Our planet is filled with animals that come all over the place, all different environments, and with walks of life that are completely unique to their species.
Just because an animal may start with the same letter as another doesn’t mean they’ll share any other similarities.
There are all different types of animals that have names that begin with the 15th letter of the alphabet.
75 Animals That Start With O
The octopus is often the first choice for adults and children when thinking of animals that can represent the letter O.
These popular sea creatures have three hearts, only one of which is pumping blood to the octopus’s organs while the other two hearts provide oxygenated blood to the octopus’s gills.
The heart that pumps blood to the organs stops when the octopus is swimming because it is too exhausting for the octopus to have all three hearts pumping.
Many people think that an okapi looks like a weird zebra, but they are actually the only living relatives of giraffes.
These creatures can rarely be found in their native homeland of the Ituri Forest thanks to the heightened sense of hearing and extremely skittish nature.
Their ears are capable of rotating independently, which allows them to hear from many directions.
3. Orange Fiddler Crab
Like other fiddler crabs, the orange fiddler crab is known for its comically uneven claws.
However, it is only the males that have the uneven claws, with their dominant claws capable of growing to nearly double the length of their bodies.
Orange fiddler crabs are known to bury themselves over 1.5 feet underground.
When they aren’t hiding in their burrows, they can be found walking along the bottom of lagoons and on shores with plenty of boulders.
The oryx is one of the most common antelopes that you will find in zoos, even if they may longer be as common in the wild.
There are six different types of oryx, such as the Scimitar-Horned and Arabian oryx.
The name comes from the Greek word for “pickaxe”, in reference to the shape of oryx’s horns and the way that they use their horns in play or fights.
Opossums, commonly referred to as possums in the United States, are quite intelligent creatures.
When testing the intelligence of different animals, opossums ranked higher than rats, rabbits, dogs, or even cats.
While opossums are best known for playing dead, they actually have multiple tactics for running away that they will use before they decide to play dead.
These tactics include growling, belching, urinating, or even defecating.
6. Owens Pupfish
The Owens pupfish is an endangered species of fish that can only be found in five populations in Owens Valley, California.
This fish could once be found in every spring pool, irrigation ditch, slough, flooded pasture, and swamp in the valley.
When invasive species such as non-native bass and trout were introduced to the area, they caused an intense amount of damage to the rare specie’s population.
Fish, like the largemouth bass, acted as a predator and competitor for space and food.
7. Oxford Sheep
Oxford sheep have been raised for generations by farmers for their fine wool in England.
However, the breed didn’t have any standards or an actual name until 1859.
This was the same time that farmers began to sell their sheep to farmers in other countries.
Although these sheep are known best for their wool, they are also bred for their meat.
These large sheep are some of the heaviest sheep, due to the density of their wool.
This makes them the perfect sheep for colder climates.
8. Ornate Spiny Lobster
The ornate spiny lobster, also known as the ornate crayfish, is one of the largest species of crayfish.
They are capable of growing up to 20 inches in length.
These nocturnal hunters will prey on mollusks, worms, and smaller crustaceans.
During the day, groups of ornate spiny lobsters can be found in underwater caves and crevices.
Otterhounds have been by our sides since medieval times, when they were once bred to hunt otters.
While otter hunting may have been banned, otterhounds have found a new job as an excellent family pet.
On average, females are two feet tall, but males are capable of getting much larger.
Otterhounds weigh about 80 pounds to 115 pounds.
10. Omura’s Whale
Omura’s whales are smaller, thin whales that will have singing battles for their mates.
If multiple male Omura’s whales are in an area near a female, they will try to drown out each other’s songs.
These musical fights can go on for hours.
This whale was first described in 2003, but they were not recognized in the wild until recently in 2015.
11. Okarito Kiwi
Okarito kiwis are some of New Zealand’s most famous, flightless birds.
Kiwis look exactly like the fruit they’re named after.
An Okarito kiwi can live from 38 years to 48 years.
No matter their age, kiwis have terrible eyesight.
They use their sense of smell to help guide them instead.
There are four different types of oysters that are separated by different traits, such as whether they’re edible or the type of shell they have.
True oysters are only ones that are collected to be eaten.
Pearl oysters include any oyster that is capable of creating pearls.
Thorny oysters are the oysters with pointy shells.
Saddle oysters have incredibly thin shells compared to the other type of oysters.
13. Orange-Breasted Falcon
The orange-breasted falcon is a rare bird of prey that can only be found in the Maya Mountains and the Mirador Cordillera in Central America.
These birds rely on cliffs to provide a safe place to build their nests and raise their young.
Orange-breasted falcons raise their young for three times longer than any other falcon.
14. Oxyrhyncha Mantis Shrimp
The oxyrhyncha mantis shrimp, also known as the praying mantis shrimp, is known to stand on its back legs and lift its pincers like the bug.
This shrimp is not afraid to fight anything that comes within its pincers’ reach.
They have even been known to nip swimmers and divers who get too close.
15. Orange Thighed Tree Frog
The orange thighed tree frog can be found deep in the rainforests of Queensland, Australia.
These tree frogs are able to grow up to 2.2 inches.
When looking for a mate, the males will sing out in chorus for nine to 12 hours at a time.
The rainy breeding season is the only time these frogs come down from their trees.
Oxen are the largest animal that calls Greenland home, although they have been bred on farms all over the world for countless generations.
The musk ox is found natively in Greenland and is one of the wooliest breeds of oxen on the planet.
Their hair is so thick that it guards against the cold and predators.
The ‘Ō’ū is a critically endangered species of seabird that can only be found in Hawaii.
While habitat loss and an increase of new predators caused by human expansion has played a role in their population drop, the largest threat comes from mosquitos that carry different avian diseases.
No one is certain that the bird can still be found because it hasn’t been seen since the Upper Waikākea Forest Reserve, once a popular spot to find the ’Ō’ū, was hit by multiple natural disasters.
18. Oregon Spotted Frog
Oregon Spotted Frogs are medium-sized frogs that can grow to be anywhere from 1.74 inches to four inches.
Females are normally much larger than the males.
They’re normally brown or olive with plenty of black spots covering them.
As they get older, they become redder around the abdomen, and that red hue will eventually spread all over the frog’s body.
Ospreys are raptors that can be found all over the world and love to eat fish.
Their love of fish has earned them the local names of fish eagle, fishhawk, or seahawk.
Unlike other birds of prey, ospreys have incredibly arched wings, which may make them look like seagulls from a distance.
These birds are able to capture fish that measure as large as half of the bird’s wingspan or more.
20. Oriental Weatherfish
Oriental weatherfish were once exclusive to the fresh waters of Eastern Asia.
However, they have become an invasive species that has spread all over the world.
Their eel-like bodies can reach 11 inches but are normally smaller.
Females are noticeably larger than males and are the only ones to ever reach such lengths.
Although orcas are known as killer whales, they’re actually the largest member of the dolphin family.
Orcas were originally called killer whales by ancient sailors because biology had not advanced enough to tell the difference between a small whale and a massive dolphin.
They’re also incredibly fast swimmers that can reach speeds of more than 33 miles per hour and are known for being incredibly intelligent.
22. O’Shaughnessy’s Chameleon
The O’Shaughnessy’s chameleon can only be found in Madagascar and was named after the British poet Arthur O’Shaughnessy, who also happened to be a herpetologist.
Like many other chameleons, their populations are dwindling in the wild due to habitat loss and the illegal pet trade.
While it is completely legal to own one of these chameleons, it is illegal to take them from their natural habitat and keep or sell them as pets.
Ocelots get their name from the Aztec word tlalocelot, which means field tiger.
These cats can be found from South America to southern North America.
You can even find them as far north as Arizona and Texas.
These cats can live in a vast variety of environments, such as savanna grasslands, coastal marshes, mangrove forests, and even tropical forests.
24. Orange-Bellied Leafbird
The orange-bellied leafbird can be found in Yunnan, the Himalayas, and the northern parts of Southeast Asia.
These brightly colored birds are able to eat insects and spiders, but they are also able to consume nectar.
Using the roots and fibers they can find around them, they build nests suspended from twigs by their edges.
These birds prefer to keep their nests at the very ends of tree branches.
25. Olive Sea Snake
Olive sea snakes are the most common sea snakes found near the coral reefs off the northern coast of Australia.
These highly venomous snakes rarely bite humans, but their bites are fatal when they do decide to attack.
They’re able to grow well over six feet in length and will normally hunt at night.
Olive sea snakes are incredibly curious creatures that will come up to divers to figure out what they are.
Unlike divers with proper gear, olive sea snakes have to surface every two hours for oxygen.
26. Ozark Big-Eared Bat
The Ozark big-eared bat is aptly named for its massive ears, which can grow to be between 1.2 inches and 1.5 inches.
When these bats decide to hibernate, they may join a colony of anywhere from two bats to 135 bats.
The population of Ozark big-eared bats has been dwindling, heavily caused by human interference.
There are caves with signs that ask people not to go inside due to the Ozark big-eared bat hibernating.
Coming out too soon can cause them to freeze or starve to death.
Ovenbirds are named for the shape of their nests, which look like small, traditional ovens.
These tiny songbirds are incredibly light walkers that briskly scramble across the forest floors across North America.
The ovenbird’s favorite place to hunt is in the dead leaf piles scattered around the forest.
Inside the piles, there are plenty of spiders, beetles, and worms for the ovenbird to eat.
28. Ogilby’s Duiker
Ogilby’s duiker is a type of deer that lives in the high-altitude forests of Sierra Leone, Ghana, Liberia, Nigeria, Bioko Island, and even Gabon.
At maximum, Ogilby’s duiker can weigh up to 44 pounds and has a shoulder height of 22 inches.
It is estimated that there are only about 12,000 left on the planet.
29. Oldenburg Horse
The Oldenburg horse has been bred since ancient times as a strong, dependable workhorse that is big enough to muscle through anything.
These horses weigh 1,700 pounds and can live for up to 30 years.
Nowadays, they are used as show and sport horses.
You can commonly see them competing in jumping and dressage.
30. Oahu Creeper
The Oahu creeper is a tropical bird that can only be found on the island of Oahu in Hawaii.
It’s easy to tell males from females thanks to their coloring and the fact that males don’t have wing bars like females.
This endangered species has lost much of its homeland to human settlement, such as popular vacationing spots and an increase in residential areas.
31. Olive Ridley Turtle
Olive Ridley turtles are the most abundant species of sea turtle in the world, but they are still a vulnerable species.
These turtles only breed in a few locations, which means that any disturbances of any of their breeding locations can have major repercussions for their population.
They can be found at the Mesoamerican Reef, the Gulf of California, the Coral Triangle, or along the coast of East Africa.
32. Old Norwegian Sheep
The Old Norwegian sheep have been bred and raised in western Norway for many generations.
Their mutton is unlike any other sheep’s meat, and their wool creates incredibly high-quality goods.
The species has managed to survive as long as it has because the ancestral people who have lived in western Norway have relied on their goats in order to survive through the winter.
33. Ornate Chorus Frog
Ornate chorus frogs can be found in grassy areas, wetlands, bogs, and woodlands all across the southeastern United States.
On average, they are only about one to 1.5 inches in size and come in a variety of colors, making them the most colorful frogs in the region.
Despite being so colorful, these frogs are quite elusive and can be hard to find outside of their breeding month.
Ornate chorus frogs will congregate at small, fresh bodies of water during the winter in order to find mates.
34. Orange-Bellied Parakeet
For the past five years, the orange-bellied parakeet has been on the verge of extinction.
In the spring of 2019, only 23 parakeets showed up at their breeding site.
After conservationists helped breed wild and captive orange-bellied parakeets, they were able to raise the number of known orange-bellied parakeets to 118.
They bred captive and wild parakeets in order to increase the gene pool and decrease the risk of disease in the birds.
Orangequits are small, round birds that can only be found in humid forests and woodlands of Jamaica.
They flutter around and gather nectar, fruit, and seeds.
Males are navy blue with a small patch of orange plumage beneath the beak.
Females are grayish-brown with a white underbelly.
Young male orangequits will look more like females until they reach two years of age.
36. Orinoco Crocodile
The Orinoco crocodile is one of the largest hunters in its environment and will hunt anything it can find, from crabs to capybaras.
Part of what makes them such great hunters is their complex social behavior.
Orinoco crocodiles have unique social interactions, well-developed responses, coordinated feeding, and a dominance hierarchy.
At their largest, they are capable of growing 16 feet.
Ostracods are small, semi-transparent crustaceans that open their hinged shells to release the eight appendages they use for scooting through the water.
They have a single eye that can be seen from the outside and looks like a black dot.
Unlike other sea creatures, ostracods don’t have gills and instead rely on a valve in their shell that filters the water for oxygen.
38. Octopus Squid
The octopus squid, also known as the Dana octopus squid, is the largest species of squid in the world and can be found in depths below 4,090 feet in any ocean.
They are capable of growing up to seven feet in length.
As they age, their octopus-like tentacles shrink until they’re nothing but stumps.
They use their tentacles to grab their prey, pull them towards their massive beaks which they then use to tear their prey apart.
39. Outstalet’s Chameleon
Outstalet’s chameleons are some of the largest chameleons, with males reaching up to 27 inches in length and females normally growing to be about one foot.
Their eyes appear larger than what can fit in their head and give them 360-degree vision.
Every 40 days, a female is capable of laying up to 60 eggs.
In order to make catching prey easier, their tongues are coated in a sticky substance and are able to suction cup their prey to their tongue.
40. Old English Sheepdog
Old English sheepdogs are smart, gentle, fluffy dogs that make excellent family and service dogs.
On average, they are at least 21 inches tall and weigh anywhere from 60 to 100 pounds.
These dogs are perfect for families with young children thanks to their watchful, friendly nature, and they love to carefully play with children and other dogs.
The Othnielia was an herbivore that could be found all over the United States during the Late Cretaceous period.
Although they were a little over 4.5 feet long, they were quite short dinosaurs, from what we know.
At this current time, there has never been a complete fossil of an Othnielia found in order to confirm more about what the dinosaur did while it was alive.
42. One-Finned Shark
The one-finned shark, or the sharpnose sevengill shark, has unique features that separate it from other sharks.
Normally, sharks will have two or three fins on their back and five gill slits, but this shark only has one fin on its back and seven gill slits.
These sharks have poisonous flesh and become aggressive when captured by humans.
Due to fisheries, the species is nearing the threat of extinction.
43. Oahu Elepaio
The Oahu elepaio is a round songbird that can only be found on the island of Oahu in Hawaii.
You can tell males and females apart through their songs.
Both males and females have softer calls and chirps, but only the males are capable of their louder shrieks.
These birds have become used to visitors on the island and are incredibly bold with humans.
44. Otago Skink
Otago skinks are one of the rarest reptiles in New Zealand and are able to grow to nearly a foot in length.
In the wild, these reptiles can live for up to 20 years.
The residents of their homeland in southern Māori call them mokomoko thanks to their distinct markings.
As soon as these lizards crawl out of their eggs, they are completely independent.
45. Ossimi Sheep
Ossimi sheep have been bred in southern Egypt for their wool, which is similar to carpet.
They are easily spotted by their light-colored coats and their brown heads.
Males will have curly horns, but the females will never grow horns.
They are also distinguishable by their massive, thick tails.
46. Ochre-Breasted Antpitta
The ochre-breasted antpitta is a tiny, plump bird that can be found on foothills everywhere from Costa Rica to Bolivia.
Their short tails add to their circular silhouette and their eyes are just as round as their bodies.
Unlike many other birds, the ochre-breasted antpitta prefers to stay low to the ground and will sit on branches that are no more than a few feet off of the ground.
Despite staying lower to the ground, their shy nature makes them incredibly hard to spot in the wild.
47. Ozark Cavefish
The Ozark cavefish is a blind, endangered fish that can only be found in the caves of Arizona, Oklahoma, and Missouri.
They are most commonly studied in the Springfield Plateau of the Ozark Highlands.
Instead of using eyes to spot their prey, the Ozark cavefish uses the motion that their prey creates in the water to locate them.
48. Oasis Hummingbird
Oasis hummingbirds were once only found in desert lowlands and foothills, but their love of flowers has led them to be found in gardens along the oceanic coasts of Ecuador, Peru, Bolivia, and Chile.
They are much larger than other hummingbirds and have a larger range than most hummingbirds.
Females may be brown, gray, and white, but males have colorful plumage under their necks that is a combination of blue and purple.
49. Oriental Shorthair Cat
The Oriental shorthair cat is best known for its odd face and inquisitive nature.
This breed is incredibly bright and curious, looking to learn all there is to know.
Oriental shorthairs are social and friendly cats that want to be wherever their people are.
These cats are known for becoming incredibly clingy with their owners.
50. Ocellated Turkey
The ocellated turkey is known for its blue head and the blue horn that is covered in orange bumps on top of its head.
These alien-looking turkeys can only be found on the Yucatan Peninsula of Mexico, Belize, and Guatemala.
During their breeding season, their skin and feathers become even brighter.
Females are attracted to males that are more brightly colored.
Otters are aquatic mammals that can be found in both freshwater and saltwater, which is what separates river otters from sea otters.
Sea otters tend to be much bigger than river otters.
River otters weigh about 10 to 30 pounds, but sea otters will weigh 45 to 90 pounds.
Sea otters eat 25% of their weight in food daily.
52. Oahu Tree Snails
There are 41 different species of snails that are referred to as Oahu tree snails, but there were once many more.
Traditional Hawaiian songs were sung about the way they would spend their days climbing up and down the tree.
All of the species of Oahu tree snails are endangered, and many are thought to be extinct.
Onagers are native to the hot deserts of Iran, where they can easily endure temperatures as hot as 120 degrees Fahrenheit.
However, these sturdy creatures are incredibly adaptable and are able to grow thick, curly fur to keep them warm.
Onagers are known for having unruly natures, which is why ancient civilizations were unsuccessful in domesticating them.
54. Ocean Sunfish
The ocean sunfish is best known for its flat, wide body and grumpy face.
These gentle creatures have massive, shark-like fins that can be mistaken for a shark from above the water.
Ocean sunfish grow to be up to 5,000 pounds, making them the heaviest bony fish in the world.
They eat algae, squid, fish, salps, and crustaceans.
The oilbirds are nocturnal birds that love to eat fruit.
Their name comes from the way that the indigenous people and early settlers of South America would take the bird’s young from their nest and render them down to get oil for cooking and lighting fires.
You can find these birds nesting in caves, where they form massive colonies of the noisy bird.
To get around in the dark, they use echolocation.
56. Oriental Fire-Bellied Toad
The Oriental fire-bellied toad has bright colors and distinctive markings, but they are also known to release a milky toxin from their skin in the wild.
They can be found natively in China and Russia, but they are commonly raised as pets.
Unlike other toads, Oriental fire-bellied toads can’t stick out their tongues.
57. Ochre-Bellied Boobook
The ochre-bellied boobook is an elusive species of hawk owl that can be found in Sulawesi, Buton, and the Peleng Islands in Indonesia.
These birds prefer to keep themselves hidden in dense vegetation during the day, but they’ll come down to hunt insects at night.
58. Ozark Hellbender
The Ozark hellbender is a large salamander that is able to grow up to two feet in length.
They’re an endangered species that can only be found in southern Missouri and northern Arkansas.
Ozark hellbenders only come out at night to hunt crayfish, small fish, and even other hellbenders.
59. Oriental Cuckoo
Oriental cuckoos have an odd way of parenting their young.
Although they spend their nonbreeding season anywhere from Australia to Malaysia, they go anywhere from Japan to Korea to breed.
As soon as the eggs are laid, the adult Oriental cuckoos will leave their young with birds of another species, such as willow warblers and chiffchaffs.
60. Ochre Mole Rat
The ochre mole rats are large rodents that can be found in the Central African Republic, Democratic Republic of Congo, Uganda, and Sudan.
They could be found in moist savannas and tropical grasslands, but they’re so critically endangered that they could be extinct by now.
61. Owen’s Chameleon
Owen’s chameleon is one of the rarest species in Central Africa and is best known for its triceratops-like horns.
Reptile enthusiasts have tried domesticating this species, but they are terminally shy.
62. Ouachita Map Turtle
The Ouachita map turtle has a sharp, rigid shell that has a tall ridge along the back.
They’re named after the river that runs from southern Arkansas to eastern Louisiana, which is where the Ouachita map turtle eats insects, dead fish, and aquatic plants.
63. Oriental White Stork
The Oriental white stork is an endangered species of stork that can only be found in Kinosaki, Japanese.
Locals love their storks dearly and call them kounotori.
Nearly all of the population is currently in captivity while they are getting help breeding, but locals have promised the Oriental white storks that they will be free once again.
Orangutans share 97% of their DNA with humans and are incredibly bright creatures.
On average, they live for about 60 years or even more.
Unlike other animals, orangutans normally only have one offspring and very rarely have two.
65. Oregon Silverspot Butterfly
Oregon Silverspot butterflies were once commonly found all over the state, but humans have expanded into their homeland and caused the population to drop drastically.
By the 1990s, there were only four colonies of these butterflies left.
Luckily, the Oregon Zoo has devoted efforts to keep the species alive successfully.
66. Olympia Pocket Gopher
Olympia pocket gophers may look cute, they’re incredibly territorial creatures.
Unless it is the breeding season, they prefer to live alone.
Females will start their own burrows nearby, but the males will disappear.
67. Ouessant Sheep
Ouessant sheep are bright, inquisitive sheep from the French island of d’Ouessant that are raised for their fine wool.
Their wool is normally turned into fine knitting yarn or soft wearing yarn.
68. Okinawa Spiny Rat
The Okinawa spiny rat is a critically endangered species that can only be found in the northern part of Okinawa, Japan.
At one point, they were thought to be extinct, but they were rediscovered in 2008.
69. Orange Fruit Dove
Orange fruit doves are brightly colored birds that have a unique call that somewhat sounds like dripping water.
Males are orange with green heads, but females are dark, navy blue with a forest green head.
70. Ornate Box Turtle
Ornate box turtles are a common choice of turtle for those who want to raise a turtle, but they are not recommended for beginners due to their slightly complex dietary and environmental needs.
With proper care, they can live for 40 to 60 years.
71. Oceanic Whitetip Shark
Oceanic whitetip sharks hunt in deep tropical or subtropical waters.
They can grow up to 11 feet in length and can live for up to 25 years.
Because they live longer, it takes these sharks longer to mature.
Ostriches are the biggest, living birds and they have the largest eyeballs of any other land animal at about two inches across.
An ostrich egg can weigh three pounds, making it the largest kind of egg currently found on the planet.
Olms are the blind, featureless amphibians that have adapted to their dark, cave environment.
Due to their coloration and human-like lifespan, they are nicknamed the “human fish”.
Olms are capable of living past 100 years old.
The Ornitholestes were carnivores that roamed the planet during the Jurassic period.
They were first found in July of 1900 in the United States.
Nobody is truly certain what the dinosaur looks like because we have only found skulls and partial postcranial pieces.
In the early days of sailing, sailors would come home raving about seeing a sea serpent when seeing these creatures.
Oarfish are the longest bony fish alive and can grow to lengths of anywhere between 45 and 50 feet.NEXT: 75 Animals That Start With Y (With Pictures)