Long assumed to have evolved from reptilian scales, the first feathers of birds are now thought by some scientists to have been entirely new structures erupting from skin patches called placodes. First simple hollow tubes, hey later evolved into more elaborate structures with interconnected barbs forming flat vanes, enabling flight. Feathers are complex designed structures required for flight, and are today found only on birds. In 2,009, Chinese scientists announced the discovery of a bristly-backed creature, Tianyulong, on the ornithischian branch of the dinosaur family tree that raised the astonishing possibility that the ancestor of all dinosaurs had hairlike feathers and that some species lost them later in evolution. The origin of feathers could be pushed back further still if the “fuzz” found on some pterosaurs is confirmed to be feathers, since these flying reptiles share an even older ancestor with dinosaurs. There is an even more astonishing possibility. The closest living relatives of birds, dinosaurs, and pterosaurs are alligators and crocodilians. Although they do not have feathers today, these scaly beasts, scientists discovered the same gene in alligators is involved in building feathers in birds suggests that perhaps their ancestors did, 250 million years ago, before the lineages diverged. So the question scientists ask is – Not how the birds got their feathers, but how alligators lost theirs. It is believed by most scientists, that the insulating effect was the primary force during the evolution of feathers. Feathers have enabled birds to refine flight to an art form matched by no other organism alive today.
Birds are unique creatures having wings, feathers, hollow bones, and other adaptations for an ariel lifestyle. Fight consumes a great deal of energy and consequently these warm blooded animals have high metabolic rates. Many of their bones are fused for strength and stability. The evolution of feathers, with an asymmetrical shape, like those of Archaeopteryx, further enhance the flight capabilities of early birds. Corwin Sullivan and his colleagues at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China have found in theropods that were closely related to living birds, a particular wristbone was wedge-shaped, allowing them to bend their hands. Anchiornis’s wrist bone was so wedge-shaped that it could fold its arms at its sides, keeping its arm feathers off the ground as it walked. Modern birds use a similar bone in flight, drawing their wings toward their bodies during an upstroke. If these scientists are right, this crucial flight feature evolved long before birds took wing. It is an example of what evolutionary biologists call exaptation: borrowing an old body part for a new job. It now looks like bird flight was made possible by a whole string of such exaptations stretching across millions of years, long before flight itself arose. For example, Luis Chiappe, an expert on early birds at the Natural History Museum of Los Angeles, California, suggests that flight like occurred as a by-product of arm flapping in ground dwelling dinosaurs, as the predecessors of birds used their feathered arms to increase their running speed or balance themselves as they made fast turns. Over generations, muscles used for such actions evolved to become stronger, bodies smaller and lighter, and feathers longer and more aerodynamic. Eventually the flapping of feathery arms evolved into the repetitive strokes of wings. “Even Archaeopteryx, which is often cast as a poor flier, could have taken off from the ground ,” says Luis Chiappe.
In 2,009 Jakob Vinther and his colleagues had discovered microscopic pigment sacs, called melanosomes, in the feathers of extinct birds. In 2,010 Vinther decoded the full-body coloration of Anchiornis: rusty red crown, dark grey body, and black-and-white striped wings. Scientists at Arizona State University are studying – How the consumption of carotenoids can improve or ‘tune’ birds colour, promote the health of offspring as they develop in the egg, and possibly improve male sperm quality. In today’s birds, feather colour are a result of pigments. Melanins are brown/black pigments. In addition to adding colour to the feather it makes feathers denser and more resilient to wear and breakdown by sunlight. Porphynne is the red and green pigments that are produced by cells in the feather folicle. Carotenoids are synthesized organic pigments produced in plants, and absorbed by the bird’s digestive systems, and then taken up by the cells of the follicle as the feather is developing. Species, such as, the Northern Cardinals, their colourful feathers are a result of a diet rich in carotenoids. Like the scales of reptiles, and those on the feet of birds, feathers are made of keratin, a fibrous protein. In Parrots, when the sheaths or barbs of feathers disintegrate, they form a fine keratin powder, which the bird can spread over its feathers as a water-proofing. Feathers vary considerably in structure and function. Feathers are arranged in major distinct tracts, called pterylae. The featherless areas between the pterylae are called aptena. Contour feathers form most of the surface of the bird, streamlining it for flight and often waterproofing it. They consist of a tapered central shaft, the rachis, with pairing branches (barbs) on each side. Afterfeathers (hypopenge), at the base of the vane in an area called the distal umbilicus. They are barbs without hooks, which help trap air and offer insulation. Down feathers have loose-webbed barbs, all rising from the tip of a very short shaft. Filoplumes are hair-like feathers with a few soft barbs at the top. Bristlelike vaneless feathers occur around the mouth, eyes and nostrils of birds.
When you look up to the sky and spot a bird, next time, you will be able to understand how its feathers have evolved, protect it and make it possible for the bird to fly. That is, down to the microscopic level, you can appreciate the complexity of specialization that makes birds such a unique part of the animal kingdom.
Source: National Geographic
Doug Worrrall Photography