Birds
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This article is divided into 3 sections |
1. Evolution
Birds are now considered to be the direct descendants of extinct dinosaurs; indeed both birds and dinosaurs are grouped in the same clade dinosauria. The first extinct bird species discovered, showing some reptilian features was the archaeopteryx (archaeopteryx lithographica), which was found in 1861 in a Late Jurassic Lithographic Limestone near Soinhofen, Germany. Darwin's "Origin of Species" was published two years later.
Archaeopteryx was about the size of a crow with short, broad wings and a long tail. While its feathers were similar to those of living birds, it had jaws lined with sharp teeth, three fingers on its wings ending in curving claws, and a long bony tail.
Later, in the 1870s, other toothed birds, in particular the Ichthyornis and the Hesperornithoformes, were found in Kansas. Full details of these discoveries are given at http://www.oceansofkansas.com. The three pages Field Guide, Part 4, Hesperornis and Ichthyornis at that site are the most relevant.
In the late 1990s, several species of feathered dinosaur were found in China. See Science Daily (30 Jun 1998) for a report and New Scientist - Gallery - Feathered Dinosaurs for some images.
The oldest known bird with a beak was reported in 1995 by L. Hou, Z. Zhou and others. It was named Confuciusornis sanctis after the Chinese moral philosopher Confucius (551 - 479 B.C.). Confuciusornis is a crow-sized primitive bird from the Early Cretaceous of China. See Scientific-web.com - Confuciusornis for further information.
Despite the nonsense still published by creationists, there is now no doubt that birds are modern dinosaurs.
2. Classification
Aves or Birds are traditionally divided into 23 fairly large groups called Orders such as
and several more. These orders are of varying sizes. Over half the birds known are in just one order, the Passeriformes or Passerines.
After this we have Families; within each family are a number of genera and within each genus are a number of species.
For instance, the Ostrich is a member of the following sets:
See Earthlife Web - An Introduction to the Classification of Birds.
Also Bird Classification - Birding India.
The classification of birds is a contentious issue and keeps changing. Sibley & Ahlquist's Phylogeny and Classification of Birds (1990) is the work normally consulted by ornithologists at present.
The Cladistics of Aves at Tolweb uses several intermediate groups besides order and family. The basic cladistic scheme for all birds is as shown in Table 1.
Table 1: All birds
| A v e s | Archaeopteryx | |
| Confuciusornithidae | ||
| Enantiornithes | ||
| Euornithes | Patagopteryx | |
| Hesperornithoformes | ||
| Ichthyornithoformes | ||
| NEORNITHES | ||
The NEORNITHES or modern birds are further grouped as in Table 2.
Table 2: Modern birds
| | | - | --- Palaeoagnathae | ||
| NEORNITHES --- | | | |||
| | | Neognathae | | | --- Galloanserae | |
| | | | | |||
| | | --- Neoaves | |||
2.1 Palaeognathae
These consist of a number of groups of flightless birds, along with the tinamous. They were grouped together by Thomas Huxley (1867) on the basis of their distinctive palate morphology, from which they receive their name ("old jaw"). They are probably the oldest surviving lineage of Neornithes, and are thought to have originated in the Cretaceous.
Source:http://gigadino.pagesperso-orange.fr/Ratite.html
Palaeognathae is traditionally divided into two groups, the flightless ratites (defined by the absence of a keel on the sternum) and the tinamous which do fly. The morphological and behavioural similarities of the ratites suggest common ancestry. but recent analyses indicate that ratites are polyphyletic. The distribution of ratites is remarkable; ostriches live in Africa, rheas in South America, emus and cassowaries in Australasia, kiwis and moas (now extinct) in New Zealand, and elephant birds (also now extinct) in Madagascar.
Ostriches are the only palaeognaths which live in the old world; tinamous were unknown until the discovery of America. Carl Linnaeus published his work Systeme Naturae, which established binomial nomenclature, in several editions between 1735 and 1767. The British navigator and explorer, James Cook, reached New Zealand in 1769 and surveyed the eastern coast of Australia in 1770, after which several more species of flightless birds were discovered.
Ratite monophyly was debated through much of the last century and the hypothesis is supported by many recent studies. This would suggest a single loss of flight in their common ancestor. However, ratites would be unable to achieve their present distribution on southern land masses if their common ancestor was flightless. Although the proposed phyletic branching patterns for ratites do not correspond perfectly to the order of separation of landmasses during the breakup of Gondwanaland, continental drift is a convenient mechanistic explanation for ratite distribution.
Details of this cladistic analysis are given in the PNAS paper "phylogenomic evidence for multiple losses of flight in ratite birds" by Harshman et al. [www.pnas.org/content/105/36/13462].
2.1.1. Ostriches. The ostrich (Struthio camelus) is the tallest and heaviest of all living bird species. There are five subspecies:
Ostriches weigh from 198 to 286 pounds and are between 6 and 9 feet tall. Their eggs are the largest of all bird eggs, which are up to 4.5 × 7 inches across and weigh 3 pounds. Their geographic distribution is given at www.oiseaux.net|Common Ostrich Range.
Ostrich feathers are loose, soft and smooth, and are quite different from the stiff airfoil feathers of flying birds. Adult male feathers are mostly black, with some white on the wings and tail, while females and young males are greyish brown, with a bit of white. The small wings are used by males in mating displays, and can also provide shadow to chicks. There are claws on two of the wings' fingers (see flickr image; more information in the next section). The bird stands on two toes, with the bigger one resembling a hoof. The eyes of the ostrich, with their thick black eyelashes, are the biggest eyes of all living land animals.
Ostriches can sprint in short bursts up to 43 miles per hour, and can maintain a steady speed of 31 miles per hour. When an ostrich senses danger, it flops to the ground with its head and neck flat. From a distance, it looks like the ostrich has buried its head in the sand.
More information on ostrich life and behaviour is available at the page Ostrich - Laurie's Lil' Tyke Childcare. A more concise account is given at animals.about.com - ostrich.
2.1.2 Bird wing claws. Ostriches have three claws on each wing. Emus and cassowaries also have wing claws. This, however, is not especially a ratite feature. The Hoatzin has small claws on its first and second wing digits when it is young (it uses them to climb trees). The Turaco also has wing claws when young. The last two belong to isolated subgroups of the class Neoaves.
The following information is given at the Oxford Journals paper "The Integumentary Morphology of Modern Birds - An Overview" by Peter R. Stattenheim (2000):
Avian claws, like those of reptiles, are coverings of heavily cornified integument over the bone of a terminal phalanx. All birds have toe claws and many birds have wing claws as well. a toe claw is composed of a dorsal plate that curves downward on the tip and a ventral plate that fills the space between the sides underneath. The dorsal plate is the harder,containing heavy deposits of beta-keratin plus calcium salts.
Toe claws vary in length, curvature, and pointedness in relation to their usage and the substrate where a bird lives. They are flattened in grebes, contributing to the foot paddle. The claws have pectinate (comb) edges, used for grooming the feathers in nightjars, herons, frigatebirds,and pratincoles.
Wing claws are simple sheaths, not composed of plates. They were present on all three wing digits in the Jurassic bird Archaeopteryx lithographica and several Cretaceous dinosaurs. since Hoatzin (Opsthicomus hoazin) chicks possess functional wing claws on two digits, this species was formerly regarded as primitive. Young Hoatzins use these small hooks for climbing around branches and shed them at 70 - 100 days of age (Thomas, B.T. 1996. Family Opisthocomidae (Hoatzin). In J. del Hoyo, A. Elliott, and J. Sargatal (eds.), Handbook of birds of the world, Vol. 3, pp. 24 - 32. Lynx Edicions, Barcelona). Adult loons, storks, screamers, galliformes, Secretary Birds (Sagittarius serpentarius),owls, finfoots, and charadrii formes have small, non-functional claws on the tip of the alular digit. Adult cassowaries, however, have a large, pointed claw on the tip of the main digit, which they use as a formidable weapon.
2.1.3. Tinamous.About 47 species found in Central and South America, they represent one of the oldest stocks of birds found on the South American continent. Their fossil remains in Argentina date back to the the Late Miocene Epoch (about 10 million years ago). The structure of the bony palate quite clearly links the tinamous and rheas.
Tinamous are quail-like in appearance and not very good fliers. They take to flight only when alarmed.
The order Tinamoformes to which tinamous belong has only one family (Tinamidae) and two sub-families (Tinaminae, Rhynchotinae). The Tinaminae is represented by 3 genera (Crypturellus, Northocercus, Tinamus) with 29 species and the Rhyncholinae by 6 genera (Eudomia, Northoprocta, Northura, Rhynchotus, Taoniscus, Tinamotis) with 18 species. A species list is given at Tinamous | The Internet Bird Collection. Flipping through the previous pages of this site, you will find lists of all palaeognath orders. An account of tinamou behaviour is given in the on-line Encyclopedia Britannica CD page Birds: MAJOR BIRD ORDERS: Tinamiformes (tinamous). On the matter of vocalisation, it states:
The voices of tinamous are among the strongest and most pleasant of any in the neotropics. They consist of loud, stereotyped, but melodious whistles, varying from the long and astonishingly songlike sequence of the brown tinamou (Crypturellus obsoletus) -- astonishing because most relatives of the tinamous do not produce elaborate vocalisations -- to the monosyllabic call of the cinareous tinamou (C. cinareus). The calls of the male and female are similar but discernably different to the human ear. The female solitary tinamou (Tinamus solitarius) has a special call given during the time before egg laying, and another call is uttered by both sexes of this species after perching at dusk.
Tinamou cladistics from paper by Bertelli and Porzencanski (2004).
3. Neoagnathae
As mentioned above, the Neoagnathae are further split up into two clades, Galloansarae and Neoaves. Neoaves is discussed further in the continuation page Birds (2).
Galloanserae are further subdivided into
Of these, Poultry are of particular importance to our economy. Pigeons, ducks and geese were bred in China more than 3,000 years ago. Chickens, developed from the Asian jungle fowl, were domesticated probably around the same time. although eggs were artificially incubated in ancient China and Egypt, this method was not used commercially until the 1870s.
The last poultry bird to be domesticated was the Turkey. Wild turkeys (Meleagris gallopavo) live in woods in parts of North America. Unlike their domestic descendants, which weigh twice as much as them, they are unable to fly.
The classification of Neoaves may be found at TOLWEB. "Land Birds" and "Water Birds" are informal names for two large clades within Neoaves, each encompassing several traditional orders. "Land Birds" include the Passeriformes, or Perching Birds, which is the best known of all bird clades.
Completed 06 Sep 2013
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