Oak Toad
Oarfish
Ocean Perch
Ocean Pout
Ocean Whitefish
Oceanic Whitetip Shark
Ocellated Turkey
Ocelot
Octopus
Oenpelli python
Oilfish
Okapi
Old English Sheepdog
Old House Borer
Oleander Hawk Moth
Olingo
Olive Baboon
Olive python
Olive Sea Snake
Olm
Olympic Marmot
Onagadori Chicken
Onager
Opabinia
Opah
Opaleye (Rudderfish)
Opossum
Oranda Goldfish
Orange Baboon Tarantula
Orange Dream Ball Python
Orange Roughy
Orange Spider
Orange Tanager (Orange-Headed Tanager)
Orange-Crowned Warbler
Orangutan
Orb Weaver
Orchard Oriole
Orchid Dottyback
Oregon Spotted Frog
Ori-Pei
Oribi
Oriental Cockroach
Oriental Dwarf Kingfisher
Orinoco Crocodile
Ornate Bichir
Ornate Black-Tailed Rattlesnake
Ornate Box Turtle
Ornithocheirus
Ornithomimus
Ortolan Bunting
Oscar Fish
Osprey
Ostracod
Ostrich
Otter
Otterhound
Ovenbird
Oviraptor
Owl
Owl Butterfly
Owlfly (Ascalaphidae)
Ox
Oxpecker
Oyster
Oyster Toadfish
Ozark Bass