This list includes 15 Big animals that start with O, from “Arabian Oryx” to “Scimitar Oryx”. These entries are large vertebrates defined by adult mass or length, including mammals, birds, reptiles, and fish. Use this list for quick reference, classroom activities, or to build engaging A–Z wildlife content.
Big animals that start with O are large species whose common names begin with the letter O. The Arabian Oryx is a notable example, once extinct in the wild and later reintroduced by conservation programs.
Below you’ll find the table with Common name, Scientific name, Primary habitat (biome + region), and Typical wild lifespan (years).
Common name: The everyday name helps you quickly identify each species and match it to field guides or classroom materials.
Scientific name: The Latin name lets you confirm exact species identity and find authoritative descriptions and range information worldwide.
Primary habitat (biome + region): This shows the main ecosystem and geographic area, so you understand where each animal lives.
Typical wild lifespan (years): Estimates the average adult lifespan in the wild, helping you compare longevity across different species.
Big animals that start with O
| Common name | Scientific name | Typical adult size (mass/length) | Primary habitat (biome + region) |
|---|---|---|---|
| Okapi | Okapia johnstoni | 200–350 kg; 2.5 m | Tropical rainforest — Central Africa |
| Orangutan | Pongo pygmaeus | 50–100 kg; 1.4 m | Tropical rainforest — Borneo |
| Orca | Orcinus orca | 3,000–5,400 kg; 6–8 m | All oceans — Global |
| Ostrich | Struthio camelus | 90–145 kg; 2.8 m (height) | Savanna and semi-desert — Africa |
| Ocean Sunfish | Mola mola | 250–1,000 kg; 1.8 m | Temperate and tropical oceans — Global |
| Oarfish | Regalecus glesne | ~270 kg; 3–8 m | Deep ocean (mesopelagic) — Global |
| Onager | Equus hemionus | 200–260 kg; 2.1 m | Desert and semi-desert — Asia |
| Olive Baboon | Papio anubis | 22–37 kg; 0.7 m | Savanna, forest, grassland — Equatorial Africa |
| Ocelot | Leopardus pardalis | 8–18 kg; 0.7–1.0 m | Tropical forest and scrubland — The Americas |
| Oribi | Ourebia ourebi | 12–22 kg; 0.9–1.1 m | Grassland and savanna — Sub-Saharan Africa |
| Arabian Oryx | Oryx leucoryx | 65–75 kg; 1.6 m | Desert and arid plains — Arabian Peninsula |
| East African Oryx | Oryx beisa | 150–200 kg; 1.6–1.9 m | Semi-desert and savanna — Horn of Africa |
| Scimitar Oryx | Oryx dammah | 140–210 kg; 1.6–2.4 m | Arid plains and desert — North Africa |
| Olive Ridley Sea Turtle | Lepidochelys olivacea | 35–50 kg; 0.7 m (carapace) | Tropical oceans — Global |
| Ornate Wobbegong | Orectolobus ornatus | ~50 kg; up to 2.9 m | Coral reefs and coastal waters — Western Pacific |
Descriptions
Okapi
The only living relative of the giraffe, famous for its zebra-like striped hindquarters. Lifespan is around 20–30 years. This elusive forest dweller was unknown to science until the 20th century and is now Endangered.
Orangutan
One of the largest arboreal (tree-dwelling) mammals, known for its long arms and shaggy, reddish-brown hair. Lifespan is 35–45 years in the wild. Bornean orangutans are Critically Endangered due to habitat loss.
Orca
Also known as the killer whale, the orca is the largest species of dolphin and a highly intelligent apex predator. Lifespan can be 50–80 years. Orcas live in complex social groups called pods and have diverse hunting methods.
Ostrich
The world’s largest and heaviest bird, unable to fly but capable of running at speeds up to 70 km/h (43 mph). Lifespan is 30–40 years. Its powerful legs can deliver formidable kicks for defense.
Ocean Sunfish
The heaviest known bony fish in the world, recognized by its massive, flattened, disc-like body. Lifespan in the wild is unknown but estimated at over 20 years. It primarily feeds on jellyfish and other gelatinous zooplankton.
Oarfish
The world’s longest bony fish, its serpentine body and rare sightings are thought to be a source of sea monster myths. Its lifespan is unknown. It has a distinctive red, mane-like dorsal fin.
Onager
A species of wild ass known for its incredible stamina and speed, capable of reaching nearly 70 km/h (43 mph). Lifespan is around 20–25 years. It is better adapted to desert life than most other large herbivores.
Olive Baboon
Named for the olive-green tint of its coat, it’s one of the most widespread baboon species. Lifespan is 20–30 years. They live in large, socially complex troops that can number over 100 individuals.
Ocelot
A medium-sized wild cat with a striking spotted and striped coat that provides excellent camouflage. Lifespan is around 10 years in the wild. Despite its relatively small size, it can prey on animals larger than itself.
Oribi
A graceful, slender antelope with long legs and a short black-tipped tail. Lifespan is 8–12 years. When alarmed, it often hides until the last moment before bursting from cover in a bounding run.
Arabian Oryx
A stunning desert antelope with a white coat and long, straight horns. Lifespan is around 20 years. It was declared Extinct in the Wild in 1972 but was saved by a successful captive breeding and reintroduction program.
East African Oryx
A large, powerful antelope with impressive, spear-like horns and distinctive black-and-white facial markings. Lifespan is 18–20 years. It is exceptionally well-adapted to survive in hot, arid environments.
Scimitar Oryx
Named for its long, curved horns, this oryx is now classified as Extinct in the Wild. Lifespan is ~20 years. Massive international efforts are underway to reintroduce herds from captive populations back into their native range.
Olive Ridley Sea Turtle
The most abundant sea turtle, named for the olive color of its heart-shaped shell. Lifespan is around 50 years. It is famous for its synchronized mass nesting events, known as “arribadas.”
Ornate Wobbegong
A master of camouflage, this flat-bodied carpet shark uses its weed-like skin flaps and intricate pattern to ambush fish and crustaceans. Lifespan is estimated at over 20 years. It lies motionless on the seafloor waiting for prey.