S5 Terrestrial mammals

Topic

This mammal exhibits great sensory diversity, adapted to each species' ecological niche. A dog possesses an extremely well-developed olfactory system, featuring numerous functional olfactory receptors and receptor types—far exceeding the numbers found in the human equivalent modeled elsewhere in this set. Utilizing the same receptor-ligand binding kinetics described in another model within this set, the dog can detect extraordinarily low concentrations of odorant molecules. Its greater diversity of functional olfactory receptors also enhances its ability to discriminate between different odor mixtures.

In contrast, the vibrissa (whisker) of a rodent or carnivore serves as a highly precise tactile system. Its flexion in response to force can be modeled analogously to an Euler-Bernoulli elastic beam; consequently, its sensitivity depends heavily on its length and thickness: a long, thin vibrissa deforms more under a given force than a short, thick one. Its follicle is richly innervated with sensory nerves, and in rats, each vibrissa has a specific representation within the somatosensory cortex. A longer, thinner vibrissa offers increased sensitivity to slight contact forces.

Many carnivores, however, rely on the *tapetum lucidum*—a reflective layer located behind the retina—for night vision. This layer reflects light that initially passed through the retina without being absorbed back toward the photoreceptors, providing a second chance for detection and thereby increasing sensitivity in low-light conditions. This advantage may come at the cost of reduced spatial precision due to light scattering and reflection. A *tapetum lucidum* that reflects a higher proportion of photons enhances night vision, though potentially at the expense of spatial resolution. Rodents also employ ultrasonic vocalizations—inaudible to humans—during social interactions such as courtship and play, as well as in certain stressful situations. A pup separated from its mother may produce ultrasonic calls, while its auditory system possesses adaptations enabling it to respond to frequencies far above the human audible range—a feature also found in another model in this set. If the conditions triggering these calls persist, the pup may continue to emit them repeatedly.

An additional specialization is found in the vibrissae of seals and other pinnipeds. Their geometry minimizes the disturbance caused by the animal's own movement while maintaining sensitivity to external hydrodynamic changes. A seal can thus detect and track the wake left by prey that previously swam through the area, much like a fish detects flow fields using its lateral line—a mechanism also featured in another model in this set. This capability requires distinguishing the signal produced by the prey from the noise associated with the animal's own movement. Because hydrodynamic wakes persist longer in water, the seal can detect and follow them at a greater distance from the point of origin.

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