Feather development
Feather development occurs in the
Anatomy of a feather
Feathers are products of the epidermis and
Evolution of feathers
Feathers are sometimes referred to as “elaborate reptile scales” just as birds are sometimes viewed as a subset of reptiles instead of their own category. Although this is a simplification, it originates from bird's
In 1861, a group of German quarry workers found the fossil of Archaeopteryx, which had feathers like modern birds, but also teeth in its mouth, a long, bony wing, and claws on its wings like a reptile. Archaeopteryx seems to be a transitional animal from reptile to bird. However, Archaeopteryx had already rather developed feathers, which didn't help to show how the feathers had evolved in the first place. In 1996, the missing fossil to help show the evolution of feathers was found. Sinosauropteryx was covered in thin, hollow filaments that covered its back and tail. Now, after finding many dinosaurs with primitive feathers, it is believed that feathers started out as these thin, hollow filaments, and eventually evolved into the fluffy coats of feathers seen on modern birds.[3]
There are a few theories for the reasons feathers evolved in the first place, if not for flight. The first is that they served a purpose as insulation. Theropods have been found covering their nests with their forelimbs, thought to be sheltering their young. Feathers known to be found on theropods would have played an important role for insulation. Another popular theory is that quick, bipedal dinosaurs used their feathers to run faster. It's possible that the feathers assisted the dinosaurs running up inclines, and this advantage of speed eventually lead to flight. The arboreal theory suggests that animals that lived in trees found it quicker and more energy efficient to leap from tree to tree instead of running down a tree, across the ground to another tree, and back up the new tree. This leaping eventually lead to gliding, and flight.[1]
Another newer theory is that feathers were selected for sexually.[2] Their bold plumage with its patterns, coloration, and even iridescent colors were to attract the opposite sex, which is very common in modern birds today. By uncovering new technology to look and analyze well-preserved melanosomes, scientists can reconstruct what the feathers on fossilized dinosaurs would have looked like, and they look rather flamboyant.
More current theories of the original purpose/advantage of flight involve more than one of these theories in combination with each other. Ken Dial, a flight researcher at the
Steps of feather development
Feathers develop from the dermal papillae. Feathers begin to form from feather follicles, which are invaginations starting in the epidermis down to the
Types of feathers
There are six different types of feathers, which are flight, contour, down, semiplumes, filoplumes, and bristle feathers.[4] [5] [6]
Pennaceous feathers
The wing feathers can in turn be broken down into further types (primary, secondary and tertiary). In general, they are long and asymmetrical with a thin leading edge allowing for strong stable feathers during flight. Flight feathers are connected to the bone with ligaments allowing them to be moved with precision and ensuring they remain tightly attached to the bird. The primaries are at the far (wrist) end of the wing and provide forward thrust during takeoff and flight. The secondaries are in the middle of the wing and attach to the ulna and form an airfoil which provides lift. The tertiaries are located closest to the body.
The tail feathers are used to control flight acting as rudder and brake, only some of these feathers are as firmly attached as the bird's primaries.
Contour feathers are arranged on the body of the bird in the manner of roof tiles. The tips of these feathers are waterproof and help protect the bird from the elements, while the inner parts of the feather near the bird's body are more downy. Wing contour feathers (known as coverts) help with the aerodynamics of the wing by covering where the flight feathers attach to the bone.
Plumulaceous feathers
Plumulaceous feathers, otherwise known as downy feathers, lack barbules and hooklets. Normally, they are fluffy and used for insulation. There are special types of down feathers that, when disintegrated, can form keratin powder, which can be used to waterproof feathers. Birds can use this ability for a variety of reasons, but the main reason is for insulation against cold and/or water, especially for the birds that dive into or sit on water. There are four kinds of these feathers.
Semiplumes are usually not visible as they are hidden by the contour feathers. Their appearance is that of a loose downy, but stiff feather. They consist of a rachis, barbs and barbules, however they do not have hooklets. Their purpose is insulation and aerodynamics. Down is similar to semiplume, however they have a very short or missing rachis.
Filoplumes are thin, hair-like feathers with a long rachis and very few barbs near the tip. They are located next to other feathers and, while their function is not fully understood, they are thought to serve a sensory function allowing the bird to react to the positioning of its contour and flight feathers.
Bristle feathers have a stiff rachis with a few barbs near the base. They are located around the eyes and mouth; it is believed that they have a protective and sensory function.
Not all birds that have feathers use them for flight. Penguins use them for insulation against the cold of the air and water. Whereas, the ostrich utilizes its feathers for mating and for fluffing, which allows them to release heat and cool down.
References
- ^ ISBN 978-0078023026.
- ^ ISBN 978-1936221448.
- PMID 19139401.
- ^ "Bird Feather Types, Anatomy, Molting, Growth, and Color". www.peteducation.com. Archived from the original on 2017-02-09. Retrieved 2016-12-01.
- ^ "Everything You Need To Know About Feathers". www.allaboutbirds.org. Retrieved 2023-07-27.
- ^ "Types of Bird Feathers". www.paulnoll.com. Retrieved 2023-07-27.