Animals

Ornithischia — the bird‑hipped, beaked herbivorous dinosaurs Ornithischia Ornithischia is a major clade of beaked, mainly herbivorous dinosaurs distinguished by a backward‑pointing pubis and diverse groups including stegosaurs, ankylosaurs, hadrosaurs an…

Ornithocheirus: a crested pterosaur genus Ornithocheirus Ornithocheirus is a genus of crested pterosaur known from fragmentary Cretaceous fossils; notable for long jaws with conical teeth, fish-eating habits, and a complex taxonomic hist…

Ornitholestes: a small Late Jurassic coelurosaur Ornitholestes Ornitholestes was a small, agile carnivorous dinosaur from the Late Jurassic. Known from a single partial skeleton, it helped shape ideas about early coelurosaur anatomy, behavior…

Ornithomimidae: the ostrich-like theropods Ornithomimidae Ornithomimidae were fast, mostly toothless theropod dinosaurs of the Late Cretaceous in Laurasia, known for long legs, probable feathers, and evidence suggesting herbivorous or omn…

Ornithomimus Ornithomimus is a genus of lightly built, fast-running theropod dinosaurs from Late Cretaceous North America, known for its toothless beak, long legs, and evidence of feathers.

Ornithopod dinosaurs: bird-hipped herbivores and their evolution Ornithopod Ornithopods (Ornithopoda) were a diverse group of herbivorous ornithischian dinosaurs, from small bipedal grazers to large, duck-billed hadrosaurs with complex chewing adaptations…

Ornithurae Ornithurae: the clade that unites living birds with their short‑tailed relatives, defined by a plough‑shaped pygostyle; overview of anatomy, fossil record, and evolutionary importa…

Orthoptera: grasshoppers, crickets and katydids — biology and importance Orthoptera Orthoptera are insects including grasshoppers, crickets, katydids and locusts. This article covers their anatomy, life cycle, sound production, ecology, classification and interact…

Oryx: antelopes adapted to deserts and dry grasslands Oryx Oryx are large, long‑horned antelopes native to arid regions of Africa and the Arabian Peninsula. This article explains their appearance, adaptations, behavior, species, and conser…

Oscar (Astronotus ocellatus) — popular South American cichlid Oscar (fish) Astronotus ocellatus, the oscar, is a large, intelligent South American cichlid kept in aquaria. Known for distinctive eye-spots, varied color morphs and strong territorial behavio…

Osornophryne — Andean plump toads Osornophryne Osornophryne is a small genus of true toads native to high-elevation forests and páramo in Colombia and Ecuador, notable for their compact bodies, high‑altitude habits and conserva…

Osprey (Pandion haliaetus): the fish-eating raptor Osprey A widespread bird of prey specialized for catching fish. Describes appearance, hunting adaptations, breeding, distribution, migration and conservation.

Ostafrikasaurus: Late Jurassic theropod known from a single tooth Ostafrikasaurus Ostafrikasaurus is a genus named from a large fossil tooth found in southeastern Tanzania. Its shape suggests affinities with early spinosaurids, but the classification remains ten…

Ostracod (seed shrimp): biology, diversity, ecology, and fossil importance Ostracod Ostracods are small bivalved crustaceans (seed shrimps) found in marine, freshwater and some terrestrial habitats. They have a rich fossil record and varied ecologies; taxonomy and…

Ostracoderms: Armoured Jawless Fishes of the Early Paleozoic Ostracoderm Ostracoderms were extinct, armored jawless vertebrates that lived from the Silurian to the Devonian. Their head shields and scales provide key evidence on the origin of bone, gill…

Ostreidae (true oysters): biology, uses, and distinctions Ostreidae Ostreidae, the true oysters, are a family of sessile bivalves known for irregular shells, a central adductor muscle scar, reef-building habits, and importance in cuisine and aquacu…

Oswego bass (regional common name for certain North American sunfish) Oswego bass Oswego bass is a regional common name applied to two different sunfish species in the Centrarchidae family. The name is ambiguous; identification depends on morphology, local usage…

Otter — aquatic mustelids: overview, behavior, habitat and conservation Otter Otters are semi-aquatic mammals in the Mustelidae family. Adapted for life in and near water, they vary from river otters to sea otters and play important ecological roles while fa…

Ouranosaurus: the sail-backed iguanodontid of Early Cretaceous Africa Ouranosaurus Ouranosaurus was a large, sail-backed herbivorous iguanodontid from the Lower Cretaceous of North Africa, known from nearly complete skeletons discovered in Niger and named by Phil…

Oviparous animals: egg-laying reproduction and its diversity Oviparous animals Oviparous animals reproduce by laying eggs. This article explains egg structure, fertilization modes, examples across animal groups, evolutionary significance, and differences from…

Oviraptor — toothless, crested theropod of the Late Cretaceous Oviraptor Oviraptor, a toothless, likely feathered theropod from the Late Cretaceous of Mongolia, known from a nest-associated specimen. Notable for parental-care evidence, crest uncertainty…

Oviraptorosaurs: the beaked, feathered maniraptorans of the Cretaceous Oviraptorosaur Oviraptorosaurs were a diverse group of feathered, beaked maniraptoran dinosaurs of the Cretaceous, notable for their birdlike anatomy, varied diets, and important fossil record in…

Ovis — genus of sheep (wild and domestic) Ovis Ovis is the sheep genus in the Caprinae subfamily, comprising wild and domestic sheep species known for horns, wool, grazing habits, and adaptations to mountainous and steppe habit…

Owl (Strigiformes): biology, behavior and global distribution Owl Owls are nocturnal or crepuscular birds of prey in the order Strigiformes. This article summarizes their anatomy, hunting adaptations, diversity, habitat, and relationship with peo…

Oxalaia — a spinosaurid theropod from the Cretaceous of Brazil Oxalaia Oxalaia is a genus of large spinosaurid theropod known from fragmentary snout bones found in Brazil; it lived in coastal and river environments during the early Late Cretaceous and…

Oxpecker (Buphagidae): African birds that cling to large mammals Oxpecker Two species of African savanna birds that feed on ticks and other parasites from large mammals; overview of biology, behavior, taxonomy, and their complex relationship with hosts.

Oystercatcher: coastal shorebird with a specialized bill Oystercatcher Oystercatchers are distinctive shorebirds (genus Haematopus) with long, strong bills used to feed on bivalves and other invertebrates along coasts and mudflats worldwide.

Paa hazarensis (Hazara frog) Paa hazarensis Paa hazarensis is a true frog of the Ranidae family found in montane streams and wetlands of South Asia. It inhabits high-altitude rivers, marshes and shrubland and is sensitive to…

Paa sternosignata: a South-Central Asian river frog Paa sternosignata Paa sternosignata is a ranid frog of South-Central Asia found in freshwater rivers, swamps and marshes in Afghanistan, Pakistan and Kashmir; its full range and ecology need further…

Paa vicina — a montane frog of India and Pakistan Paa vicina Paa vicina is a montane frog in the family Ranidae found in parts of India and Pakistan. It occupies high-altitude streams and grasslands and faces pressure from habitat loss and w…

Pacas (Genus Cuniculus): Distribution, Diet, and Human Interactions Paca Overview of pacas (genus Cuniculus): their Central and South American range, herbivorous diet and feeding habits, and human interactions including hunting, management, and captive…

Pachycephalosauria — the thick‑skulled marginocephalians Pachycephalosauria Pachycephalosaurs were small to medium bipedal ornithischian dinosaurs with thickened skull roofs. Known for domed heads and possible head‑butting behavior, they lived mainly in th…

Pachycephalosaurus: the dome-headed Late Cretaceous ornithischian Pachycephalosaurus Pachycephalosaurus was a bipedal, dome-skulled herbivorous dinosaur from the latest Cretaceous of western North America, known mainly from skull material and noted for its thick cr…

Pachypleurosaur: small marine sauropterygians of the Triassic Pachypleurosaur Pachypleurosaurs were early marine sauropterygians of the Triassic with elongated bodies, paddle-like limbs, and peg-like teeth; their fossils illuminate the origin of later plesio…

Pachyrhinosaurus — thick-nosed ceratopsian of the Late Cretaceous Pachyrhinosaurus Pachyrhinosaurus was a large, herbivorous ceratopsian known for its thick nasal boss, short frill and ornate frill ornamentation; fossils come from Late Cretaceous North America an…

Pacific giant salamander Large salamanders of the genus Dicamptodon native to the Pacific Northwest of North America; notable for size, aquatic larvae, occasional paedomorphosis, and loud vocalizations.

Pacific tree frog (Pseudacris regilla): description, habits and distribution Pacific tree frog Concise account of the Pacific tree frog (Pseudacris regilla): identification, behavior, habitat, diet, reproduction, range on the North American Pacific Coast, vocalizations, and…

Pack (canine social group) Pack (canine) A pack is a cooperative social group formed by certain canids for hunting, breeding and territory defence. Pack size, roles and behaviour vary by species and by ecological context.

Pack hunting: cooperative predation across animals Pack hunter Pack hunting (social predation) is cooperative hunting by conspecifics. This article explains strategies, examples across taxa, evolutionary reasons, ecological roles, and distinct…

Pack rat (Neotoma) — woodrat overview and natural history Pack rat Pack rats (genus Neotoma) are North American rodents noted for building middens and collecting objects; common in western deserts and highlands and important to ecology and paleont…

Packy — notable Asian elephant at the Oregon Zoo Packy (elephant) Packy (1962–2017) was a male Asian elephant born at the Oregon Zoo whose 1962 birth was the first in the Western Hemisphere in 44 years; he became an important figure in zoo breedi…

Paedophryne — tiny leaf‑litter frogs of Papua New Guinea Paedophryne Paedophryne is a genus of microhylid frogs from Papua New Guinea noted for extreme miniature size, leaf‑litter habits, and interest to studies of vertebrate miniaturization and tro…

Pakicetus — an early Eocene proto‑whale and transitional cetacean Pakicetus Pakicetus is a genus of early Eocene protocetid cetacean from what is now Pakistan. Its anatomy shows a mix of terrestrial and aquatic traits and it is key to understanding whale o…

Pal (1940–1958): the original dog who played Lassie Pal Pal was the male rough collie who originated the role of Lassie in 1940s MGM films and in early television; trained by Rudd Weatherwax, his line of collies continued the role for d…

Palaeodictyoptera: extinct order of large Paleozoic winged insects Palaeodictyoptera Palaeodictyoptera were an early order of winged insects common in Carboniferous coal forests, notable for beak-like mouthparts, prothoracic winglets and some very large wingspans;…

Palaeognathae: paleognaths, the ratites and tinamous Palaeognathae Palaeognathae is one of two main clades of living birds, defined by an ancient palatal structure. It includes flightless ratites and the volant tinamous; molecular evidence shows r…

Palaeothere — extinct perissodactyl browsers of the Eocene–Oligocene Palaeothere Palaeotheres were small to medium herbivorous perissodactyls that lived in Eurasian forests during the Eocene and Oligocene. They are important for understanding early ungulate evo…

Paleothyris: an early Pennsylvanian anapsid reptile Paleothyris Paleothyris was a small anapsid reptile from the Pennsylvanian of Nova Scotia. Around a foot long and likely insectivorous and nocturnal, it illuminates early amniote anatomy and e…