Wang M., Zhou Z. A new adult specimen of the basalmost ornithuromorph bird Archaeorhynchus spathula (Aves: Ornithuromorpha) and its implications for early avian ontogeny. J. Syst. Palaeontol. 2017; 15:1–18. [ Google Scholar] Feathers are one of the defining characteristics of birds, and they play a key role in flight. However, recent paleontological studies show that feathers evolved before flight. What did these feathers do in the non-flying ancestors of birds?

From dinosaurs to birds: a tail of evolution Dana J. Rashid et al. 2014, EvoDevo 2014, 5:25. This article from EvoDevo (a journal dedicated to the study of evolution and development) discusses the possible genetic changes that might have led to one key step in the evolution of birds from their dinosaur ancestors: the shortening of the tail and the fusion of the last few caudal (tail) vertebrae. This is an example of a research paper that connects the worlds of Bio 6A (form & function) and Bio 6B (molecular biology).

Exhibition view: Hyungkoo Lee, The Objectuals, Sungkok Art Museum, Seoul (2004). Courtesy the artist. Phalanges: Phalanx is singular, phalanges is plural. Phalanges are finger bones, for birds or humans. Birds only have three "fingers"; their ancestors apparently had five, as do humans. The first one, roughly corresponding to a thumb, is called the alula. The alula bone supports a few feathers that can be moved separately from the others on the wing. (Incidentally, the word alula is Latin for "little wing." "Little Wing" is also the name of a classic song by Jimi Hendrix.) Florencio-Silva R., Sasso G.R.D.S., Sasso-Cerri E., Simões M.J., Cerri P.S. Biology of bone tissue: structure, function, and factors that influence bone cells. Biomed. Res. Int. 2015; 2015:421746. [ PMC free article] [ PubMed] [ Google Scholar] Benton MJ (2010) Studying Function and Behavior in the Fossil Record. PLoS Biol 8(3): e1000321. This brief, nontechnical article discusses the ways that paleontologists attempt to reconstruct the biology of extinct species. Furcula (wishbone): The furcula apparently corresponds to the clavicles (collarbones) of mammals. In birds, these bones are fused into a single structure. The furcula is springy; when a bird flies, it flexes in and out, storing and returning energy like a spring. This spring action wouldn't be possible if birds had two separate clavicles instead of a single furcula. It makes sense to view this structure as an adaptation to flight, but many nonflying dinosaurs (including Tyrannosaurus rex!) also had a furcula, so this fused structure didn't originate as an evolutionary response to flying. On the other hand, the furcula of T. rex and similar species was short and not structured to be springy. The furcula of birds did not originate as an adaptation to flight, but it has certainly been shaped by selection for efficient flying.

Bezuidenhout, A.J.; Groenewald, H.B.; Soley, J.T. (1999). "An anatomical study of the respiratory air sacs in ostriches" (PDF). Onderstepoort Journal of Veterinary Research. 66 (4): 317–325. PMID 10689704.

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Describe several ways that the skeletons of birds are similar to those of extinct dinosaurs, but different from mammals. How Dinosaurs Shrank and Became Birds. Singer, 2015. Quanta. Excellent exploration of the evolutionary processes behind this amazing transition.

Parasaurolophus cyrtocristatus skeleton on display at the Field Museum of Natural History, in Chicago. Life-size Parasaurolophus Skeleton Sculpture for SaleTibiotarsus: In birds, part of the tarsus is fused with the tibia. The tarsus in mammals consists of seven bones in the foot. It must be pointed out that there is some individual variation in this palatal complex, not only among bird groups, but also regarding the age of individual birds within these groups For instance, in the young of some gulls, crows, and hawks, the anterior margin of the pterygoid becomes detached from the rest and fuses with the palatine. These palatal types must be considered as of taxonomic value only when used as part of the diagnosis which is based on other osteological characters as well." X. Xu et al., “ An integrative approach to understanding bird origins,” Science 346, 6215 (12 December 2014). This recent review provides a detailed look at recent research on bird origins. From the abstract: "Recent discoveries of spectacular dinosaur fossils overwhelmingly support the hypothesis that birds are descended from maniraptoran theropod dinosaurs, and furthermore, demonstrate that distinctive bird characteristics such as feathers, flight, endothermic physiology, unique strategies for reproduction and growth, and a novel pulmonary system originated among Mesozoic terrestrial dinosaurs. The transition from ground-living to flight-capable theropod dinosaurs now probably represents one of the best-documented major evolutionary transitions in life history." Free abstract.

a b c d e f g h i j k l Kowalska-Dyrcz, Alina (1990). "Entry: noga [leg]". In Busse, Przemysław (ed.). Ptaki[ Birds]. Mały słownik zoologiczny [Small zoological dictionary] (in Polish). Vol.I (1sted.). Warsaw: Wiedza Powszechna. pp.383–385. ISBN 978-83-214-0563-6.

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Ateşoğlu S., Deniz M., Uslu A.I. Evaluation of the morphological characteristic and sex differences of sternum by multi-detector computed tomography. Folia. Morphol. (Warsz) 2018; 77:489–497. [ PubMed] [ Google Scholar] The various Iguanodon species are large herbivores, ranging from 6 to 11 metres (20 to 36 feet) in length, and averaging about 5 tonnes (5.5 tons) in weight.