The parashrew, Pennatacaudus volitarius is a red-toothed shrew from the western mountains of North America that is perhaps the strangest mammal found in any mountainous region.
The adults are unremarkable small, typical-looking shrews, but the juveniles possess one of the strangest devices found in the animal kingdom. At the end of their tails, they have a fantastic parachute structure formed of interwoven hair, which they normally use only once before discarding. When the time comes to leave the parental nest, they launch themselves into the air, relying on the thermal currents that rise from these bare rocky slopes in summer to carry them to a fresh habitat, in some cases several kilometres away. As a means of dispersal this is a bit hit-and-miss, but the inevitable high death rate that this behaviour produces among young parashrews is more than compensated for by the large numbers of offspring produced by each adult breeding pair.
The evolution of the parashrew's parachute tail is primarily due to the creature's ancestry. It is thought that these early creatures used their tails as balancing organs when leaping to catch insects in midair. The parachute consists of soft, curled hairs hooked together to form a mat and held in shape by a series of bristles growing from the tip of the tail.