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Pet owners are familiar with the feel of a wet noseusually at 6 in the morning when Fido decides it’s time for breakfast. In fact, most mammals have this most surface around their nostrils, known as the rhinarium. Primates are the only group in which some species do not have this feature.The rhinarium surrounds the nostrils and features a thin groove in the center, known as the philtrum. While it’s indubitably part of the olfactory system, researchers debate whether it is part of the Main Olfactory System or the Accessory Olfactory System. The main difference between the systems is the type of smell they detect bestthe Main system detects “media-borne” smells, while the Accessory system has proven more adept at detecting the smells of fluids. Whatever the case, the rhinarium’s wrinkled surface must help to improve its surface area, and thus improve reception.Different mammals have different rhinariums based on their environment and activities. Swimming mammals developed lobes which can close over the nostrils during diving, while mammals that root have a rhinarium with a hard pad, with the nostrils off to the side. The walrus’s rhinarium is protected by bristles, while the elephant has adapted it into its main tactile organ.The loss of the rhinarium in humans and some other primates (known as the haplorrhines, or “dry-nosed primates”) led to a decrease in our sense of smell. Researchers suspect this is due to a loss of reliance on olfaction for survivalin contrast, many animals with rhinariums benefit because it helps to alert them to wind direction. In closing, the next time Fido rubs his nose on you to tell you he loves you, be confident that he’s using his natural abilities for all they’re worth.