What Is the Difference Between...?

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Dolphins and Porpoises, Turtles and Tortoises, and Other Animal Distinctions

A Galapagos tortoise. Getty Images

In a lineup, could you distinguish between a donkey and a mule? No? How about a possum and an opossum? Still no dice? If you need a refresher course in the subtle (and sometimes not-so-subtle) differences between seemingly identical animals, we'll teach you how to tell an alligator from a crocodile, a frog from a toad, and (generally speaking) any kind of critter from a closely related kind of critter.

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Dolphins and Porpoises

A bottlenose dolphin. NASA

Dolphins and porpoises are both cetaceans, the same family of mammals that also includes whales. Dolphins are more numerous than porpoises (34 identified species, compared to six) and are characterized by their relatively long, narrow beaks studded with cone-shaped teeth, their curved or hooked dorsal (back) fins, and their relatively slender builds; they can also make whistling sounds with their blowholes, and are extremely social animals, swimming in extended pods and interacting easily with humans. Porpoises have smaller mouths filled with spade-shaped teeth, triangular dorsal fins, and bulkier bodies. As far as anyone has been able to tell, porpoises can't produce any blowhole sounds, and they are also much less social than dolphins, rarely swimming in groups of more than four or five and behaving very shyly around people.


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Turtles and Tortoises

A pair of green sea turtles. Getty Images

Distinguishing turtles from tortoises is just as much a matter of linguistics as it is of biology. In the U.S., "turtles" generally means both turtles and tortoises, whereas in the U.K., "turtles" refers specifically to freshwater and saltwater testudines (the animal order that embraces turtles, tortoises and terrapins). (We won't even mention Spanish-speaking countries, where all testudines, including turtles and tortoises, are called "tortugas.") Generally speaking, the word tortoise refers to land-dwelling testudines, while turtle is more commonly reserved for ocean-dwelling or river-dwelling species. In addition, most (but not all) tortoises are vegetarians, while most (but not all) turtles are omnivorous, eating both plants and other animals. Confused yet?

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Mammoths and Mastodons

A woolly mammoth. Getty Images

Before we get to the differences, we can tell you one thing mammoths and mastodons definitely have in common: they have both been extinct for over 10,000 years! What paleontologists refer to as mammoths belonged to the genus Mammuthus, which originated in Africa about five million years ago; mammoths tended to be extremely large (four or five tons), and some species, like the Woolly Mammoth, were draped with luxurious pelts. Mastodons, by contrast, were slightly smaller than mammoths, belonged to the genus Mammut, and had a deeper evolutionary history, their distant ancestors roaming North America 30 million years ago. Mammoths and mastodons also pursued different diets: the former grazed on grass like modern elephants, while the latter feasted on the twigs, leaves, and branches of trees.

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Hares and Rabbits

A European rabbit. Getty Images

The terms may be used interchangeably in old Bugs Bunny cartoons, but in fact, rabbits and hares belong to different branches of the lagomorph family tree. Hares are comprised of about 30 species of the genus Lepidus; they tend to be slightly larger than rabbits, live on prairies and deserts rather than burrowing underground, and can run faster and hop higher than their rabbit cousins (necessary adaptations for escaping from predators on open ground). Rabbits, by contrast, comprise about two dozen species spread out over eight different genera, and prefer to live in shrubs and forests, where they can burrow in the ground for protection. Bonus fact: the North American jackrabbit is actually a hare! (You may wonder where "bunny" fits into all this nomenclature; this word once referred to juvenile rabbits, but now is applied indiscriminately to rabbits and hares alike, especially by children.)

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Butterflies and Moths

A monarch butterfly. Getty Images

Compared to some of the other animals on this list, the differences between butterflies and moths are pretty straightforward. Butterflies are insects of the order Lepidoptera equipped with relatively large, colorful wings that fold up straight over their backs; moths are also lepidopterans, but their wings are smaller and more drably colored, and when they're not flying they usually hold their wings close to the front of their abdomens. As a general rule, butterflies prefer to venture out during the day, while moths prefer dusk, dawn, and nighttime. Developmentally speaking, however, butterflies and moths are virtually identical: both of these insects undergo metamorphosis into their adult stages, butterflies in a hard, smooth chrysalis and moths in a silk-covered cocoon.

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Possums and Opossums

A Virginia opossum. Wikimedia Commons

This is a confusing one, so pay attention. The North American mammals known as opossums are marsupials of the order Didelphimorphia, accounting for over 100 species and 19 genera. (Contrary to popular belief, marsupials don't only live in Australia, though this is the only continent where these pouched mammals have evolved to large sizes.) The trouble is that American opposums are often referred to as "possums," which causes them to be confused with tree-dwelling marsupials of Australia and New Guinea of the the suborder Phalangeriformes (and which, wouldn't you know it, are also called "possums" by natives). Aside from their names, though, you're unlikely to confuse an Australian possum with an American opossum; for one thing, the former marsupials are distant descendants of Diprotodon, a two-ton wombat of the Pleistocene epoch!

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Alligators and Crocodiles

A saltwater crocodile. Getty Images

Alligators and crocodiles comprise separate branches of the reptilian order Crocodylia, Alligatoridae and Crocodylidae (we'll leave it to you to guess which is which). As a general rule, crocodiles are bigger, meaner, and more widespread: these semi-marine reptiles inhabit rivers worldwide, and their long, narrow, tooth-studded snouts are ideally shaped for snagging prey that wanders too close to the water's edge. Alligators, by contrast, have blunter snouts, less aggressive dispositions, and far less diversity (there are only two alligator species—the American alligator and the Chinese alligator—compared to over a dozen types of crocodiles). Crocodiles also have a much deeper evolutionary history than alligators; their ancestors include multi-ton monsters like Sarcosuchus (also known as the SuperCroc) and Deinosuchus, which lived alongside the dinosaurs of the Mesozoic Era.

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Donkeys and Mules

A donkey. Wikimedia Commons

This one all comes down to genetics, pure and simple. Donkeys are a subspecies of genus Equus (which also includes horses and zebras) that descend from the African wild ass, and were domesticated in the near east about 5,000 years ago. Mules, by contrast, are the offspring of female horses and male donkeys (subspecies of Equus are capable of interbreeding), and they are completely sterile—a female mule can't be impregnated by a male horse, donkey or mule, and a male mule can't impregnate a female horse, donkey or mule. Appearance-wise, mules tend to be larger and more "horse-like" than donkeys, while donkeys have longer ears and are generally considered cuter.  (There is also an equine called a "hinny," which is the offspring of a male horse and a female donkey; hinnies tend to be slightly smaller than mules, and are occasionally capable of breeding.)

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Frogs and Toads

A green tree frog. Getty Images

Frogs and toads are both members of the amphibian order Anura (Greek for "without tails.") The differences between them are pretty much meaningless to taxonomists, but popularly speaking, frogs have long hind legs with webbed feet, smooth (or even slimy) skin, and prominent eyes, while toads have stubby bodies, dry (and sometimes "warty") skin, and comparatively short hind legs. As you may have already surmised, frogs are usually found near water, while toads can range for longer distances inland, since they don't constantly need to keep their skin moist. However, frogs and toads do share two important characteristics in common: as amphibians, they both need to lay their eggs in water (frogs in circular clusters, toads in straight lines), and their hatchlings pass through a tadpole stage before developing into full-grown adults. 

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Leopards and Cheetahs

The Amur leopard. Getty Images

Superficially, cheetahs and leopards look a lot alike: both are tall, slim, rangy cats that live in Africa and the near east and are covered with black spots. But they actually are quite different species: cheetahs (Acinonyx chubatus) can be distinguished by the black "tear lines" running down the corners of their eyes and past their noses, as well as their longer tails, lankier builds, and top speeds of close to 70 miles per hour when running down prey. By contrast, leopards (Panthera pardus) have bulkier builds, larger skulls, and more complex spot patterns (which provide camouflage and may also facilitate intra-species recognition). Most importantly, you won't have to be Usain Bolt to stand any chance of escaping a hungry leopards, as these cats hit top speeds of barely 35 miles per hour, about half as fast as their cheetah cousins.

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Seals and Sea Lions

A sea lion. Wikimedia Commons

When it comes to distinguishing between seals and sea lions, the main things to consider are size and cuteness. While both of these animals belong to the family of marine mammals known as pinnipeds, seals are smaller, furrier, and have stubbier front feet, while sea lions are bigger and noisier, with elongated front flippers. Sea lions also tend to be much more social, sometimes congregating in groups of over a thousand individuals, while seals are comparative loners and spend more time in the water (the only time you're likely to find a group of seals together is when it's time to mate). Perhaps most important, since sea lions are capable of "walking" on dry land by rotating their hind flippers, and are more vocal than seals, they are the go-to pinnipeds for circuses and aquariums, where they can be taught crowd-pleasing tricks.