Feathers are essentially a highly modified form of the scales found on other reptiles. Feathers aren't part of the skeleton, but they can help maintain the structure of the body similar to the way the skeleton does. For example, compare the wings of a bird to the wings of a bat. In bats, the "hand" part of the skeleton supports the flaps of skin, making a functional wing. In birds, the "hand" part is proportionally much shorter. The tip of the wing is composed only of the large primary flight feathers. As a result, the number of bones in the bird forelimb has been reduced compared to their ancestors. In fact, bird skeletons generally have many bones eliminated, reduced in size, or fused together compared to mammals, to the extent that a bird's feathers commonly weigh more than its bones. Birds have kinetic skulls, and at least some species can move their maxilla and mandible independently. While this flexibility does allow greater movement between the jaws, it comes at a cost to bite strength. Adaptations for Hearing and Sight

DÜZLER, A.; ÖZGEL, Ö.; DURSUN, N. (2006). "Morphometric analysis of the sternum in avian species" (PDF). Turkish Journal of Veterinary and Animal Sciences. 30: 311–314. ISSN 1303-6181. Archived from the original (PDF) on 2013-11-12 . Retrieved 2013-03-01.The partially digested and pulverized gizzard contents, now called a bolus, are passed into the intestine, where pancreatic and intestinal enzymes complete the digestion of the digestible food. The digestion products are then absorbed through the intestinal mucosa into the blood. The intestine ends via the large intestine in the vent or cloaca which serves as the common exit for renal and intestinal excrements as well as for the laying of eggs. [69] However, unlike mammals, many birds do not excrete the bulky portions (roughage) of their undigested food (e.g. feathers, fur, bone fragments, and seed husks) via the cloaca, but regurgitate them as food pellets. [70] [71] Drinking behaviour [ edit ] Calder, William A. (1996). Size, Function, and Life History. Mineola, New York: Courier Dove Publications. p.91. ISBN 978-0-486-69191-6. Article text (excluding photos or graphics) available under an Attribution-NonCommercial-ShareAlike Creative Commons license. The rows of scutes on the anterior of the metatarsus can be called an "acrometatarsium" or "acrotarsium". To better understand the origins of birds’ unique skulls during their evolution from more primitive reptiles, Dr Abzhanov and colleagues from Yale University have now analysed the relationship between brain and skull.

It may be easier to say what Bardskull is not. It’s not a memoir. It’s not poetry. It’s not a compendium of myths and ancient wisdom. It is, rather, all of these things, plus some faux-naive drawings, loosely structured around an autofictional account of several journeys that oral storyteller Martin Shaw seems to have undertaken on Dartmoor over the course of 101 days, a kind of wilderness journey. Or in Shaw-speak: “I walked out one summer morning and barely ceased till St George’s Day of the next year … These are words from the rough, from the stomp. Things hurtled through me, old things. I am not the same.” The thoracic vertebrae number between 5 and 10, and the first thoracic vertebra is distinguishable due to the fusion of its attached rib to the sternum while the ribs of cervical vertebrae are free. [7] Anterior thoracic vertebrae are fused in many birds and articulate with the notarium of the pectoral girdle. [13] Diagram of a general bird pelvic girdle skeleton including the lower vertebral column sections. Note that the caudal vertebrae (5–10) are not fused in this diagram but can be in certain species. Synsacrum [ edit ] A bird’s beak is one of its most defining features and one of the first things birdwatchers look at when putting a name to a face. Each bill is different, and they vary in size between barely noticeable structures like the beak of the Redpoll and the Long-tailed Tit and oversized bills like those of the Woodstork and the Toucans. So, as birds evolved to live in different environments and feed on various food sources, their bills evolved into shapes and sizes best suited to capture/collect and process that food. This section needs additional citations for verification. Please help improve this article by adding citations to reliable sourcesin this section. Unsourced material may be challenged and removed. ( September 2018) ( Learn how and when to remove this template message)Although this general rule still stands, since that time, observations have been made of a few exceptions in both directions. [72] [74] The team found that the structure of the skull is divided up into parts, each with a different evolutionary history and future. The rhamphotheca may be tough or leathery, and it grows continuously throughout the bird’s life. Structurally, this covering is a modified skin layer with an outer layer rich in keratin, the same material that makes up our fingernails. Nares The mandible and maxilla are extensions of the bird’s skull, although they are not attached in the same way as our jaws. Instead, the bird’s upper and lower jaw move independently of the skull, which allows birds to open their bill very wide. The mandible and maxilla are composed of fused bones and do not grow throughout the bird’s life. Rhamphotheca

Du Brul, E. Lloyd (1962). "The general phenomenon of bipedalism". American Zoologist. 2 (2): 205–208. doi: 10.1093/icb/2.2.205. Despite the wide variety of colors, shapes, and sizes, all bird beaks consist of the upper jaw (maxilla), lower jaw (mandible), and the keratinized outer layer (Rhamphotheca) that covers them. Let’s take a closer look at some of the most important features of a bird’s beak. Mandible and Maxilla The bird skull is a collection of fused bones that support the brain and sensory organs. It has evolved to be strong but lightweight, which is essential for flight. The various bones of the skull are difficult to differentiate because they fuse almost seamlessly. Nevertheless, we can separate the avian skull into the following components:The urine collected by the kidney is emptied into the cloaca through the ureters and then to the colon by reverse peristalsis. Dr Abzhanov said: “One other useful outcome of this survey of skulls from across reptile evolution was a better ability to recognise the (often disputed) evolutionary fates of individual cranial bones, especially during the dramatic reptile to bird transition.” Changes in the hindlimbs did not affect the location of the forelimbs, which in birds remained laterally spaced, and in non-avian dinosaurs they switched to a parasagittal orientation. [36] At the same time, the forelimbs, freed from the support function, had ample opportunities for evolutionary changes. Proponents of the running hypothesis believe that flight was formed through fast running, bouncing, and then gliding. The forelimbs could be used for grasping after a jump or as "insect trapping nets", animals could wave them, helping themselves during the jump. According to the arboreal hypothesis, the ancestors of birds climbed trees with the help of their forelimbs, and from there they planned, after which they proceeded to flight. [38] Muscular system [ edit ] The supracoracoideus works using a pulley-like system to lift the wing while the pectorals provide the powerful downstroke