One surprise was finding genes responsible for sensitive odor receptors. As a primarily aquatic animal, the platypus was already known to rely on electrosensory receptors in its bill to detect faint electric fields emitted by underwater prey. So why the considerable ability to sense odors? The scientists speculate that it may involve sexual communication or the use of water-soluble odorants in navigating and hunting underwater.

Fish, on the other fins, usually have a closed circuit to their nostrils. They either have a dead-end pit or a loop that is not connected to their mouth or throat (moray eels). They may have flaps or other convolutions that help channel water past their sensory cells as they move, but they don’t breathe in and out through their nostrils like mammals do. They have gills for that porpoisepurpose.

But you got me think about the platypus and polar bears. I wonder if they are capable of using olfaction underwater. I recall that platypus are supposed to have an electro-conductivity sense along their bills, similar to sharks. And being mammals, they probably do stink.