The letter O is packed with animal celebrities: owls that can turn their heads three-quarters of the way around, octopuses with three hearts, orcas that rule the ocean, and the opossum — North America’s only marsupial. There is even a mysterious forest animal, the okapi, that looks like a cross between a giraffe and a zebra.
This guide gathers the best O animals in one place: a quick list with one-line facts, deeper entries on wild species (with links to our full profiles), spotlight mini-profiles, a comparison table, and answers to common questions.
Common Animals That Start With O
Start with the O animals almost everyone recognizes — and a few surprises worth knowing.
- Owl — a night hunter that cannot move its eyeballs, so it turns its head as much as 270 degrees instead.
- Octopus — an eight-armed genius of the sea with three hearts and blue blood.
- Opossum — North America’s only marsupial; it really does “play dead” when terrified.
- Otter — a playful swimmer; sea otters even hold paws while sleeping so they do not drift apart.
- Orca — also called the killer whale, though it is actually the largest member of the dolphin family.
- Orangutan — Asia’s only great ape; its name means “person of the forest” in Malay.
- Ostrich — the world’s largest and fastest-running bird, sprinting over 40 miles per hour.
- Okapi — the giraffe’s only living relative, with zebra-striped legs and a velvet coat.
- Ocelot — a beautifully spotted wild cat of the Americas, about twice the size of a house cat.
- Oryx — a desert antelope with spear-straight horns that can survive weeks without drinking.
- Osprey — a fish-hunting raptor that plunges feet-first into water and rarely misses.
- Ocean sunfish — the heaviest bony fish on Earth, shaped like a giant swimming head.
- Oyster — a shellfish that can turn a grain of grit into a pearl.
- Ox — not a wild species but a trained work animal — an ox is a domestic bovine taught to pull plows and carts.
Wild Animals That Start With O
Several wild O animals have full profiles on World Deer. Here is what makes each one special, with links to keep reading.
The okapi was unknown to science until 1901 because it hides so well in the dense Ituri Forest of the Democratic Republic of the Congo. It has a long blue-black tongue — like its giraffe cousins — that can reach its own ears.
The opossum is one of nature’s great survivors. Playing dead is not an act it chooses — extreme fear triggers a faint, complete with slowed breathing and a terrible smell that convinces predators to move on.
Otters are found on every continent except Australia and Antarctica. They are members of the weasel family with webbed feet, closeable ears and nostrils, and some of the densest fur in the animal kingdom.
The orca is the ocean’s true apex predator — even great white sharks leave an area when orcas arrive. Pods have their own dialects of clicks and calls, passed down like family traditions.
Some orca populations are so distinct that scientists study them separately. Offshore orcas, for example, roam far from land and grind their teeth down eating rough-skinned sharks.
Owls hunt with astonishing hearing: a barn owl can catch a mouse in total darkness by sound alone, because one ear opening sits slightly higher than the other, letting the owl pinpoint exactly where a rustle came from.
The orangutan spends more time in trees than any other great ape, building a fresh leafy sleeping nest every single night. Mothers teach their young for seven to eight years — one of the longest childhoods of any animal.
The ostrich cannot fly, but its two-toed legs are fearsome tools — a single kick can injure a lion. And no, it does not bury its head in the sand; it lies flat and still to hide.
More O Animals Worth Knowing
A few more O animals worth adding to your list, from caves to open ocean.
- Olm — a pale, blind cave salamander from Europe that can live decades and go years between meals.
- Oarfish — the longest bony fish in the sea — a ribbon-shaped deep-sea giant that can exceed 25 feet.
- Onager — a wild ass of Asian deserts, one of the fastest members of the horse family.
- Olive baboon — a savanna primate that lives in complex troops of up to 100 or more.
- Ocellated turkey — a jewel-colored turkey found only around Mexico’s Yucatán Peninsula.
- Oystercatcher — a shorebird with a bright orange, chisel-like bill for opening shellfish.
- Orb-weaver spider — the master architect behind the classic round, spiraled spiderweb.
Spotlight: O Animals We Cover in Depth
Okapi: The Forest Giraffe Almost Nobody Sees
The okapi looks like a mashup of three animals — horse body, zebra legs, giraffe head — but it is 100 percent its own species, and the giraffe’s only living relative. Its oily, velvety coat sheds rain in its damp rainforest home.
Okapis are so shy that researchers mostly study them through camera traps. Learn how they communicate in sounds too low for humans to hear in our okapi profile.
Opossum: The Backyard Marsupial
The Virginia opossum carries up to a dozen bee-sized babies in her pouch, then gives the growing youngsters rides on her back. Opossums are also surprisingly helpful neighbors: they eat ticks, snails, and garden pests.
They are highly resistant to snake venom and almost never carry rabies, thanks to a low body temperature. Meet this misunderstood animal properly in our opossum guide.
Orca: The Ocean’s Smartest Hunter
Orcas live in family pods led by grandmothers who may reach 80 or 90 years old. Different populations hunt differently — some make waves to wash seals off ice floes, while others herd herring into tight balls.
A male’s dorsal fin can stand six feet tall, as tall as an adult human. Start with our orca overview, then meet the offshore orcas that specialize in sharks.
O Animals at a Glance
Ten O animals at a glance — from the rainforest floor to the open ocean.
| Animal | Type | Habitat | Fun fact |
|---|---|---|---|
| Owl | Bird of prey | Worldwide except Antarctica | Can rotate its head about 270 degrees |
| Octopus | Cephalopod | Oceans worldwide | Has three hearts, nine brains, and blue blood |
| Opossum | Marsupial | North and Central America | Faints and “plays dead” when badly frightened |
| Otter | Mustelid | Rivers, lakes, and coasts | Sea otters hold paws while sleeping to stay together |
| Orca | Marine mammal | Every ocean on Earth | Actually the largest species of dolphin |
| Orangutan | Great ape | Borneo and Sumatra rainforests | Builds a brand-new treetop nest every night |
| Ostrich | Bird | African savannas | Its eye is bigger than its brain |
| Okapi | Mammal | Congo rainforest | Giraffe relative with a tongue long enough to wash its ears |
| Ocelot | Wild cat | American forests and scrub | Every ocelot’s spot pattern is unique |
| Oryx | Antelope | African and Arabian deserts | Can go weeks without drinking water |
Frequently Asked Questions
What is the biggest animal that starts with O?
The orca, which can grow about 30 feet long and weigh up to around 10 tons. Despite the nickname “killer whale,” orcas are dolphins — the biggest dolphins in the world — and there is no record of a wild orca killing a human.
Do opossums really play dead?
Yes, but they cannot help it. When an opossum is terrified, its body faints automatically: it flops over, breathes slowly, and releases a rotten smell. Predators think it is spoiled food and leave. Minutes or hours later, it wakes up and walks away.
Why do owls turn their heads so far around?
Because their eyes are fixed in their skulls like telescopes — they cannot roll them the way we can. To look around, an owl swivels its whole head up to 270 degrees, using extra neck bones (14 instead of our 7) and special blood vessels that keep blood flowing.
Keep Exploring the Alphabet
Keep the alphabet adventure going — the master index has every species profile on the site, and the previous letter is one click away.
- Animals A–Z — the master index of every species profile on World Deer
- Animals That Start With N — the previous stop on our alphabet tour
