Some Amazing Facts About Animal

Some Amazing Facts About Animal

Cows Have Best Friends
You might think that friendship is a completely unique human experience, but actually that's not true at all. Not only do animals have friends, but cows have been shown in studies to have 'best friends' – even showing signs of distress when they get separated from them.
 Many Animals Can Use Tools
Another trait that seems very human is the ability to think creatively and engineer solutions by using raw materials. Again though, this is something that animals can do too – not only can primates use sticks to fish ants out of trees and to club snakes (chimpanzees even make spears!), but many other animals have also found useful uses for the things in their environment. Some birds for instance use traffic in order to crack open nuts, while elephants have been known to short out electric fences by dropping branches on them. Dolphins have been spotted using sponges to stir up sand on the ocean floor when looking for prey, Gorillas have used branches as walking sticks and to test water depth, octopuses use coconut shells to make armour and deguses (rodents similar to chinchillas) can use little rakes to bring food closer to their cage. Some chimps even have toys – treating sticks like 'babies' in the same way children used dolls. And what do you call a nest if not a bed made out of sticks? Don't feel so special now do you?
Chimpanzees Believe in God
Okay not quite, but chimpanzees have been seen displaying behaviours that are thought to be 'quasi religious'. When faced with fires, waterfalls or storms – chimpanzees (which are our closest relatives) have been seen to react with rituals and even to perform a particular 'rain dance'. This could be the early signs of the same kind of 'worship' that ultimately lead to the kinds of religions we have today. Who knows? Perhaps they believe the rain is caused by the big chimp in the sky?
Chimps Can Light Fire
Not impressed enough by chimpanzees? How about this – when in captivity they can actually be taught to control fire using matches and other similar tools. And we know what that discovery ultimately lead to for humans (tip: you wouldn't be reading this if our early ancestors had never discovered fire…).
Alex the Amazing Parrots
It's not just chimps that challenge our view of animal psychology – also impressive are parrots and one parrot in particular – named Alex – demonstrated this to an amazing extent.
Alex was not only able to mimic words, but also use them in the correct context: identifying foods, shapes and even materials. More impressive still, he could use this ability to make requests for things he wanted. That's not just mimicking – that's talking! Now imagine if you gave a chimpanzee a greater vocal range: what could they accomplish then?
Rats Laugh
Laughing is a strange enough phenomenon as it is, but it's even more unusual to think that animals can laugh in the same sense as we can. Actually that's true, and rats will laugh when tickled under their bellies…
Some Animals Can Commit Suicide
Giggling rats is a cute idea, but this one is a little more grim: both elephants and dolphins are known to be capable of committing suicide. When in harsh conditions an elephant will step on its own trunk in order to suffocate itself. Think about the implications for the intelligence of those animals: it means that they not only have a sense of 'future' (enough to know that their situation isn't likely to change), but also a grasp of their own anatomy and their mortality…
Tarra & Bella
The fact that elephants understand death isn't something that's new to us: and it's a well-known fact that elephants not only keep graveyards but also mourn their dead. A tale that might still impress you however is that of Tarra and Bella – an elephant and a dog who became best friends and were inseparable for a long time. When Tarra the dog eventually died, Bella found the body and carried it back home to her sanctuary. Not only did Bella spend time mourning – once again showing an understanding for life and death.
Dolphins Have Names
Dolphins are another species that are often focussed on for their smarts. A recent finding that exemplifies this is that dolphins actually have names for one another (which form when other dolphins mimic the sounds they make) – and recognise their own title when it is called by other dolphins.
Whales Have Pop Music
When mating, whales will make a certain kind of 'tune' that sounds like music. Now that on its own is nice, but not particularly indicative of intelligence. What is impressive though, is that these tunes will spread throughout whale populations and come in and out of fashion – a 'cultural' exchange much like our own. I wonder if they have an equivalent of Gangnam Style?
Male Pups Let Females Win
When play fighting, male puppies will sometimes let female puppies win on purpose in order to keep them happy. Again, this suggests that they not only understand the nature of the game they're playing, but are also able to empathise with the female puppies and predict how they are going to feel. This is something that some humans still apparently struggle with…
Monkeys Like Justice
And speaking of fairness, monkeys notice when receiving different payments for the same work and get understandably upset when they get the short shrift. This suggests that monkeys not only grasp fairness and equality, but also that they experience emotions like jealousy.
Pigs Can Play Computer Games
In one study, pigs were taught to play computer games in order to win treats. They can play basic games like Pong and Breakout (though 'Call of Duty' is a little above them) and even more impressive is the fact that you can now play with them using an iPad and a copy of 'Pig Chase'. Technically that's also an example of a pig using an iPhone and the internet.
For all you know, I'm a pig…

 

White-bellied heron

White-bellied heron

Taxonomy and systematics

This heron was first noted as the "great Indian heron" in JE Gray's Zoological Miscellany of 1844 based on Brian Houghton Hodgson from Nepal. Allan Octavian Hume noted its distinctiveness and pointed out the differences between it and Ardea sumatrana. The alternate name of Ardea imperialis was suggested by Stuart Baker, since Hodgson's name was a nomen nudum and this was used in Peters' check-list. This was used until 1963, when Biswamoy Biswas commented on Sidney Dillon Ripley's synoptic list and noted that Ardea insignis Hume should be used, since its citation as a synonym of Ardea nobilis Blyth and Ardea sumatrana Raffles was based on misidentification.

  

Description

This large heron is plain dark grey above with a long neck. The crown is dark and there are no black stripes on the neck as in the grey heron. In breeding plumage, it has a greyish-white nape plume and elongated grey breast feathers with white centers. The bill is black, greenish near the base and tip and the face is greenish grey. The bill is large and solid, with the culmen measuring 15.2–17.6 cm (6.0–6.9 in). The chin and central portion of the underside are whitish in color (per the common name), contrasting strongly against the dark grey color on the back. The legs are blackish with scale-like texture on the tarsus which measures 17.1 to 21.6 cm (6.7 to 8.5 in). In flight, it has a uniform dark grey upperwing and white underwing-coverts contrasting with dark grey flight feathers. The rump appears paler grey. At 127 cm (50 in) in height, it is the second largest heron on earth, after the Goliath heron. Included in the length, the mid-sized tail measures 19.9 to 21.6 cm (7.8 to 8.5 in). The wing chord measures 54.6 to 57.2 cm (21.5 to 22.5 in), with an estimated wingspan of 2 m (6.6 ft) or more. One estimate of body mass was relatively low at 2–2.6 kg (4.4–5.7 lb), however a deceased juvenile of the species reportedly weighed much more at 5.6 kg (12 lb). Another dead juvenile heron stood 1.58 m (5.2 ft) tall and weighed 8.51 kg (18.8 lb). These extremely high weights require verification, since they indicate this species can exceed even the typically larger Goliath heron in mass. On the ground it walks slowly, moving its neck slowly while looking from side to side. The Goliath species, beyond the average size difference, is distinguished by its chestnut neck while the slightly smaller great-billed heron is solid grey necked with the underside of the wings all grey. The usual call given when disturbed is a deep croak.

Habitat

The white-bellied heron is found in the wetlands of tropical and subtropical forests in the foothills of the eastern Himalayas of India and Myanmar. It also occurs in Bhutan's sub-tropical areas and was once found in Nepal. The major threats the heron faces are poaching (both the bird itself and its eggs) and habitat destruction (cutting of nesting trees and the disappearance of wetlands).
In Bhutan, white-bellied herons are found along the Punatsang Chu river especially in Pho-chhu river banks in Toewang Gewog, along Kami Chhu river) and in Lower Kheng (Berti). It can also be found in Madgechhu (Trongsa). A recently discovered nesting site in the Namdapha national park and Tiger Reserve in Arunachal Pradesh, India, is the first such breeding site outside of Bhutan.

 

 

 

Booted eagle

Booted eagle

 "Aquila minuta" redirects here. If based on Brehm (1831), it refers to this bird. The fossil bird described under the same name by Milne-Edwards (1871) is preliminarily known as "Hieraaetus" edwardsi but might belong in Aquila.

The booted eagle (Hieraaetus pennatus, also classified as Aquila pennata) is a medium-sized bird of prey. It is about 46 cm (18 in) in length and has a wingspan of 120 cm (47 in). Like all eagles, it belongs to the family Accipitridae. 

Description

 The booted is a small eagle, comparable to the common buzzard in size though more eagle-like in shape. Males grow to about 510–770 g (1.12–1.70 lb) in weight, with females about 950–1,000 g (2.09–2.20 lb). There are two relatively distinct plumage forms. Pale birds are mainly light grey with a darker head and flight feathers. The other form has mid-brown plumage with dark grey flight feathers.

Breeding and habitat

It breeds in southern Europe, North Africa and across Asia. It is migratory, wintering in Sub-Saharan Africa and South Asia. This eagle lays 1–2 eggs in a tree or crag nest.

Taxonomy

Based on recent genetic research^{[citation needed]} some authors reclassified this species to the genus Aquila, along with some^{[citation needed]} or all other Hieraaetus species. As it is the type species of Hieraaetus, should any of the hawk-eagles have been retained in a distinct genus then a new name for that group would have been necessary.

However, most reference lists currently use H. pennata.

Along with the little eagle, this bird is one of the closest living relatives of the extinct Haast's eagle of New Zealand.

Great white pelican

Description

The great white pelican is a huge bird, with only the Dalmatian pelican averaging larger amongst the pelicans. The wingspan can range from 226 to 360 cm (7.41 to 11.81 ft), with the latter measurement the largest recorded among extant flying animals outside of the great albatrosses. The total length of the great white pelican can range from 140 to 180 cm (55 to 71 in), with the enormous bill comprising 28.9 to 47.1 cm (11.4 to 18.5 in) of that length. Adult males, weigh from 9 to 15 kg (20 to 33 lb), though large races from the Palaearctic are usually around 11 kg (24 lb) with few exceeding 13 kg (29 lb). Females are considerably less bulky and heavy, weighing from 5.4 to 9 kg (12 to 20 lb). Among standard measurements, the wing chord length is 60 to 73 cm (24 to 29 in), the tail is 16 to 21 cm (6.3 to 8.3 in) and the tarsus is 13 to 14.9 cm (5.1 to 5.9 in). The standard measurements from differing areas indicate that pelicans of the species from the Western Palaearctic are somewhat larger in size than ones that reside in Asia and in Africa.
Immature great white pelicans are grey and have dark flight feathers. In flight, it is an elegant soaring bird, with the head held close to and aligned with the body by a downward bend in the neck. In breeding condition the male has pinkish skin on its face and the female has orangey skin. It differs from the Dalmatian pelican by its pure white, rather than greyish-white, plumage, a bare pink facial patch around the eye and pinkish legs. Males are larger than females, and have a long beak that grows in a downwards arc, as opposed to the shorter, straighter beak of the female. The spot-billed pelican of Asia is slightly smaller than the great white, with clear brownish-grey plumage and a paler, duller-colored bill. Similarly, the pink-backed pelican is smaller with brownish-grey plumage, with a light pink to off-grey bill and a pinkish wash to the back.
The great white pelican is well adapted for aquatic life. The short strong legs and webbed feet propel it in water and aid the rather awkward takeoff from the water surface. Once aloft, the long-winged pelicans are powerful fliers, however, and often travel in spectacular V-formation groups.

Distribution and habitat

Great white pelicans are usually birds found in and around shallow, (seasonally or tropical) warm fresh water. Well scattered groups of breeding pelicans occur through Eurasia from the eastern Mediterranean to Vietnam. In Eurasia, fresh or brackish waters may be inhabited and the pelicans may be found in lakes, deltas, lagoons and marshes, usually with dense reed beds nearby for nesting purposes. Additionally, sedentary populations are found year-round in Africa, south of the Sahara Desert although these are patchy. In Africa, great white pelicans occur mainly around freshwater and alkaline lakes and may also be found in coastal, estuarine areas. Beyond reed beds, African pelicans have nested on inselbergs and flat inshore islands off of Banc d'Arguin National Park. Migratory populations are found from Eastern Europe to Kazakhstan during the breeding season. More than 50% of Eurasian great white pelicans breed in the Danube Delta in Romania. They like to stay also in the Lakes near Burgas, Bulgaria and in Srebarna Lake in Bulgaria. The pelicans arrive in the Danube in late March or early April and depart after breeding from September to late November. Wintering locations for European pelicans are not exactly known but wintering birds may occur in northeastern Africa through Iraq to north India, with a particularly large number of breeders from Asia wintering around Pakistan. These are birds that are found mostly in lowlands, though in East Africa and Nepal may be found living at elevations of up to 1,372 m (4,501 ft).

Feeding behavior

The diet of the great white pelican consists mainly of fish. The pelicans leave their roost to feed early in the mornings and may fly over 100 km (62 mi) in search of food, as has been observed in Chad and Mogode, Cameroon. Each pelican needs from 0.9 to 1.4 kg (2.0 to 3.1 lb) of fish every day. This corresponds to around 28,000,000 kg (62,000,000 lb) of fish consumed every year at the largest colony of great white pelicans, on Tanzania's Lake Rukwa, with almost 75,000 birds. Fish targeted are usually fairly large ones, in the 500–600 g (1.1–1.3 lb) weight range, and are taken based on regional abundance. Common carp are preferred in Europe, mullet are preferred in China and Aphanius dispar (a carp) are preferred in India. In Africa, often the commonest cichlids, including many species in the Haplochromis and Tilapia genera, seem to be preferred. The pelican's pouch serves simply as a scoop. As the pelican pushes its bill underwater, the lower bill bows out, creating a large pouch which fills with water and fish. As the bird lifts its head, the pouch contracts, forcing out the water but retaining the fish. A group of 6 to 8 great white pelicans will gather in a horseshoe formation in the water to feed together. They dip their bills in unison, creating a circle of open pouches, ready to trap every fish in the area. Most feeding is cooperative and done in groups, especially in shallow waters where fish schools can be corralled easily, though these pelicans may forage alone as well.
Pelicans are not restricted to fish, however, and are often opportunistic foragers. In some situations they eat chicks of other birds, such as the well documented case off the southwest coast of South Africa. Here, breeding Pelicans from the Dassen Island colony predate chicks weighing up to 2 kg (4.4 lb) from the Cape gannet colony on Malgas Island. Similarly, in Walvis Bay, Namibia the eggs and chicks of Cape cormorants are fed regularly to young pelicans. The local pelican population is so reliant on the cormorants, that when the cormorant species experienced a population decline, the numbers of pelicans appeared to decline as well. Great white pelicans also eat crustaceans, tadpoles and even turtles. They readily accept handouts from humans, and a number of unusual items have been recorded in their diet.
During periods of starvation, pelicans also eat seagulls and ducklings. The gulls are held under water and drowned before being eaten headfirst. A flock of captive great whites in St James' Park, London (see below) is well-known for occasionally eating local pigeons, despite being well-fed.Pelicans will also rob other birds of their prey.

Breeding

The breeding season commences in April or May in temperate zones, is essentially all year around in Africa and runs February through April in India. Large numbers of these pelicans breed together in colonies. The female can lay from 1 to 4 eggs in a clutch, with two being the average. Nest locations are variable. Some populations making stick nests in trees but a majority, including all those who breed in Africa, nest exclusively in scrapes on the ground lined with grass, sticks, feathers and other material. The young are cared for by both parents. The incubation stage lasts for 29 to 36 days. The chicks are naked when they hatch but quickly sprout blackish-brown down. The colony gathers in "pods" around 20 to 25 days after the eggs hatch. The young fledge at 65 to 75 days of age. Around 64% of young successful reach adulthood, with sexual maturity attained at 3 to 4 years of age. White pelicans are often protected from bird-eating raptors by virtue of their own great size, but eagles, especially sympatric Haliaeetus species, may predate their eggs, nestlings and fledgings. Occasionally, pelicans and their young are attacked at their colonies by mammalian carnivores from jackals to lions. As is common in pelicans, the close approach of a large predaceous or unknown mammal, including a human, at a colony will lead the pelican to abandon their nest in self-preservation. Additionally, crocodiles, especially Nile crocodiles in Africa, will readily kill and eat swimming pelicans.

 

 

 

 

Southern cassowary

Southern cassowary

 The southern cassowary (Casuarius casuarius) also known as double-wattled cassowary, Australian cassowary or two-wattled cassowary, is a large flightless black bird. It is a ratite and therefore related to emu, ostrich, and the Rhea and Kiwi genera. (See also dwarf cassowary and northern cassowary.)

Taxonomy

Presently, most authorities consider the southern cassowary monotypic, but several subspecies have been described. It has proven very difficult to confirm the validity of these due to individual variations, age-related variations, the relatively few available specimens (and the bright skin of the head and neck – the basis of which several subspecies have been described – fades in specimens), and that locals are known to have traded live cassowaries for hundreds, if not thousands of years, some of which are likely to have escaped/been deliberately introduced to regions away from their origin.
Cassowaries are closely related to the kiwis, both families diverging from a common ancestor approximately 40 million years ago.
The binomial name Casuarius casuarius is derived from its Malay name kesuari. The southern cassowary was first described by Carl Linnaeus in his 18th century work, Systema Naturae, as Struthio casuarius, from a specimen from Seram, in 1758. It is now the type species of the genus Casuarius.
The southern cassowary has been described under a large number of scientific names, all of which are now considered taxonomic synonyms for the species.

Description

The southern cassowary has stiff, bristly black plumage, a blue face and neck, red on the nape and two red wattles measuring around 17.8 cm (7.0 in) in length hanging down around its throat. A horn-like brown casque, measuring 13 to 16.9 cm (5.1 to 6.7 in) high, sits atop the head. The bill can range from 9.8 to 19 cm (3.9 to 7.5 in). The three-toed feet are thick and powerful, equipped with a lethal dagger-like claw up to 12 cm (4.7 in) on the inner toe. The plumage is sexually monomorphic, but the female is dominant and larger with a longer casque, larger bill and brighter-colored bare parts. The juveniles have brown longitudinal striped plumage. It is the largest member of the cassowary family and is the second heaviest bird on earth, at a maximum size estimated at 85 kg (187 lb) and 190 cm (75 in) tall. Normally this species ranges from 127 to 170 cm (50–67 in) in length. The height is normally 1.5 to 1.8 m (4.9–5.9 ft) and females average 58.5 kg (129 lb) and males averaging 29 to 34 kg (64–75 lb). Most adult birds will weigh between 17 and 70 kg (37 and 154 lb). It is technically the largest Asian bird (since the extinction of the Arabian ostrich, and previously the moa of New Zealand) and the largest Australian bird (though the emu may be slightly taller).

Behaviour

It forages on the forest floor for fallen fruit and is capable of safely digesting some fruits toxic to other animals. They also eat fungi, and some insects and small vertebrates. The southern cassowary is a solitary bird, which pairs only in breeding season, which takes place in late winter or spring. The male builds a nest on the ground; a mattress of herbaceous plant material 5 to 10 centimetres (2–4 in) thick and up to 100 centimetres (39 in) wide. This is thick enough to let moisture drain away from the eggs. The male also incubates the eggs and raises the chicks alone. A clutch of three or four eggs are laid measuring 138 by 95 millimetres (5.4 in × 3.7 in). They have a granulated surface and are initially bright pea-green in colour although they fade with age.
They make a booming call during mating season and hissing and rumblings otherwise. Chicks will make frequent high-pitches whistles to call the male.
The blade-like claws are capable of killing humans and dogs if the bird is provoked.

 

Little grebe

Little grebe

Description

The little grebe is a small water bird with a pointed bill. The adult is unmistakable in summer, predominantly dark above with its rich, rufous colour neck, cheeks and flanks, and bright yellow gape. The rufous is replaced by a dirty brownish grey in non-breeding and juvenile birds.
Juvenile birds have a yellow bill with a small black tip, and black and white streaks on the cheeks and sides of the neck as seen below. This yellow bill darkens as the juveniles age, eventually turning black in adulthood. In winter, its size, buff plumage, with a darker back and cap, and “powder puff” rear end enable easy identification of this species. The little grebe's breeding call, given singly or in duet, is a trilled repeated weet-weet-weet or wee-wee-wee which sounds like a horse whinnying.

Distribution

This bird breeds in small colonies in heavily vegetated areas of freshwater lakes across Europe, much of Asia down to New Guinea, and most of Africa. Most birds move to more open or coastal waters in winter, but it is only migratory in those parts of its range where the waters freeze. Outside of breeding season, it moves into more open water, occasionally even appearing on the coast in small bays.

Behaviour

The little grebe is an excellent swimmer and diver and pursues its fish and aquatic invertebrate prey underwater. It uses the vegetation skilfully as a hiding place.
Like all grebes, it nests at the water's edge, since its legs are set very far back and it cannot walk well. Usually four to seven eggs are laid. When the adult bird leaves the nest it usually takes care to cover the eggs with weeds. This makes it less likely to be detected by predators. The young leave the nest and can swim soon after hatching, and chicks are often carried on the backs of the swimming adults. In India, the species breeds during the rainy season.
It does not normally interbreed with the larger grebes in the Old World, but a bird in Cornwall mated with a vagrant North American pied-billed grebe, producing hybrid young.

 

 

Pheasants and partridges

Pheasants and partridges 

Snow partridge

 The snow partridge (Lerwa lerwa) is a gamebird in the pheasant family Phasianidae found widely distributed across the high-altitude Himalayan regions of India, Pakistan, Nepal and China. It is the only species within its genus. The species is found in alpine pastures and open hillside above the treeline but not in as bare rocky terrain as the Himalayan snowcock and is not as wary as that species. Males and females look similar in plumage but males have a spur on their tarsus

This species was first described by Brian Houghton Hodgson in 1833 and given the genus name Lerwa based on the Bhutia name for it in Nepal. Hodgson initially placed it in the genus Perdix calling it Perdix lerwa. A subspecies, L. l. major was described by Richard Meinertzhagen from Szechuan while L. l. callipygia from south Kansu was noted by Stegmann in 1938, but these are not usually recognized. The species has been retained in this monotypic genus due to various peculiarities including the tarsus feathering and the lack of clear sexual dimorphism in plumage. A species of bird louse, Chelopistes lervicola has been described as an ectoparasite of this species, and other species in this louse genus are known to parasitize the Cracidae, Meleagrididae and Odontophorinae of the New World.

 

Behaviour and ecology

The snow partridge is found is small groups, usually about 6 to 8 but up to 30 during the non-breeding season. When flushed, they usually fly up before scattering away with noisy wing beats. The flight is rapid and stirring. It has a habit of sunning itself on rocks during the midday.The call in the breeding season is said to resemble that of the grey francolin of the plains. It has been compared in habit to that of the ptarmigan. It is said to feed on mosses, lichens, berries, and the shoots of plants. It also swallows grit to aid digestion.
The breeding season is May to July. The males are believed to be monogynous. The nest is a scrape on a hill-side under some sheltering rock, either scratched out by themselves or already available, and usually hidden with vegetation. The nest is sometimes lined with moss but well concealed although given away by the male. About 3 to 5 eggs, pale yellow in color and slightly glossy with reddish-brown markings on the rounded end, are laid, and the female incubates while the male stands sentinel. Parent birds may use distraction displays to draw the attention of predators. They call in a comparatively softer lower note to the young, which respond with chicken-like cheep calls.
Apart from Chelopistes lervicola described as an ectoparasite of this species, an Argasid tick Argas himalayensis has been noted.

Description

This partridge appears grey above and chestnut below with bright red bill and legs and the upperparts finely barred in black and white. In flight the pattern of dark brown primaries and secondaries with a narrow trailing white margin make them somewhat like the much larger Tibetan snowcock. The 14-feathered tail is dark and barred in white. There is variation in the shade and some birds have a nearly black crown. The primaries and secondaries are brown and the breast is deep chestnut. The abdomen has more white and the lower flanks and feathers around the vent are barred brown and white. The under-tail coverts are chestnut with black shaft streaks and white tips. Young birds have the lower parts mottled and the barring less distinct. The tarsus is feathered on the front of the leg half-way to the toes.It measures 38–40 cm in length. Females weigh 450–580 g; males, 550–700 g. Sexes are similar in plumage, female lacks spurs on the tarsus while the male has a blunt spur and sometimes a second incipient spur. Downy chicks have a resemblance to the chicks of the blood pheasant. Chicks are born with the tarsi feathered and the nostril opening is covered by feathers.

 

 

Origin of birds

Origin of birds

Based on fossil and biological evidence, most scientists accept that birds are a specialized subgroup of theropod dinosaurs, and more specifically, they are members of Maniraptora, a group of theropods which includes dromaeosaurs and oviraptorids, among others. As scientists have discovered more theropods closely related to birds, the previously clear distinction between non-birds and birds has become blurred. Recent discoveries in the Liaoning Province of northeast China, which demonstrate many small theropod feathered dinosaurs, contribute to this ambiguity.

The consensus view in contemporary paleontology is that the flying theropods, or avialans, are the closest relatives of the deinonychosaurs, which include dromaeosaurids and troodontids. Together, these form a group called Paraves. Some basal members of this group, such as Microraptor, have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal, have been able to glide, or both. Unlike Archaeopteryx and the non-avialan feathered dinosaurs, who primarily ate meat, recent studies suggest that the first avialans were omnivores.

Early evolution

The earliest known avialan fossils come from the Tiaojishan Formation of China, which has been dated to the late Jurassic period (Oxfordian stage), about 160 million years ago. The avialan species from this time period include Anchiornis huxleyi, Xiaotingia zhengi, and Aurornis xui. The well-known early avialan, Archaeopteryx, dates from slightly later Jurassic rocks (about 155 million years old) from Germany. Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds, but were later lost during bird evolution. These features include enlarged claws on the second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial maneuvering.
Avialans diversified into a wide variety of forms during the Cretaceous Period. Many groups retained primitive characteristics, such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves). While the earliest forms, such as Archaeopteryx and Jeholornis, retained the long bony tails of their ancestors, the tails of more advanced avialans were shortened with the advent of the pygostyle bone in the group Pygostylia. In the late Cretaceous, around 95 million years ago, the ancestor of all modern birds also evolved a better sense of smell.

Skeletal system

The skeleton consists of very lightweight bones. They have large air-filled cavities (called pneumatic cavities) which connect with the respiratory system. The skull bones in adults are fused and do not show cranial sutures. The orbits are large and separated by a bony septum. The spine has cervical, thoracic, lumbar and caudal regions with the number of cervical (neck) vertebrae highly variable and especially flexible, but movement is reduced in the anterior thoracic vertebrae and absent in the later vertebrae. The last few are fused with the pelvis to form the synsacrum. The ribs are flattened and the sternum is keeled for the attachment of flight muscles except in the flightless bird orders. The forelimbs are modified into wings.