Human Vs. Animal Smell
There is no doubt that many animals have a sense of smell far superior than humans. This is why, even today, humans use dogs to find lost persons, hidden drugs, and explosives, although research on "artificial noses" that can detect scent even more reliably than dogs continues. Humans are called microsmatic, rather than macrosmatic, because of their humble abilities of olfaction.
Still, the human nose is capable of detecting over 10,000 different odors, some in the range of parts per trillion of air; and many researchers are beginning to wonder whether smell does not play a greater role in human behavior and biology than has been thought. For instance, research has shown that human mothers can smell the difference between a vest worn by their baby and one worn by another baby only days after the child's birth.
Yet some olfactory abilities of animals are probably beyond humans. Most vertebrates have many more olfactory nerve cells in a proportionately larger olfactory epithelium than humans, which probably gives them much more sensitivity to odors. The olfactory bulb in these animals takes up a much larger proportion of the brain than humans, giving them more ability to process and analyze olfactory information.
In addition, most land vertebrates have a specialized scent organ in the roof of their mouth called the vomeronasal organ (also known as the Jacobson's organ or the accessory olfactory organ). This organ, believed to be vestigial in humans, is a pit lined by a layer of cells with a similar structure to the olfactory epithelium, which feeds into its own processing part of the brain, called the accessory olfactory bulb (an area of the brain absent in humans).
The vomeronasal sense appears to be sensitive to odor molecules with a less volatile, possibly more complex molecular structure than the odorants to which humans are sensitive. This sense is important in reproduction, allowing many animals to sense sexual attractant odors, or pheromones, thus governing mating behavior. It is also used by reptilian and mammalian predators in tracking prey.