Bardskull

Product Information

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. 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 ]

Sawyer, R.H.; Knapp, L.W. (2003). "Avian Skin Development and the Evolutionary Origin of Feathers". Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. 298 (1): 57–72. doi: 10.1002/jez.b.26. PMID 12949769. Many seabirds have glands near the eyes that allow them to drink seawater. Excess salt is eliminated from the nostrils. Many desert birds get the water that they need entirely from their food. The elimination of nitrogenous wastes as uric acid reduces the physiological demand for water, [75] as uric acid is not very toxic and thus does not need to be diluted in as much water. [76] 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.” They have a greatly elongate tetradiate pelvis, similar to some reptiles. The hind limb has an intra-tarsal joint found also in some reptiles. There is extensive fusion of the trunk vertebrae as well as fusion with the pectoral girdle.a b c Bhullar, Bhart-Anjan S.; Marugán-Lobón, Jesús; Racimo, Fernando; Bever, Gabe S.; Rowe, Timothy B.; Norell, Mark A.; Abzhanov, Arhat (2012-05-27). "Birds have paedomorphic dinosaur skulls". Nature. 487 (7406): 223–226. Bibcode: 2012Natur.487..223B. doi: 10.1038/nature11146. ISSN 1476-4687. PMID 22722850. S2CID 4370675. It is thought that when the dinosaurs went extinct the Earth was emptied of species, allowing the surviving birds to fill the roles that many of their extinct relatives once occupied. Through this process they became all the wonderful and weird varieties we now see. a b c d Scott, Graham R. (2011). "Commentary: Elevated performance: the unique physiology of birds that fly at high altitudes". Journal of Experimental Biology. 214 (15): 2455–2462. doi: 10.1242/jeb.052548. PMID 21753038.

When you look at the vast diversity of life on Earth, from bees to blue whales, it might feel like evolution can occur in limitless, random directions. But the team say that is not the case, because there are constraints on what evolution can do. When we think about how the animals of today might evolve in the future, it may be that nature only has a limited number of options available. The bursa of fabricius, also known as the cloacal bursa, is a lymphoid organ which aids in the production of B lymphocytes during humoral immunity. The bursa of fabricius is present during juvenile stages but curls up, and in the sparrow is not visible after sexual maturity. [92] Anatomy [ edit ] 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 Lucas, Alfred M. (1972). Avian Anatomy – integument. East Lansing, Michigan, USA: USDA Avian Anatomy Project, Michigan State University. pp.67, 344, 394–601.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

Article text (excluding photos or graphics) available under an Attribution-NonCommercial-ShareAlike Creative Commons license. Male birds have two testes which become hundreds of times larger during the breeding season to produce sperm. [77] The testes in birds are generally asymmetric with most birds having a larger left testis. [78] Female birds in most families have only one functional ovary (the left one), connected to an oviduct — although two ovaries are present in the embryonic stage of each female bird. Some species of birds have two functional ovaries, and the kiwis always retain both. [79] [80] Bird’s bills vary in form just as dramatically as they do in size, but why do birds have such wildly different bill shapes? The rows of scutes on the anterior of the metatarsus can be called an "acrometatarsium" or "acrotarsium".

A huge variety in forms

Now look at the dinosaurs. Allosaurus, Tyrannosaurus, and Velociraptor are are clearly dinosaurs; after all, dinosaurs like these were featured in the Jurassic Park movies. Notice that there is no clade that includes all these dinosaurs but does not include birds. If Dinosauria is a valid taxonomic group (and it is), then it has to include birds. As it turns out, not all the dinosaurs became extinct; birds are the last surviving dinosaurs. Most people tend to think that the age of dinosaurs ended long ago; however, given that there are over 10,000 species of birds on Earth (compared to 5500 species of mammals), one could say that we are still living in the age of dinosaurs. a b Kurochkin, E. N. (1995). "Synopsis of Mesozoic Birds and Early evolution of Class Aves". Archaeopteryx: Jahreszeitschrift der Freunde des Jura-Museums Eichstätt. 13: 47–66. ISSN 0933-288X. OCLC 85132179. Scientists have been trying to decipher the intricacies of this process for centuries. A research team in the Museum, led by Prof Anjali Goswami, is working to find out more about how and why we evolved the way that we have. Calder, William A. (1996). Size, Function, and Life History. Mineola, New York: Courier Dove Publications. p.91. ISBN 978-0-486-69191-6.

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. The avian stomach is composed of two organs, the proventriculus and the gizzard that work together during digestion. The proventriculus is a rod shaped tube, which is found between the esophagus and the gizzard, that secretes hydrochloric acid and pepsinogen into the digestive tract. [65] The acid converts the inactive pepsinogen into the active proteolytic enzyme, pepsin, which breaks down specific peptide bonds found in proteins, to produce a set of peptides, which are amino acid chains that are shorter than the original dietary protein. [66] [67] The gastric juices (hydrochloric acid and pepsinogen) are mixed with the stomach contents through the muscular contractions of the gizzard. [68] Gizzard [ edit ]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. As well as this, the parts of the skull that are evolving fastest tend to be made of specific types of tissue. Anything made of older, ancestral tissue types are evolving more slowly, whereas bones made up of a mix of tissues evolve the fastest. This suggests that diversity in developmental origin creates diversity in form. Why did non-flying dinosaurs have pneumatic bones? The air spaces in bones don't only affect the mass and stiffness of the bones. These air spaces are connected to the system of air sacs that runs throughout the bird's body. As you learned in lecture (I hope), birds have one-way air flow through their lungs, aided by air sacs that help to pump the air in and out. These air sacs extend into the bones, and air can move