Bird Classification and Evolution
Birds belong to Vertebrates, the group of animals with a vertebral column. More precisely, Birds belong to the Tetrapods, the four-limbed vertebrates, which also include amphibians, mammals and all reptiles.
Archaeopteryx, the oldest bird yet discovered, is known from several fossils recovered from fine slate deposits in Germany. This magpie-size animal lived in a tropical environment about 150 million years ago. Archaeopteryx had flight feathers and a fused furcula (ie, wishbone) resembling those of modern birds; these features are, so far, unique in Jurassic animals. Its solid bones and lack of a keel on the breastbone limited its powers of flight. This made it more a glider than a powered flyer and it may have been capable only of gliding from perch to perch. Archaeopteryx had many features that are also present in theropod Dinosaurs, and many scientists now believe that birds have evolved from feathered dinosaurs.
Most fossil birds from the Cretaceous period (142-65 million years ago) belong to extinct groups, such as the Enantiornithines or "opposite birds," characterized by shoulder girdle articulations and leg bone features that are opposite to those of modern birds. The birds that survived the catastrophic extinctions at the end of the Cretaceous diversified into species modern in appearance and often can be referred to modern groups of birds.
Modern Linnaean classification groups species according to how closely related they are to one another. Species belonging to the same genus have a more recent common ancestor than those placed in different genera. The same is true for grouping genera into families and families into orders. Studies comparing the DNA of bird species have shed new light on the relationships of birds (and is continuing to do so), but many of the groupings originally based on morphological grounds have nevertheless proved valid.
Although birds are perhaps better known than of any other animal group, new species are still discovered almost yearly. Nearly 10 000 species of recently identified birds are known and they are grouped in more than 200 families, more than 2200 genera and 29 orders. About two-thirds of known species (close to 6000 species) belong to the order Passeriformes (perching birds). The remaining 4000 species or so belong to 28 orders divided in nearly 100 families and about 1000 genera. The following summary of how birds are currently classified in different orders, families and genera, gives an indication of the diversity of bird species.
Tinamiformes (one family, 9 genera, 47 species; none in Canada). Tinamous. Medium-size ground-dwelling birds; New World distribution.
Struthioniformes (5 families, 6 genera, 14 species; none in Canada). Ostriches, rheas, cassowaries, emus, kiwis. Large birds, except kiwis; flightless and cursorial (ie, running); found mostly in the Southern Hemisphere.
Galliformes (5 families, 80 genera, 290 species; 16 breeding species in Canada). Megapodes, curassows, chachalacas, guineafowl, quails, turkeys, grouse, ptarmigan, pheasants, peafowl, partridge. Small to very large chickenlike birds; occur almost worldwide.
Anseriformes (3 families, 52 genera, 162 species; 39 breeding species in Canada). Screamers, geese, swans, ducks, teals, mergansers. Medium-size to very large swimming birds with 3 webbed toes and lamellate bill, except screamers (restricted to South America), which have unwebbed feet, chickenlike bills and wading habits; worldwide distribution. The Labrador duck, formerly found in Canada, is extinct (see also Endangered Animals).
Sphenisciformes (one family, 6 genera, 17 species; none in Canada). Penguins. Medium-size to large diving birds with flipperlike wings; found in the Southern Hemisphere.
Gaviiformes (one family, one genus, 5 species; 4 breeding species in Canada). Loons. Large diving birds with 3 webbed toes and straight, pointed bill; found in the Northern Hemisphere.
Procellariiformes (4 families, 26 genera, 112 species; 4 breeding species in Canada). Albatrosses, fulmars, shearwaters, storm-petrels, diving-petrels. Very small to very large oceanic birds with 3 webbed toes and tubular nostrils; nest on land; found on all oceans.
Podicipediformes (one family, 6 genera, 22 species; 6 breeding species in Canada). Grebes. Small to large diving birds with lobed toes and straight, pointed bills; worldwide distribution.
Phoenicopteriformes (one family, 3 genera, 5 species; none in Canada). Flamingoes. Large wading birds with long legs and necks; bill thick with lamellae (ie, tiny, comblike structures) and bent sharply downward at midpoint; toes webbed; colonial nesters, mainly in tropical and sub-tropical areas.
Ciconiiformes (3 families, 39 genera, 116 species; 10 breeding species in Canada). Bitterns, herons, egrets, storks, ibises, spoonbills. Small to very large wading birds with long legs and necks; bill varies from long and spearlike to broad, flat and shovellike or downward curved; worldwide distribution.
Pelecaniformes (8 families, 10 genera, 65 species; 6 breeding species in Canada). Tropicbirds, frigatebirds, pelicans, boobies, gannets, cormorants, anhingas. Medium-sized to large aquatic birds, pointed or hooked bills; primarily colonial nesters; worldwide distribution.
Falconiformes (3 families, 83 genera, 304 species; 19 breeding species in Canada). Falcons, vultures, secretary birds, kites, hawks, eagles, osprey. Very small to very large diurnal birds of prey; legs short to very long; wing shape highly variable from very pointed to broad and rounded; hunters or carrion feeders; worldwide distribution.
Gruiformes (11 families, 61 genera, 212 species; 8 breeding species in Canada). Bustards, mesites, seriemas, kagus, rails, gallinules, coots, sun-grebes, trumpeters, cranes, limpkins, buttonquails. Very small to very large birds; structure diverse, most have cursorial habits; worldwide distribution.
Charadriiformes (17 families, 88 genera, 367 species; 84 breeding species in Canada). Thick-knees, sheathbills, oystercatchers, crabplovers, avocets, plovers, painted-snipes, jacanas, sandpipers, phalaropes, pratincoles, gulls, terns, skimmers, jaegers, skuas, auks, sandgrouse. Small to large birds; many species with long legs, cursorial habits; some with webbed feet and aquatic or diving habits; structure and habits diverse; worldwide distribution. Great auk, which nested in Canada, is extinct.
Columbiformes (one family, 44 genera, 311 species; 4 breeding species in Canada). Dodos, pigeons, doves. Very small to very large birds; solitary to highly gregarious; arboreal or terrestrial; worldwide distribution. Dodo, native to the Mascarene Islands, and passenger pigeon, formerly very common in Canada, are extinct.
Psittaciformes (one family, 85 genera, 364 species; none in Canada). Cockatoos, lories, budgerigars, parakeets, parrots. Very small to large birds with brightly coloured plumage, strong hooked bill; 2 toes in front, 2 behind; mainly in tropical and sub-tropical areas. Carolina parakeet, formerly of North America (possibly southern Ontario), is extinct.
Opisthocomiformes (one family, one genus, one species; none in Canada). Hoatzin. Medium-size arboreal birds that feed on green leaves; young has claws on wings; South America.
Musophagiformes (one family, 6 genera, 23 species; none in Canada). Turacos and plantain eaters. Medium-size birds with long tails; chiefly arboreal; Africa.
Cuculiformes (one family, 35 genera, 138 species; 2 breeding species in Canada). Cuckoos. Small to large birds with long tails; 2 toes in front, 2 behind, or fourth reversible; many species have parasitic nesting habits; mostly arboreal, a few terrestrial species; worldwide distribution.
Strigiformes (2 families, 29 genera, 195 species; 16 breeding species in Canada). Owls. Small to large birds; primarily nocturnal and arboreal; raptorial habits, noiseless flight; large eyes directed forward; worldwide distribution.
Caprimulgiformes (5 families, 22 genera, 118 species; 4 breeding species in Canada). Oilbirds, frogmouths, potoos, goatsuckers, nightjars, nighthawks. Small- to medium-size birds; bill usually with wide mouth surrounded with bristles; small, weak feet; nocturnal or crepuscular insect or fruit eaters; worldwide distribution.
Apodiformes (3 families, 124 genera, 429 species; 9 breeding species in Canada). Swifts, hummingbirds. Small birds with weak feet. Swifts, distributed worldwide, have long, strong wings; hummingbirds, restricted to New World, have slender, pointed, long bills, and generally iridescent plumage.
Coliiformes (one family, 2 genera, 6 species; none in Canada). Mousebirds or colies. Small birds with long tails; gregarious and arboreal; Africa.
Trogoniformes (one family, 6 genera, 39 species; none in Canada). Trogons, quetzals. Colourful, small- to medium-size birds with long tails; solitary and arboreal; tropical areas.
Coraciiformes (7 families, 34 genera, 149 species; one breeding species in Canada). Rollers, kingfishers, todies, motmots, bee-eaters. Small to large birds; strong bill; some toes fused at base; worldwide distribution.
Bucerotiformes (4 families, 17 genera, 60 species; none in Canada). Hornbills, hoopoes. Small- to large-size birds, with long bill and some toes fused at base; Old World distribution.
Galbuliformes (2 families, 15 genera, 61 species; none in Canada). Jacamars, puffbirds. Small- to medium-size tropical birds; strong bill; some toes fused at base; New World distribution.
Piciformes (3 families, 53 genera, 347 species; 14 breeding species in Canada). Barbets, toucans, honeyguides, wrynecks, piculets, woodpeckers. Small to large birds; most species solitary and arboreal; bill highly variable, from short, straight and pointed to very large; 2 toes in front, 2 behind, some species have only 3 toes; worldwide distribution, except for Australian region.
Passeriformes (97 families, more than 1200 genera, about 5800 species; 195 breeding species in Canada). Perching birds: flycatchers, shrikes, vireos, jays, magpies, crows, ravens, waxwings, chickadees, swallows, larks, kinglets, wrens, gnatcatchers, nuthatches, creepers, mockingbirds, thrashers, starlings, thrushes, robins, dippers, pipits, finches, warblers, meadowlarks, blackbirds, grackles, orioles, buntings, tanagers, cardinals, grosbeaks, sparrows. Comprises more species than all other orders together; highly diversified; adapted to perching, 3 toes in front, one behind; small to medium size; contains all songbirds; worldwide distribution.