Nurse shark (Ginglymostoma cirratum) Nurse shark A slow-moving, bottom-dwelling shark of warm coastal waters. Nurse sharks feed primarily on invertebrates and small fishes, are mostly nocturnal, and are generally not aggressive t…
Nuthatch (Sitta): small tree-dwelling birds of the Northern Hemisphere Nuthatch Nuthatches (genus Sitta) are compact, acrobatic songbirds that live in temperate and boreal woodlands. They nest in tree cavities, cache seeds, and are known for climbing down trun…
Nyala: the spiral-horned antelope of southern Africa Nyala Overview of the nyala (Tragelaphus angasii), its appearance, behaviour, habitat, distribution, predators and conservation status in southern Africa.
Nyasasaurus — a fragmentary reptile that may be the earliest dinosaur Nyasasaurus Nyasasaurus is a fragmentary archosaur from Tanzania's Middle Triassic Manda Beds. Known from a few bones, it may represent the earliest dinosaur or a close relative and has altere…
Nyctibatrachus — night frogs of the Western Ghats Nyctibatrachus Nyctibatrachus is a genus of small, mostly nocturnal frogs endemic to India’s Western Ghats. Night frogs are stream-associated, include more than 30 recognized species, and are vul…
Nyctosaurus: a Late Cretaceous pterosaur Nyctosaurus Nyctosaurus was a small to medium pterosaur of the Upper Cretaceous noted for its long wings and striking cranial crest; fossils come mainly from marine deposits in North America.
Nymphalidae: the brush-footed butterflies Nymphalidae Nymphalidae is the largest family of butterflies, with roughly 6,000 species worldwide. Known as brush-footed butterflies, they show diverse colors, life cycles, ecological roles,…
Oarfish (Regalecidae): ribbonlike deep‑sea fishes and their history Oarfish Oarfish are long, ribbonlike marine fishes in the family Regalecidae. Four species exist; the giant oarfish can reach about 17 m. Pelagic and rarely seen, they are linked to sea‑se…
Obdurodon: an extinct toothed monotreme genus Obdurodon Obdurodon is an extinct genus of monotreme related to the modern platypus. Fossils show adult teeth and a suite of features that help reconstruct early platypus evolution and diver…
Ocean sunfish (Mola mola): description, behavior, and ecological role Ocean sunfish The ocean sunfish (Mola mola) is a distinctive, very large bony fish of warm and temperate seas. This article summarizes its appearance, diet, behavior, reproduction, threats, and…
Oceanic dolphins (family Delphinidae) Oceanic dolphin Oceanic dolphins are toothed whales of the family Delphinidae. Widely distributed in seas worldwide, they are social, intelligent marine mammals with diverse species, behaviors, an…
Oceanic whitetip shark (Carcharhinus longimanus) Oceanic whitetip shark Comprehensive overview of the oceanic whitetip shark: identification, distribution, ecology, human interactions, and conservation measures.
Ocellated turkey (Meleagris ocellata) Ocellated turkey A colorful, ground-dwelling turkey native to the Yucatán Peninsula and nearby Central America, noted for iridescent plumage, eye-like tail spots, and distinctive courtship displays…
Ocelot (Leopardus pardalis): description, range, behavior and conservation Ocelot Neotropical wild cat known for its distinctive spotted coat, nocturnal habits and wide range from South America into parts of Central and North America. Covers appearance, ecology,…
Ocicat: domestic cat breed with wild-looking spotted coat Ocicat The Ocicat is a domestic cat bred to look like a wild feline without any wild ancestry. Recognized for its spotted coat, outgoing and trainable nature, it developed from Siamese, A…
Octopoda — biology, diversity and natural history of octopuses Octopoda Octopoda is the order of eight-armed cephalopods (octopuses). It includes both familiar shallow-water species and gelatinous deep-sea forms, with a fossil record extending into the…
Octopodiformes Octopodiformes are soft-bodied cephalopods including octopods and the vampire squid, notable for eight arms, advanced behaviour, and adaptations to a wide range of marine habitats.
Octopus: biology, behavior, and relationship with humans Octopus An accessible encyclopedia entry on octopuses covering anatomy, behavior, habitat, reproduction, diversity and their interactions with people and ecosystems.
Odonata: dragonflies and damselflies Odonata Odonata is the insect order that includes dragonflies and damselflies. This article explains their anatomy, life cycle, evolution, behavior, ecological roles and conservation conce…
Odontoceti: the toothed whales — biology, behaviour, and diversity Odontoceti Odontoceti (toothed whales) are a suborder of cetaceans including dolphins, porpoises and sperm whales; they use teeth and echolocation to hunt a range of prey and form complex soc…
Odontochelys — early toothed turtle with a half-shell (Triassic) Odontochelys Triassic toothed turtle from Guizhou, China. Retains a plastron but lacks a full carapace, offering insight into turtle shell evolution and prompting debate about primitive versus…
Okapi (Okapia johnstoni) — Central African forest giraffid Okapi The okapi is a shy, forest-dwelling mammal in the giraffe family, native to Central Africa. It is known for zebra-like leg stripes, a long prehensile tongue, solitary habits and th…
Old Major (Animal Farm) Old Major is the elderly prize boar whose ideas spark the rebellion in George Orwell's Animal Farm; he symbolizes the founders of revolutionary ideology and introduces themes of eq…
Old World Flycatchers (family Muscicapidae) Old World flycatcher Overview of Old World flycatchers (Muscicapidae): small insect-eating passerines native to Europe, Asia and Africa, their traits, classification, behaviour and ecological role.
Old World monkeys (Cercopithecidae): diversity, behaviour and conservation Old World monkey Overview of Old World monkeys (Cercopithecidae): distribution across Africa and Asia, physical traits, social systems, ecology, notable species and conservation concerns.
Old World vulture Large scavenging birds of the Old World (Africa, Europe and Asia) in the family Accipitridae; visually oriented scavengers with distinct adaptations and important ecological roles.
Old World warbler Informal name for a diverse group of small insectivorous passerine birds once placed in Sylviidae; modern research has split them into multiple families and clarified relationships…
Oligochaete — segmented worms of the class Clitellata Oligochaete Oligochaetes are a diverse group of segmented annelid worms (around 10,000 species) that include earthworms. They have few bristles, a clitellum, and play key roles in soil and fre…
Olinguito (Bassaricyon neblina): a cloud‑forest mammal of the Andes Olinguito A small, nocturnal, arboreal mammal of the Andes cloud forests. Described in 2013, the olinguito (Bassaricyon neblina) belongs to Procyonidae and was recognized through museum spec…
Olm (Proteus anguinus): the European cave salamander Olm The olm (Proteus anguinus) is a blind, aquatic salamander of the Dinaric karst. This subterranean amphibian is notable for paedomorphosis, slow metabolism, specialized cave adaptat…
Olorotitan — a crested hadrosaur from the Late Cretaceous Olorotitan Olorotitan is a crested lambeosaurine hadrosaurid from the Late Cretaceous Russian Far East, known from a largely complete skeleton and notable for a tall hollow crest and typical…
Omul — the Baikal whitefish (endemic omul of Lake Baikal) Omul Omul is a whitefish of the salmon family found only in Lake Baikal and its tributaries. Valued locally for its flavor, it has cultural, ecological, and economic importance in the B…
Onager (Equus hemionus): the Asian wild ass Onager Onager, or Equus hemionus, is a wild ass native to parts of Asia. This article summarizes its appearance, behavior, range, conservation concerns and how it differs from other equid…
Oncilla (Leopardus tigrinus): small spotted Neotropical wild cat Oncilla The oncilla is a small, elusive spotted cat of Central and South America. This article covers its appearance, behavior, range, taxonomy issues, threats from habitat loss, and conse…
Opabinia — a strange Cambrian animal with five eyes Opabinia Opabinia regalis is a small, extinct Cambrian animal from the Burgess Shale known for its five dorsal eyes and a flexible proboscis; its odd anatomy has informed debates about earl…
Ophthalmosauridae: the large‑eyed ichthyosaur family Ophthalmosauridae Ophthalmosauridae were a worldwide family of ichthyosaurs from the Middle Jurassic to the mid‑Cretaceous, notable for very large eyes and marine adaptations for active swimming and…
Ophthalmosaurus — a large-eyed Jurassic ichthyosaur Ophthalmosaurus Ophthalmosaurus was a dolphin‑like marine reptile of the Upper Jurassic, notable for enormous eyes and adaptations for low‑light or deep hunting; well‑preserved fossils are known f…
Harvestmen (Opiliones): Biology, Diversity, Fossils, and Ecology Opiliones Overview of harvestmen (Opiliones): anatomy and how they differ from spiders, global diversity and fossil history, feeding and ecological roles, and interactions with people.
Opisthocoelicaudia: a Late Cretaceous Mongolian titanosaur Opisthocoelicaudia Opisthocoelicaudia is a titanosaurian sauropod from Mongolia's Nemegt Basin, known from a largely complete skeleton lacking the skull; it is important for studies of Asian Late Cre…
Opossum (Didelphimorphia): biology, behavior, and ecological role Opossum An accessible overview of opossums: their classification, appearance, behavior, reproduction, ecological benefits (including tick control), differences from Australian possums, and…
Orange-breasted sunbird (Anthobaphes violacea) Orange-breasted sunbird A compact, nectar-feeding bird endemic to southwestern South Africa, notable for the male's orange breast and its role in fynbos pollination. Taxonomy, appearance, habitat, behavio…
Orange-thighed frog (Litoria xanthomera) Orange-thighed frog A concise encyclopedia entry on the orange-thighed frog, an arboreal amphibian of north Queensland: appearance, habitat, behaviour, reproduction and conservation issues.
Orangutan (genus Pongo) Orangutan Large reddish arboreal great apes of Southeast Asia (genus Pongo). Three species inhabit Borneo and Sumatra and face severe threats from habitat loss, hunting and trade.
Oreophrynella — bush toads of the Guiana Shield tepuis Oreophrynella Oreophrynella, or bush toads, are a small genus of high-elevation true toads from the tepuis of northern South America, adapted to rocky, mossy plateaus and notable for unusual def…
Oriental Longhair A long-coated member of the Siamese-type cats, the Oriental Longhair combines a slender oriental body with a silky long coat; known for variety of colors, active temperament, and d…
Oriental magpie-robin (Copsychus saularis) Oriental magpie-robin A small, vocal passerine of South and Southeast Asia known for its black-and-white plumage, melodious song, cavity nesting habits, and cultural importance; now placed in the Old Wo…
Oriental turtle dove (Streptopelia orientalis) — overview and natural history Oriental turtle dove A compact encyclopedia entry on the Oriental (rufous) turtle dove, covering appearance, range, behavior, breeding, and relationships within the Columbidae family.
Oriole (Old World orioles, genus Oriolus) Oriole Old World orioles are colorful passerine birds of the family Oriolidae, native to Africa, Asia and Europe; they evolved in Australasia and are distinct from New World orioles.
