Sure, turtles and tortoises are weird. They're egg-laying, scaly reptiles with oval-shaped hard shells. They lumber around incredibly slowly and have wrinkly, bald heads that make them look like wise old men.
And let's not forget their signature ability to retract their heads inside their shells when they're frightened.
But believe it or not, these animals can get even weirder.
Click ahead to find out what sets these members of the biological order Chelonia apart from everything else under the sun.
10. That Shell isn't What it Seems
Chelonians' shells look a little like human body armor, so one might conclude that they're reptilian versions of the powered exoskeleton that makes Iron Man such a fearsome superhero. But the shell, which is made up of about 50 different bones, actually is an evolutionary modification of the rib cage and part of the vertebral column. And contrary to what you may have seen in animated cartoons, a chelonian can't take off its shell and crawl out of it -- just as you couldn't dismantle your own spine and ribs, according to the University of Michigan Museum of Zoology.
The shell itself actually has two parts: an upper section, the carapace, and a lower portion called the pastron, which are joined by a bony bridge. Some turtles have a moveable joint, usually in the plastron, that acts as a hinge and enables the creature to pull the two shell sections together tightly while it retracts its body inside. Shells have nerves embedded in them and a blood supply as well, so if a chelonian's shell is injured, it may bleed and feel pain.
9. Tortoises Orbited the Moon Before Astronauts Did
In September 1968, the Soviet Union launched the space probe Zond 5 on a mission to orbit the moon and test conditions as a prelude to a possible lunar mission by cosmonauts. In addition to a life-size human mannequin equipped with radiation detectors, the spacecraft carried a number of living passengers, including a pair of Russian tortoises that newspaper reports initially described as "turtles." After a week in space, Zond 5 returned to Earth and, despite a failure of crucial altitude detectors, successfully splashed down in the Indian Ocean.
Along with the other creatures, the tortoises were rescued and brought back to the Soviet Union for study. The Soviets revealed that the tortoises had lost about 10 percent of their body weight, and showed an "excessive content" of glycogen and iron in their liver tissue and some changes in their spleens. Otherwise, though, the tortoises remained active and showed no loss of appetite, according to NASA.
8. Alligator Snapping Turtles Lure Prey With Their Tongues
One of the most fearsome Chelonians around is the alligator snapping turtle, Macroclemys temminckii, which is the biggest freshwater turtle in North America. It can grow to 2.5 feet long, can weigh as much as 200 pounds, and has powerful jaws, a sharply-hooked beak, nasty bearlike claws and a muscular tail. The alligator snapping turtle does eat some aquatic plants, but it's mostly a carnivore that dines on a variety of smaller creatures -- fish, frogs, snakes, worms, clams, crayfish and even other turtles.
The alligator snapping turtle catches prey by way of a fiendishly clever evolutionary adaptation: an appendage to its tongue that, when wriggled, looks an awful lot like a worm, according to the Saint Louis Zoo. A fish who gets fooled by the turtle's tongue will swim right into range of the hungry predator's jaws.
7. They Make Sounds, Even Though They Lack Vocal Cords
Chelonians can make sounds by swallowing or by forcing air out of their lungs, and some species emit unique noises. The red-footed tortoise (Chelonoidis carbonaria), a South American species, makes a series of clucks that sound like a chicken. Male Travancore tortoises (Indotestudo forstenii) in Southeast Asia emit a high-pitched whine that sounds like an electric motor when they're seeking mates. The giant musk turtle (Staurotypus salvinii), which is found in Central America, is known for yelping like a dog when it's startled or being attacked.
But the weirdest sound is made by nesting female leatherback sea turtles (Dermochelys coriacea), who make a distinctly unladylike noise that resembles a human belching, according to the book Turtles: An Extraordinary Natural History 245 Years in the Making.
6. Males Select Potential Mates By Sniffing Tails
OK -- so humans shouldn't really talk, since we have some pretty silly mating behavior of our own, including selecting potential partners on the basis of their dancing ability or zodiac sign. In comparison, perhaps male chelonians' method of sniffing under other female chelonians' tails is relatively sensible, not to mention functional.
Since both males and females' sexual organs are hidden inside their cloaca, a cavity used for both reproduction and eliminating waste, humans have trouble telling by sight which shelled creature is female and which is male. Turtles and tortoises, however, possess an extremely keen sense of smell. According to Turtles: An Extraordinary Natural History 245 Years in the Making, males apparently can detect the scent of pheromones, a type of identifying chemical, that is secreted inside a female's cloaca. Chelonians rely on scent so heavily that a male red-footed tortoise once was observed trying to mount a head of lettuce that a female had just climbed over, according to the book Behavior of Exotic Pets.
5. They Don't Have Ears, But Can Perceive Low-Pitched Sounds
You may have heard that turtles and tortoises, which lack an ear opening, are deaf, but that's not completely accurate. It's true that chelonians can't hear anywhere near as well as humans and many other species can. But they can detect certain types of sounds. Scientists who've used light microscopes to study the ear structure of marine turtles, for example, have found that their middle ears have a very thick eardrum-like membrane, which limits the frequency range they can perceive. But that adaptation is extremely efficient for bone conduction hearing at low frequencies, according to Behavior of Exotic Pets.
According to reptile expert Melissa Kaplan, Chelonians generally can perceive sounds in the 50 to 1,500 Hz range, compared to the typical human hearing range of 20 to 20,000 Hz. Our hard-shelled friends also can't differentiate loudness as well as we can. The spotted turtle (Clemmys guttata), for example, has a peak sensitivity of just 4 dB, compared to 120 dB in humans. The upshot is that while turtles and tortoises may not be able to appreciate, say, the nuances of Mahler's "Symphony No. 2," their sense of hearing is good enough to detect the presence of predators.
4. Turtles Are Nearly As Old As The Dinosaurs
Chelonians and dinosaurs emerged and developed at pretty much the same time, in natural history terms. The oldest known fossil turtle, Odontochylys semitstacea, dates back 220 million years, which means it showed up 23 million years after the earliest known dinosaur relative, Asilisaurus kongwe. That long-extinct ancient turtle had a partial shell covering its belly, but it didn't extend to completely protect its back, like the ones that modern chelonians have, according to National Geographic.
Amazingly, some turtles that existed in the age of the dinosaurs are still around. Pelomedusidae, a family of freshwater turtles native to eastern and southern Africa, first appeared about 120 million years ago. The first tortoises emerged on land at the start of the Tertiary Period 65 million years ago, shortly after the dinosaurs died out in a mass extinction. In the ocean, the oldest surviving species of sea turtles, the Cheloniidae, date back 55 million years, according to the book Turtles of the World.
3. Turtles Breathe Without A Diaphragm
Most air-breathing vertebrates draw air in and out of their lungs using a diaphragm, which is a muscle that contracts and relaxes with each breath to expand the ribs. It's pretty easy to tell when one's breathing because its body moves. But turtles don't have a diaphragm, which is all well and good, since the rigidity of their shells would prevent their ribs, which are connected to them, from expanding. Instead, turtles must move their limbs or neck, and utilize other muscles connected to the pleural cavity (the area around the lungs), to help them breathe.
Some turtles also have special muscles situated between their limbs and lungs to aid in breathing, or they have an additional breathing-related trick that allows them to remain underwater for longer periods. According to the book Turtles: An Extraordinary Natural History 245 Years in the Making, some turtles use buccopharyngeal breathing, in which they take water into their mouths and then pass it out of their nostrils. Along the way, the oxygenated water passes along the capillary-rich tissue inside their necks, allowing additional oxygen to enter directly into the bloodstream.
2. They Have Favorite Colors
Like us, our shell-wearing reptilians are visually oriented creatures. They rely on sight to identify other members of the same species, food, and potential danger, such as predators. Sea turtles, for example, are so dependent on sight that when researchers blindfolded some of them, the animals were unable to find their way back into the water.
Research also shows that turtles not only can perceive colors, but that certain colors -- red, orange and yellow -- seem to be the most appetizing to them. When they see an object in one of those shades, they display "investigative behavior," which suggests that they're checking it out to see if they want to eat it, according to Turtles: An Extraordinary Natural History 245 Years in the Making.
1. There's A Turtle That Seems Part Skunk
The African helmeted turtle, Pelomedusa subrufa, is the most widespread turtle species in Africa. It's found just about everywhere south of the Sahara desert. It's a hunter-scavenger that hunts in packs and seems happy to eat most anything, from parasites lodged in the skin of rhinoceroses to young birds and small mammals, according to Turtles of the World. It attacks ducklings by dragging them underwater, and steals bait from anglers' hooks, habits which make it disliked by many Africans.
But the helmeted turtle's reputation is not just odious, but odorous as well. It smells really, really awful. That aroma comes from four glands, one under each leg, which release a foul-smelling liquid seems to repulse horses as well as humans, according to the International Wildlife Encyclopedia. Despite that unpleasant odor, villagers sometimes dig up the turtles from their mud nests during wet season for food. However, the smelly shelled creatures don't have enough meat on them to make a very satisfying meal, according to Turtles of the World.