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Terrestrial mammals exhibit extraordinary sensory diversity adapted to their niches. Carnivores (dogs, cats) have extremely developed olfactory systems: the dog has ~300 million olfactory receptors (vs. 6 million in humans) and ~1200 types of ORs, which allows it to detect concentrations of 10¹ M (one billion times more sensitive than the human for some molecules).

The vibrissae (whiskers) of rodents and carnivores are high-precision tactile systems. As Euler-Bernoulli beams, their flexibility = FL³/(3EI) depends strongly on L and d: long, thin whiskers are very sensitive to small forces. Vibrissa follicles have the greatest innervation of any tactile structure: ~100200 axons per vibrissa. The rat vibrissa cortex (barrel cortex) has a 1:1 somatotopic representation with each vibrissa.

Carnivore night vision uses the tapetum lucidum (reflective layer behind the retina) to give photons a second chance to be absorbed, effectively doubling sensitivity in low-light conditions. The reflection coefficient r_tapetum 0.60.9 increases the sensitivity by 1.61.9×. The cost is loss of spatial resolution (two photons from the same object can arrive from different angles).

Rodents communicate extensively through ultrasonic vocalizations (USVs, 2280 kHz) inaudible to humans, used in courtship, play, and stressful situations. Young produce calling USVs to the mother when separated. The rodent auditory system is especially adapted to these frequencies: the basilar membrane and hair cells are optimized for 1080 kHz.

The vibrissae of seals and walruses (aquatic mammals with highly developed vibrissae) deserve special mention: their wavy vibrissae act as filters that suppress the turbulence inherent to movement (self-motion) but amplify disturbances in the hydrodynamic wake of prey, allowing them to follow fish wakes at distances of up to 35 m with a delay of 30 seconds.

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