Science, Tech, Math › Animals & Nature The 10 Weirdest Animal Facts Share Flipboard Email Print Dugong. Getty Images Animals & Nature Dinosaurs Prehistoric Mammals Basics Paleontologists Carnivores Dinosaurs & Birds Herbivores Marine Reptiles Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Marine Life Forestry Evolution View More By Bob Strauss Science Writer B.S., Cornell University Bob Strauss is a science writer and the author of several books, including "The Big Book of What, How and Why" and "A Field Guide to the Dinosaurs of North America." our editorial process Bob Strauss Updated November 03, 2017 Some animal facts are weirder than others. Yes, we all know that cheetahs can run faster than motorcycles, and that bats navigate using sound waves, but those tidbits of information aren't nearly as entertaining as immortal jellyfish, butt-breathing turtles, and three-hearted octopuses. Below you'll discover 10 truly weird (and true) facts about 10 truly weird (and real) animals. 01 of 10 Female Spotted Hyenas Have a Penis Getty Images Okay, it may be a bit of an overstatement to say that the female spotted hyena has a penis: more accurately, the clitoris of the female closely resembles the penis of the male, to the extent that only a very brave naturalist (presumably wearing gloves and protective headgear) could hope to tell the difference. (For the record, the female's sex organ is slightly thicker, with a more rounded head than that sported by males.) Only slightly less weirdly, spotted hyena females are dominant during courtship and mating, and prefer to hook up with younger males; clearly they're the "cougars" of the mammal family. 02 of 10 Killer Whales Experience Menopause Getty Images The menopause of human females is one of the mysteries of evolution: wouldn't it be better for our species if women could give birth throughout their lives, rather than becoming infertile around the age of 50? This enigma isn't diminished by the fact that only two other mammals are known to experience menopause: the short-finned pilot whale and the orca, or killer whale. Female killer whales stop bearing children when they reach their 30's or 40's; one possible explanation is that elderly females, undistracted by the demands of pregnancy and birth, are better able to guide their pods. This is the same "grandmother effect" that has been proposed for elderly human females, who provide inexhaustible supplies of wisdom (and babysitting). 03 of 10 Some Turtles Breathe Through Their Butts Wikimedia Commons A handful of turtle species—including the North American eastern painted turtle and the Australian white-throated snapping turtle—have specialized sacs near their cloacas (the organs used for defecating, urinating, and copulating) that collect air and filter out oxygen. However, these turtles are also equipped with perfectly good lungs, which begs the question: why breathe through your butt when your mouth will do? The answer likely has something to do with the tradeoffs between hard, protective shells and the mechanics of respiration; apparently, for these turtles, butt-breathing is less metabolically demanding than mouth-breathing. 04 of 10 One Species of Jellyfish Is Immortal Getty Images Before we talk about immortal jellyfish, it's necessary to define our terms. Turritopsis dohrnii will definitely kick the marine bucket if you step on it, pan-fry it, or torch it with a flamethrower. What it won't do, however, is die of old age; the adults of this jellyfish species can reverse their life cycles all the way back to the polyp stage, and (theoretically) repeat this process an indefinite number of times. We say "theoretically" because, in practice, it's virtually impossible for a single T. dohrnii to survive for more than a few years; that would require a given individual (either polyp or adult) to avoid getting eaten by other marine organisms. 05 of 10 Koala Bears Have Human Fingerprints Getty Images They may seem cute and cuddly, but koala bears are extremely devious: not only are they marsupials (pouched mammals) rather than true bears, but they have somehow managed to evolve fingerprints virtually indistinguishable from those of human beings, even under an electron microscope. Since human beings and koala bears occupy widely separated branches on the tree of life, the only explanation for this coincidence is convergent evolution: just as early Homo sapiens needed a way to firmly grasp primitive tools, koala bears needed a way to grasp the slippery bark of eucalyptus trees. 06 of 10 It's Almost Impossible to Kill a Tardigrade Getty Images Tardigrades—also known as water bears—are microscopic, eight-legged, vaguely repulsive-looking creatures that can be found pretty much everywhere on earth. But the weirdest thing about tardigrades, apart from their nightmarish appearance, is that they're pretty much indestructible: these invertebrate animals can survive prolonged exposure to the vacuum of deep space, endure bursts of ionizing radiation that would fry an elephant, go without food or water for up to 30 years, and prosper in terrestrial environments (Arctic tundra, deep-sea vents) that would kill most other animals, including human beings. 07 of 10 Male Seahorses Give Birth to Young Getty Images You might think the spotted hyena (previous slide) is the last word for gender equality in the animal kingdom, but you don't know about seahorses yet. These marine invertebrates pair up for elaborate, intricately choreographed mating rituals, after which the female deposits her eggs into a pouch on the male's tail. The male carries the fertilized eggs for two to eight weeks (depending on species), its tail slowly swelling up, and then releases up to a thousand tiny seahorse babies to their fate (which mostly involves being eaten by other marine creatures; sadly, only one-half of one percent of seahorse hatchlings manage to survive into adulthood). 08 of 10 Three-Toed Sloths Wear Algae Coats Getty Images Just how slow is the three-toed sloth? Not much faster than you saw in the movie Zootopia; this South American mammal, when it isn't entirely motionless, can hit top speeds of a blazing 0.15 miles per hour. In fact, Bradypus tridactylus is so crepuscular that it can easily be overtaken by unicellular algae, which is why most adults sport shaggy green coats, making them (for all intents and purposes) equal parts plant and animal. There is a good evolutionary explanation for this symbiotic relationship: the green coats of three-toed sloths provide valuable camouflage from jungle predators, notably the much, much faster jaguar. 09 of 10 Octopuses Have Three Hearts and Nine Brains Getty Images There's a reason vaguely octopus-like creatures often feature in science-fiction movies as super-intelligent aliens. The anatomy of octopuses is alarmingly different from that of humans; these invertebrates have three hearts (two of which pump blood through their gills, the other to the rest of their bodies), and nine aggregations of nerve tissue. The primary brain resides, appropriately enough, in the octopus' head, but each of its eight arms also contains its share of neurons, which allow for independent movement and even primitive "thinking." (Let's keep things in perspective, though: even the smartest octopus only has about 500 million neurons, one-twentieth the amount of the average human.) 10 of 10 Dugongs Are Closely Related to Elephants Getty Images You might naively assume that dugongs—the awkward-looking marine mammals that drunken sailors once mistook for mermaids—are most closely related to seals, walruses, and other pinnipeds. The fact is, though, that these ocean dwellers descend from the same "last common ancestor" that spawned modern elephants, a tiny quadruped that lived on dry land about 60 million years ago. (Dugongs belong to the same family, the sirenians, as manatees; these two mammals went their separate ways about 40 million years ago.) The exact same pattern was repeated by (unrelated) whales, who can trace their ancestry to a population of dog-like mammals that lived during the early Eocene epoch.