The quokka - one of the most smiling animals in the world, is a pint-sized mammal endemic to Australia's offshore islands and distantly related to kangaroos and wallabies, is almost always happy. To see these cute beasts in action, simply scroll through the amusing photographs collected in the viral hashtag "#quokkaselfie." But why are they smiling? According to Arizona State University researchers, the quokka's joyful appearance is a result of evolution — sort of the inverse of the "resting brat face."

Quokkas are herbivores, which means they eat flora and roughage to keep their pearly whites sparkling - a tactic that also helps to keep human teeth cleaner and looking better. And, quokkas enjoy junk food, prompting officials to warn visitors to Rottnest Island not to give the quokkas parts of sandwiches. Bread becomes lodged between their teeth and, because quokkas cannot floss, feeds germs that can cause a severe or even fatal illness.

Chimps have a dentition comparable to humans in that they have the same number of teeth, the same location and kind of teeth, and the same pattern of having baby teeth that fall out to make way for permanent adult teeth. Chimpanzees, like us, grin to express a wide variety of emotions, from fear to enjoyment. Of course, there are certain distinctions between a chimp's and a human's grin.

For one thing, chimpanzees (and other primates) are more likely to grin while threatening or showing danger. This might be because their canines are significantly bigger. However, there are more parallels than differences, particularly when it comes to the upkeep of these adorable beasts' grins. Chimpanzees maintain their dazzling whites using instruments that keep them healthy and clean. Chimps have been spotted brushing their teeth and picking food from between their teeth using adapted sticks.

Dogs don't grin on their own; they do it because they sense your enjoyment. Over the decades, man's best friend has evolved the capacity to pick up on indications provided by body language and respond in kind, even flashing people a pleased, tooth-baring grin. Canines in the wild expose their teeth to show hostility or fear. When they think you're about to throw a ball or give them a reward, they'll enthusiastically grin to indicate their delight and anticipation.

However, one of our most common companion animals needs as much or more dental care than people do, and vets are eager to help. Adult dogs have 42 permanent teeth, and more than 80% of puppies exhibit early indications of periodontal disease by the age of three.

The laughing kookaburra is a symbol of Australia's birdlife as well as the inspirational "merry, merry king of the bush" from a children's song.

The laughing kookaburra is the biggest member of the Kingfisher family, with females weighing up to one pound and growing to 18 inches in length. It is native to the eucalyptus forests of eastern Australia. The laughing kookaburra's wing plumage is dark brown, with a white head and underbelly. It has dark brown eye stripes across its face and a black top bill. It has a reddish-colored tail with black bands.

Monogamous, territorial Laughing Kookaburras build their nests in tree holes. Females deposit one to five eggs, which are cared for by a group of parents and older siblings. Fledgling kookaburras usually stay with their parents to assist with the care of the next clutch.

One of the smiling animals on this list is the crow. Crows are noted for their cunning and their harsh, rasping caws. These fascinating birds can learn to imitate human vocal intonations. They also recall which individuals treated them well and which ones did not. Even more astounding is the fact that they transmit this knowledge down to their offspring.

Crows have been recorded pulling pranks on each other and engaging in complex forms of play, according to scientists. All for fun, they'll hang from trees, slide down inclines, and conceal stuff from each other.

Crows are gregarious and cooperative creatures. When they're not deceiving one another, they're teaching young crows important lessons. Male crows will roost together in a sort of bird bachelor pad before finding a mate.

Donkeys are playful and clever creatures who know how to make the most of each day. They like grooming and interacting with one another. In fact, if they're alone, they'll get melancholy, but if they have some goat pals to hang out with, they'll cheer up.

Donkeys may be found all throughout the world, but they thrive in arid environments. Wild donkey herds can be found in the United States, northern Africa, and the Middle East. Donkeys are known for their obstinacy, yet this obstinacy is an indication of their intelligence. If they believe it is hazardous, donkeys refuse to go anywhere.

Wild donkeys may be seen in the Nevada and California deserts. In Greece, Agia Marina is a refuge for domestic donkeys. The Donkey Sanctuary in Sidmouth, England, is a sanctuary for donkeys, operates donkey rescues around the world.

Several dolphin species have sexual dimorphism, which means that males are bigger than females. They have streamlined bodies and flippers on two of their limbs. These pleasant sea creatures appear to be smiling or laughing all the time, which makes us wonder what the joke is. As they leap through the air and into the water, dolphins have a terrific time.

Dolphins are among the most intelligent creatures on the planet. They've mastered the use of tools and created sophisticated communication systems with one another. They are also compassionate creatures. Dolphins will not abandon injured or weak members of their group; instead, they will assist them in reaching the surface and obtaining food.

These social, clever, and sympathetic creatures have a wonderful existence, which explains their constant smile.

These social, joyful animals are entertaining to watch, whether they're wild goats sprinting up a steep mountain or domestic goats dancing in a farm area. They are difficult to resist because of their clever tinier features, short beards, and prancing motions. Goats, contrary to popular belief, are clean creatures who prefer clean food over waste. They aren't very choosy about what they eat, though, and will try everything.

Because goats are so quiet and joyful, they are sometimes used as "therapy goats" to calm nervous horses. Goats are used in "goat yoga" studios to increase the soothing benefits of yoga.

Although domestic goats are not endangered, several wild goat species are. The Oakland Zoo has pygmy wild goats on display. Nigerian dwarfs and San Clemente Island goats may be seen at the Smithsonian Zoo in Washington, D.C.

Being one of the most sociable animals in the world, squirrels are tenacious survivors who exist in every part of the globe as the second most intelligent rodents (after rats). Squirrels have adapted to life in suburban and urban areas, and they play a vital role in these ecosystems.

Squirrels appear to spend their days chasing each other, searching for food, hiding it, and jumping between tree branches. These small fellas don't seem to be able to sit still. When you observe them in your yard or in a city park, they may keep you entertained for hours.

Chipmunks, groundhogs, and prairie dogs are all members of the squirrel family. These are all joyful creatures in their own way, but squirrels win for constantly appearing to be having a good time.

Cockatoos, like other birds and parrots, do not have teeth, but their beaks must be kept in excellent working order. Birds with healthy beaks will grind them on their own. The large crests and bent bills distinguish cockatoos. Their plumage is often less colorful than that of other parrots, consisting primarily of white, gray, or black, with contrasting colors in the crest, cheeks, and tail.

Cockatoos prefer seeds, tubers, corms, fruit, flowers, and insects. They frequently forage in big flocks, especially while grazing on the ground. Cockatoos are monogamous and build their nests in tree cavities. Some cockatoo species have Some species have suffered as a result of habitat loss, particularly due to a scarcity of appropriate nesting hollows when huge old trees have been felled. On the other hand, some species have adapted well to human alterations and are considered agricultural pests.