Both of these factors, ancestry and adaptation, are likely to be important; in this lab you'll consider both of them. As it turns out, many of the unique features of birds have traditionally been interpreted as adaptations to flight. However, some major fossil discoveries have been made in recent years, overturning long-held beliefs about bird evolution. With that in mind, this lab isn't only about the bones of birds; it's about the ways that biologists understand the evolution of body structures. In birds, the last 5 to 6 caudal vertebrae are fused to form the pygostyle. [14] Some sources note that up to 10 caudal vertebrae may make up this fused structure. This structure provides an attachment point for tail feathers that aid in control of flight. [7] Highlighted in red is an intact keeled sternum of a dissected pigeon. In flying birds the sternum is enlarged for increased muscle attachment. Scapular girdle [ edit ] Adaptations to different food sources have shaped bird beaks into various forms. Let’s take a look at some interesting bill shapes and examples of the birds that have them. Gatesy, S.M. (2002). "19. Locomotor evolution on the line to modern birds". In Chiappe, L.M.; Witmer, L.M. (eds.). Mesozoic Birds: above the heads of dinosaurs. University California Press. pp.432–447. ISBN 978-0-520-20094-4. Scutes – the largest scales, usually on the anterior surface of the metatarsus and dorsal surface of the toes.

All species of birds with the exception of the penguin, have a small region of their lungs devoted to "neopulmonic parabronchi". This unorganized network of microscopic tubes branches off from the posterior air sacs, and open haphazardly into both the dorso- and ventrobronchi, as well as directly into the intrapulmonary bronchi. Unlike the parabronchi, in which the air moves unidirectionally, the air flow in the neopulmonic parabronchi is bidirectional. The neopulmonic parabronchi never make up more than 25% of the total gas exchange surface of birds. [56] Vocal Bird anatomy: Birds produce sounds through the air that passes through the Syrinx, which is shown close up in the bottom right.a b c Maina, John N. (2005). The lung air sac system of birds development, structure, and function; with 6 tables. Berlin: Springer. pp.3.2–3.3 "Lung", "Airway (Bronchiol) System" 66–82. ISBN 978-3-540-25595-6. Svihus, Birger (2014). "Function of the digestive system". The Journal of Applied Poultry Research. 23 (2): 306–314. doi: 10.3382/japr.2014-00937. The bones of the forelimb are modified for flight with feathers. Major modifications include restriction of the motion of the elbow and wrist joints to one plane, reduction of the number of digits, loss of functional claws, fusion of certain bones of the “hand” (the metacarpals and most of the carpals) into a carpometacarpus, and modification of the elements, especially those toward the tip of the limb (distal), for the attachment of feathers. The wing bones are hollow, and the cavity in the humerus is connected with the air-sac system. As a general rule, large flying birds have proportionally greater pneumaticity in the skeleton than small ones. The highly pneumatic bones of large flying birds are reinforced with bony struts at points of stress. The humerus, radius, and ulna are well developed. The secondary flight feathers are attached to the ulna, which thus directly transmits force from the flight muscles to these feathers and is therefore relatively heavier than the radius. Two small wrist bones are present: the radiale, or scapholunar, and the ulnare, or cuneiform. The former lies between the distal end of the radius and the proximal part (the part toward the body) of the carpometacarpus. When the elbow joint is flexed (bent), the radius slides forward on the ulna and pushes the radiale against the carpometacarpus, which in turn flexes the wrist. Thus the two joints operate simultaneously. The U-shaped ulnare articulates with the ulna and the carpometacarpus. Anatomists differ on which bones of the reptilian “hand” are represented in the bird’s wing. Embryological evidence suggests that the digits are II, III, and IV, but it is possible that they are actually I, II, and III. The carpometacarpus consists of fused carpals (bones of the wrist) and metacarpals (bones of the palm), metacarpals II and III (or III and IV) contributing the greater part of the bone. The bones of the “fingers” (phalanges) are reduced to one each on the outer and inner digits and two on the middle one. The primary flight feathers are attached to the carpometacarpus and digits, the number attached to each being characteristic of the various major groups of birds.

Their latest paper, authored by Anjali and postdoctoral researchers Ryan Felice and Marcela Randau, is suggesting a new model for how we can expect evolution to occur. The skin muscles help a bird in its flight by adjusting the feathers, which are attached to the skin muscle and help the bird in its flight maneuvers as well as aiding in mating rituals. Air passes unidirectionally through the lungs during both exhalation and inspiration, causing, except for the oxygen-poor dead space air left in the trachea after exhalation and breathed in at the beginning of inhalation, little to no mixing of new oxygen-rich air with spent oxygen-poor air (as occurs in mammalian lungs), changing only (from oxygen-rich to oxygen-poor) as it moves (unidirectionally) through the parabronchi. Flightless Birds". SKELETONS: Museum of Osteology (Oklahoma City). Archived from the original on 2018-06-27 . Retrieved 2018-05-02.

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Birds may not have external ears (pinnae) like we do, but they certainly do have ears. Their ears have large external openings on the side of their skull, below and behind their eyes. However, these openings are covered by feathers, so they are difficult to spot except on baby birds and species like Vultures with naked heads. Nectar is an energy-rich food source that is there for the taking - if you have the bill to reach it. Birds like Hummingbirds and Sunbirds use their long, fine bills to reach into tube-shaped flowers and access the sweet treat within. Seed eaters 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.” Birds have uncinate processes on the ribs. These are hooked extensions of bone which help to strengthen the rib cage by overlapping with the rib behind them. This feature is also found in the tuatara ( Sphenodon). Herrera, A. M; Shuster, S. G.; Perriton, C. L.; Cohn, M. J. (2013). "Developmental Basis of Phallus Reduction during Bird Evolution". Current Biology. 23 (12): 1065–74. doi: 10.1016/j.cub.2013.04.062. PMID 23746636.

Storer, Tracy I.; Usinger, R. L.; Stebbins, Robert C.; Nybakken, James W. (1997). General Zoology (6thed.). New York: McGraw-Hill. pp. 750–751. ISBN 978-0-07-061780-3. a b Sturkie, P.D. (1976). Sturkie, P. D (ed.). Avian Physiology. New York: Springer Verlag. p.201. doi: 10.1007/978-1-4612-4862-0. ISBN 978-1-4612-9335-4. S2CID 36415426.

Bird Skull

Zusi, R L (1984). "A Functional and Evolutionary Analysis of Rhynchokinesis in Birds". Smithsonian Contributions to Zoology. 395 (395): 1–40. doi: 10.5479/si.00810282.395. hdl: 10088/5187. 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. Feathers didn't evolve all at once. Numerous feathered dinosaur fossils have been found, with feathers ranging from simple hairlike structures to complex asymmetrical flight feathers resembling those of modern birds. Functionally, these feathers didn't all do the same thing, so it's likely that a variety of forces acted on the early evolution of feathers. Birds may be the only living group of animals with feathers, but that wasn't always true; birds are simply the last surviving members of a large group of feathered dinosaurs. For more information, see references under the evolution of feathers, below. Pneumatic bones

Kinesis of the cranium of a macaw with upper mandible lowered (left), with upper mandible raised (centre), and with forces acting upon the mandible (right). (more) Three distinct sets of organs perform respiration — the anterior air sacs (interclavicular, cervicals, and anterior thoracics), the lungs, and the posterior air sacs (posterior thoracics and abdominals). Typically there are nine air sacs within the system; [54] however, that number can range between seven and twelve, depending on the species of bird. Passerines possess seven air sacs, as the clavicular air sacs may interconnect or be fused with the anterior thoracic sacs. Dr Abzhanov said: “The skulls and brains of birds are dramatically different from those of adult non-avian dinosaurs and other reptiles, and we can show that these differences reflect how birds evolved to become species of forever-young dinosaurs.Stryer, Lubert (1995). In: Biochemistry (4thed.). New York: W.H. Freeman. pp.250–1. ISBN 0-7167-2009-4. These characteristics might seem to be unique to birds, but the surprising thing is that all of them have been found in nonflying fossil dinosaurs. While it's been clear for many years that birds descended from dinosaurs, researchers have only recently learned how much those prehistoric dinosaurs resembled birds. Some of these characteristics have traditionally been explained as adaptations to flight, but if the characteristics first appeared in dinosaurs long before the evolution of flight, then they weren't adaptations to flying. Nares are paired holes on the maxilla, usually located near the base of the bill. These are the bird’s nostrils, and most species draw their breath through the nares rather than the mouth. Tomia