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Theory Of Flight
Around 350 BCE, Aristotle and other philosophers of the time attempted to explain the aerodynamics of avian flight. Even after the discovery of the ancestral bird '' Archaeopteryx'' which lived over 150 million years ago, debates still persist regarding the evolution of flight. There are three leading hypotheses pertaining to avian flight: Pouncing Proavis model, Cursorial model, and Arboreal model. In March 2018, scientists reported that '' Archaeopteryx'' was likely capable of flight, but in a manner substantially different from that of modern birds. Flight characteristics For flight to occur, four physical forces (thrust and drag, lift and weight) must be favorably combined. In order for birds to balance these forces, certain physical characteristics are required. Asymmetrical wing feathers, found on all flying birds with the exception of hummingbirds, help in the production of thrust and lift. Anything that moves through the air produces drag due to friction. The aerodynam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Archaeopteryx Lithographica (Berlin Specimen)
''Archaeopteryx'' (; ), sometimes referred to by its German name, "" ( ''Primeval Bird''), is a genus of bird-like dinosaurs. The name derives from the ancient Greek (''archaīos''), meaning "ancient", and (''ptéryx''), meaning "feather" or "wing". Between the late 19th century and the early 21st century, ''Archaeopteryx'' was generally accepted by palaeontologists and popular reference books as the oldest known bird (member of the group Avialae). Older potential avialans have since been identified, including ''Anchiornis'', ''Xiaotingia'', and ''Aurornis''. ''Archaeopteryx'' lived in the Late Jurassic around 150 million years ago, in what is now southern Germany, during a time when Europe was an archipelago of islands in a shallow warm tropical sea, much closer to the equator than it is now. Similar in size to a Eurasian magpie, with the largest individuals possibly attaining the size of a raven, the largest species of ''Archaeopteryx'' could grow to about in len ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of two solid surfaces in contact. Dry friction is subdivided into ''static friction'' ("stiction") between non-moving surfaces, and ''kinetic friction'' between moving surfaces. With the exception of atomic or molecular friction, dry friction generally arises from the interaction of surface features, known as asperities (see Figure 1). *Fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. *Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces. *Skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body. *Internal friction is the force resisting motion between the elements making up a so ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Samuel Wendell Williston
Samuel Wendell Williston (July 10, 1852 – August 30, 1918) was an American educator, entomologist, and paleontologist who was the first to propose that birds developed flight cursorially (by running), rather than arboreally (by leaping from tree to tree). He was a specialist on the flies, Diptera. He is remembered for Williston's law, which states that parts in an organism, such as arthropod limbs, become reduced in number and specialized in function through evolutionary history. Early life Williston was born in Boston, Massachusetts to Samuel Williston and Jane A. Williston née Turner. As a young child, Williston's family travelled to Kansas Territory in 1857 under the auspices of the New England Emigrant Aid Company to help fight the extension of slavery. He was raised in Manhattan, Kansas, attended public high school there, and graduated from Kansas State Agricultural College (now Kansas State University) in 1872, afterwards receiving a Master of Arts from that instituti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rachis
In biology, a rachis (from the grc, ῥάχις [], "backbone, spine") is a main axis or "shaft". In zoology and microbiology In vertebrates, ''rachis'' can refer to the series of articulated vertebrae, which encase the spinal cord. In this case the ''rachis'' usually forms the supporting axis of the body and is then called the spine or vertebral column. ''Rachis'' can also mean the central shaft of pennaceous feathers. In the gonad of the invertebrate nematode '' Caenorhabditis elegans'', a rachis is the central cell-free core or axis of the gonadal arm of both adult males and hermaphrodites where the germ cells have achieved pachytene and are attached to the walls of the gonadal tube. The rachis is filled with cytoplasm. In botany In plants, a rachis is the main axis of a compound structure. It can be the main stem of a compound leaf, such as in ''Acacia'' or ferns, or the main, flower-bearing portion of an inflorescence above a supporting peduncle. Where it subdivides ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sapeornis
''Sapeornis'' is a monotypic genus of avialan which lived during the early Cretaceous period ( late Barremian to early Aptian, roughly 125-120 mya). ''Sapeornis'' contains only one species, ''Sapeornis chaoyangensis''. Description ''Sapeornis'' was large for an early avialan, about long in life, excluding the tail feathers. The hand of ''Sapeornis'' was far more derived than that of ''Archaeopteryx''. It had three fingers, the outer ones with two and the middle one with three phalanges, and a well-fused carpometacarpus. Its arms were about half again as long as the legs, suggesting a large wing area. On the other hand, its shoulder girdle was apparently ill-adapted to flapping flight and its furcula was unusual, with a hypocleidum similar to more advanced avialans but a general anatomy even more basal than in ''Archaeopteryx''. The humerus was large and bore holes, apparently to save weight, as in the Confuciusornithidae. The skull has a handful of teeth in the upper jawtip ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Confuciusornis
''Confuciusornis'' is a genus of basal crow-sized avialan from the Early Cretaceous Period of the Yixian and Jiufotang Formations of China, dating from 125 to 120 million years ago. Like modern birds, ''Confuciusornis'' had a toothless beak, but closer and later relatives of modern birds such as ''Hesperornis'' and ''Ichthyornis'' were toothed, indicating that the loss of teeth occurred convergently in ''Confuciusornis'' and living birds. It is the oldest known bird to have a beak. It was named after the Chinese moral philosopher Confucius (551–479 BC). ''Confuciusornis'' is one of the most abundant vertebrates found in the Yixian Formation, and several hundred complete specimens have been found. History of discovery In November 1993, the Chinese paleontologists Hou Lianhai and Hu Yoaming of the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) at Beijing, visited fossil collector Zhang He at his home in Jinzhou, where he showed them a fossil bird specimen t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microraptor
''Microraptor'' (Greek, μικρός, ''mīkros'': "small"; Latin, ''raptor'': "one who seizes") is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China. They date from the early Cretaceous Jiufotang Formation (Aptian stage), 125 to 120 million years ago. Three species have been named (''M. zhaoianus'', ''M. gui'', and ''M. hanqingi''), though further study has suggested that all of them represent variation in a single species, which is properly called ''M. zhaoianus''. ''Cryptovolans'', initially described as another four-winged dinosaur, is usually considered to be a synonym of ''Microraptor''. Like ''Archaeopteryx'', well-preserved fossils of ''Microraptor'' provide important evidence about the evolutionary relationship between birds and earlier dinosaurs. ''Microraptor'' had long pennaceous feathers that formed aerodynamic surfaces on the arms and tail but also on the legs. This led paleon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proavis
Proavis refers to a hypothetical extinct species or hypothetical extinct taxon and was coined in the early 20th century in an attempt to support and explain the hypothetical evolutionary steps and anatomical adaptations leading from non-avian theropod dinosaurs to birds. The term has also been used by defenders of the thecodontian origin of birds. History The term "Proavis" was first coined, although under the form "Pro-Aves", by English osteologist and zoologist William Plane Pycraft in "The Origin of Birds", a 1906 article published in the magazine ''Knowledge and Scientific News''. Pycraft added to his article his own drawn depiction of the hypothetical animal, a restoration entitled "One of the Pro-Aves". Pycraft's "Pro-Avis" (singular of "Pro-Aves") was arboreal, as suggested Professor Osborn six years before, in 1900, in an article dealing with the hypothetical common ancestors of dinosaurs and birds. Pycraft assumed that birds had developed as tree-dwelling dinosaurs, gl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Furcula
The (Latin for "little fork") or wishbone is a forked bone found in most birds and some species of non-avian dinosaurs, and is formed by the fusion of the two pink clavicles. In birds, its primary function is in the strengthening of the thoracic skeleton to withstand the rigors of flight. In birds The furcula works as a strut between a bird's shoulders, and articulates to each of the bird's scapulae. In conjunction with the coracoid and the scapula, it forms a unique structure called the triosseal canal, which houses a strong tendon that connects the supracoracoideus muscles to the humerus. This system is responsible for lifting the wings during the recovery stroke. As the thorax is compressed by the flight muscles during downstroke, the upper ends of the furcula spread apart, expanding by as much as 50% of its resting width, and then contracts. X-ray films of starlings in flight have shown that in addition to strengthening the thorax, the furcula acts like a spring in the pe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bird Anatomy
Bird anatomy, or the physiological structure of birds' bodies, shows many unique adaptations, mostly aiding flight. Birds have a light skeletal system and light but powerful musculature which, along with circulatory and respiratory systems capable of very high metabolic rates and oxygen supply, permit the bird to fly. The development of a beak has led to evolution of a specially adapted digestive system. Skeletal system Birds have many bones that are hollow ( pneumatized) with criss-crossing struts or trusses for structural strength. The number of hollow bones varies among species, though large gliding and soaring birds tend to have the most. Respiratory air sacs often form air pockets within the semi-hollow bones of the bird's skeleton. The bones of diving birds are often less hollow than those of non-diving species. Penguins, loons, and puffins are without pneumatized bones entirely. Flightless birds, such as ostriches and emus, have pneumatized femurs and, in the case of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cerebellum
The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebellum plays an important role in motor control. It may also be involved in some cognition, cognitive functions such as attention and language as well as emotion, emotional control such as regulating fear and pleasure responses, but its movement-related functions are the most solidly established. The human cerebellum does not initiate movement, but contributes to Motor coordination, coordination, precision, and accurate timing: it receives input from sensory systems of the spinal cord and from other parts of the brain, and integrates these inputs to fine-tune motor activity. Cerebellar damage produces disorders in Fine motor skill, fine movement, Equilibrioception, equilibrium, Human positions, posture, and motor learning in humans. Anatomica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Keel (bird)
A keel or carina (plural carinae) in bird anatomy is an extension of the sternum (breastbone) which runs axially along the midline of the sternum and extends outward, perpendicular to the plane of the ribs. The keel provides an anchor to which a bird's wing muscles attach, thereby providing adequate leverage for flight. Not all birds have keels; in particular, some flightless birds lack a keel structure. Without a keel a bird will not be able to fly. Some flightless birds have a keel, such as the penguin; but in the penguin's case, its wings are too small for its body, so flight would require flapping its wings too fast to be practical. Historically, the presence or absence of a pronounced keel structure was used as a broad classification of birds into two orders: Carinatae (from ''carina'', "keel"), having a pronounced keel; and ratites (from ''ratis'', "raft"referring to the flatness of the sternum), having a subtle keel structure or lacking one entirely. However, this class ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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