the cartilaginous framework of the snout tip. In pangolins, this framework is unusually robust, providing a firm base against which the sphincter muscles can generate sufficient force to maintain a complete seal even when the snout is pressing into soft soil or termite mound material. The seal must be maintained against not just airflow but also the physical pressure of biting termite soldiers attempting to access the nostrils — a mechanical as well as physiological barrier.

Respiratory Rate and Metabolic Rate

Pangolins have a lower basal metabolic rate than would be predicted for a eutherian mammal of their body mass by standard allometric scaling. This metabolic depression, documented most thoroughly in the Chinese pangolin (Manis pentadactyla) but consistent with observations from African species, means that resting pangolins consume oxygen and produce carbon dioxide at a slower rate than expected. The consequence for respiratory physiology is that the resting respiratory rate is correspondingly low: pangolins breathe slowly and shallowly at rest, which is consistent with their generally torpid daytime behaviour and their tendency to sleep in burrows or hollow trees during the hours of daylight.

When active at night, foraging across distances that may exceed several kilometres per night in productive habitat, oxygen demand increases substantially. The respiratory rate rises accordingly, and cardiac output increases to deliver more oxygenated blood to the working muscles. However, even during active foraging, pangolins are not high-speed athletes — they move at a deliberate walking pace and the energetic demand of locomotion is moderate compared with a running predator or prey animal. The respiratory system is not required to sustain extreme aerobic demands, and the lungs appear adequate to meet the oxygen needs of even the most energetically demanding nocturnal foraging bout without placing the animal close to its aerobic ceiling.

Nocturnal activity patterns also interact with temperature in ways relevant to respiration. In the Limpopo lowveld or the Kalahari sandveld at night, ambient temperatures can fall considerably, and cold air inhalation requires the nasal passages and turbinates to warm the air before it reaches the delicate alveolar tissue. The extended nasal passage and well-vascularised turbinate network serve this thermoregulatory respiratory function alongside their olfactory roles.

Protective Respiratory Mechanisms

Beyond nostril sealing, pangolins have several additional mechanisms that protect the respiratory tract during foraging. The eyelids are thick and toughened, protecting the eyes from biting insects, and this protection extends to the skin around the nostrils. The hairless facial skin of pangolins is relatively tough, and the muscles around the nasal openings are not merely capable of sealing but also of actively pressing the nostrils closed against physical intrusion by soldier termites or ants.

Mucus production in the nasal passages provides an additional layer of defence. The mucosa lining the nasal cavity secretes mucus that traps dust, soil particles, and small insect fragments that might otherwise be inhaled during foraging. This is especially relevant when the pangolin's snout is physically inserted into a termite mound, where fine particulate material is disturbed. The mucociliary escalator — the system of ciliated cells that moves mucus and trapped material toward the pharynx for swallowing — functions in pangolins as it does in other mammals, clearing the nasal passages of material accumulated during foraging once normal breathing resumes.

Respiratory disease in wild pangolin populations is not frequently documented, in part because sick wild pangolins are rarely encountered and in part because systematic health surveillance of wild populations is limited. The protective mechanisms described above likely reduce the incidence of airway infections that might otherwise follow from repeated exposure to the microbe-rich environment of termite mounds and soil.

Breathing During Defensive Curl

When a pangolin curls into its defensive ball, the head is tucked under and the tail wraps around to complete the enclosure. This posture places the spine in extreme flexion and compresses the abdominal contents upward against the diaphragm. The thoracic cavity volume is reduced by the curled position, which means that tidal volume during defensive curling is mechanically constrained — the diaphragm cannot descend as far as it would in a prone or standing animal because the abdominal viscera are pressing against it from below.

Despite this constraint, pangolins can maintain respiratory function during defensive curling, albeit at a reduced tidal volume. They compensate partly by increasing respiratory rate, maintaining minute ventilation (the total volume of air moved per minute) at a level adequate for their oxygen needs while in this position. The airway itself remains patent throughout the curled posture — the trachea and larynx are protected within the body of the curl rather than compressed, and the head's tucked position, while restricting the space available, does not occlude the airway.

During prolonged defensive curling in response to a persistent predator, the stress response also affects cardiovascular function, with elevated heart rate and peripheral vasoconstriction potentially altering the distribution of blood flow and the efficiency of gas exchange. These interactions between the defensive posture, the cardiovascular stress response, and respiratory function represent an interesting area of pangolin physiology that has received limited formal study but is likely to reveal further adaptations as research methods improve.

Burrowing and Hypoxic Tolerance

Temminck's ground pangolin is a proficient burrower, capable of excavating burrows up to two metres in depth using its powerful forelimbs and heavy claws. These burrows serve as daytime sleeping sites, as refuges during bad weather, and sometimes as sites where females den with young offspring. A sealed or partially sealed burrow, particularly one occupied by a sleeping pangolin that has blocked the entrance with soil or its own body, will experience a gradual depletion of oxygen and accumulation of carbon dioxide as the occupant's metabolism consumes oxygen over the sleeping period.

While a two-metre burrow is not sealed in the manner of a hypoxic laboratory chamber, the restricted airflow in a narrow tunnel with a large animal occupying much of the cross-section can lead to meaningful reductions in oxygen partial pressure over a prolonged rest period, particularly in warm conditions where metabolic rate is higher. Whether pangolins show any physiological tolerance to mild hypoxia — such as a higher haemoglobin oxygen affinity, a greater haematocrit, or a suppressed ventilatory response to low oxygen — compared with non-burrowing mammals has not been definitively established. However, the combination of a lower basal metabolic rate (which extends the time before oxygen depletion becomes critical in a closed space) and what may be a modestly elevated tolerance for elevated carbon dioxide (suggested by their breath-holding behaviour during foraging) provides a plausible basis for adequate function in the semi-hypoxic burrow environment. Further physiological investigation of oxygen transport parameters in pangolin blood would be valuable in resolving this question.