EARTH'S ORGANISMS
animals faces senses ecology evolution adaptation

What Happened to Your Nose?

Fancy schnozzes have surprising functions across the mammal family tree.

Elephants, kangaroos, mice, monkeys, beavers, whales, tigers, goats—all of these creatures are mammals. While their sizes and shapes are diverse, their faces are usually pretty standard: two eyes, two nostrils, a mouth, and two ears. The faces can be different colors and have varying amounts of hair, but the general pattern is conserved across mammals. Every now and then, though, evolution produces a real weirdo—in the best sense of the term. It turns out a bizarre facial appendage can have many uses when it comes to sensing and moving through the world. Here are some animals that don’t care how strange you think they look because they are too busy being well adapted to their environments!

Leaf-nosed bats:

image alt text Fig. 1 The Honduran white bat (Ectophylla alba) belongs to a family of tropical bat species with super diverse nose leaf structures. Leaf-nosed bats eat everything from insects to fruit to nectar to fish and other animals, using their nose leaves to help with echolocation. Image source: Leith Miller

Bats use echolocation to “see” by bouncing very high-pitched calls off of their surroundings and listening to the returning sound waves, which they use to construct a detailed and dynamic picture of their environment. Although many species of bats also use vision and smell to navigate and forage for food, echolocation provides such an advantage for these nocturnal animals that they have many specialized adaptations to fine-tune the process. One of these is the striking “nose leaf” seen above in this picture of a Golden Bat from the South American rain forest. This bat, and many others in this family, emit echolocation calls through their nose. Scientists think that moving the flexible nose leaf structure helps these bats to direct the sounds emitted and echolocate more efficiently [1]. The nose leaf is pretty strange, kind of adorable, and ultimately a cool functional adaptation that has been modified by dozens of species of bats to suit different prey capture styles in different environments.

Star-nosed moles:

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Fig. 2 The Star-nosed mole (Condylura cristata) uses its fleshy face appendage to gather sensory information about its environment. Image source: gordonramsaysubmissions via Flickr Creative Commons.

The star-nosed mole looks like a furry alien with a horror-movie hand where its nose should be. It’s native to eastern North America and is related to other common mole species with less fancy faces. A strong swimmer, it’s just as happy looking for food in the water as in the soil. The star-nosed mole can independently move the 22 fleshy appendages of its “star” and uses them kind of like a hand-eye hybrid to create a picture of its surroundings through touch. Researchers have found that moles touch the star appendages to their surroundings on average 13 times per second while foraging underground, helping them rapidly identify and consume insect prey [2]. This specialized sensory organ won’t win the star-nosed moles any beauty contests, but it is an interesting adaptation to life underground and underwater, where tactile sense is more useful than eyesight.

Tapirs:

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Fig. 3 The Malayan tapir (Tapirus indicus) is part of the family of hooved mammals that includes horses and rhinos. It has three toes on each foot, a mobile proboscis on its face, and is dressed as a panda for Halloween. (Just kidding—baby tapirs start out with spots and stripes for camouflage, but adult Malayan tapirs have this distinctive black and white coloring). Image source: Wikimedia Commons.

As a professional mammalogist, my opinion is that tapirs are overall kind of silly looking. However, this hooved mammal (related to horses and rhinos and found wandering peacefully through the rainforests in Asia and South America) has an extra-funny nose. In fact, the tapir looks like an elephant that didn’t try hard enough—but it’s removed from the evolutionary lineage that includes elephants by tens of millions of years. The tapir’s proboscis, or dangly nose, is similar to an elephant’s trunk in that it can move independently, but it’s nowhere near as flexible or dexterous as an elephant. Instead, it functions as a sort of mobile lip with extra scent-detecting capabilities, helping the tapir pinpoint the direction of different smells by moving its nostrils around [3]. In addition to being a specialized sensory structure, the tapir’s probsocis can also function as a snorkel! Tapirs have been known to cruise around with only their outstretched snouts visible above the water.

There are many other animals out there with weird faces (or strange limbs, quirky feet, bizarre tails, etc.). But if you dig a little deeper, you can often find that what looks like a bad decision made by an intoxicated sci-fi movie prop designer is in fact a specialized organ shaped by hundreds of thousands of years of natural selection to perform a specific function really well. We don’t always know what that function is, but the fun of evolutionary biology is figuring it out!

References:

  1. Pedersen, Scott C. and Rholf Muller, “Nasal-Emission and Nose Leaves” in Bat Evolution, Ecology, and Conservation, ed. Rick A. Adams and Scott C. Pedersen, 71-91. New York: Springer Press, 2013.

  2. Catania, Kenneth C. and Fiona E. Remple. “Tactile Foveation in the Star-Nosed Mole.Brain, Behavior, and Evolution 63 (2003): 1-12.

  3. Milweski, Antoni V. and Ellen S. Dierenfeld. “Structural and functional comparison of the proboscis between tapirs and other extant and extinct vertebrates.” Integrative Zoology 8 (2013): 84-94.

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