John Alan Feduccia (born 25 April 1943) is a paleornithologist, specializing in the origins and phylogeny of birds. He is now Professor Emeritus at the University of North Carolina. Feduccia's principal authored works include two books, The Age of Birds and The Origin and Evolution of Birds, and numerous papers in various ornithological and biological journals. Feduccia is best known for his criticisms of the widely held view that birds originated from and are deeply nested within Theropoda, and are therefore living theropod dinosaurs. He has argued for an alternative theory in which birds share a common stem-ancestor with theropod dinosaurs among more basal archosaurian lineages, with birds originating from small arboreal archosaurs in the Triassic.
Feduccia graduated with a B.S. from Louisiana State University, taking ornithological expeditions to Honduras, El Salvador and Peru. He received his M.A. and Ph.D. (1969) from the University of Michigan.
Academic career and research
Feduccia's research has focused on ornithology, evolutionary biology, vertebrate history and morphogenesis, and the tempo and mode of the Tertiary vertebrate radiation. His early work in the 1970s focused on clarification of the evolutionary history of modern birds (Neornithes), focusing, in particular, on the importance of the identification of conserved morphological characters that might elucidate phylogeny more readily than more functionally correlated characters. Using this approach, in a series of publications, Feduccia analyzed the morphology of the bony stapes, the ear ossicle of birds, to help elucidate the interrelationships of passeriform birds. This approach was extended to the analysis of non-passeriform birds as well, including owls and the shoebill, also known as the whalebill (Balaeniceps rex). Other studies in the 1970s focused on the analysis of the Tertiary avian radiation, with a particular focus on the origin and relationships of waterfowl Anseriformes. Based on his analysis of the osteology of the Paleocene and Eocene duck Presbyornis, represented in large quantities from Eocene deposits from outcrops of the Green River Formation in Utah and Wyoming, Feduccia concluded that Presbyornis represents a shorebird-duck mosaic and that waterfowl evolved from shorebirds (Charadriiformes). This is contrary to the more widely held view that waterfowl are most closely related to chickens, turkeys, and related fowl (Galliformes), but Feduccia argues that this alternative phylogeny is unsupported by fossil evidence, and he suggests that any similarities between anseriform and galliform birds are attributable to homoplasy. Partly based on his analysis of the osteology of Presbyornis, Feduccia also argued that flamingos, the phylogenetic relationships of which remain disputed, with some recent studies suggesting a sister-group relationship with grebes, were actually derived from shorebirds. Feduccia summarized his position in the second edition of his book The Origin and Evolution of Birds: "The study of Presbyornis planted the idea that shorebirds are the basic ancestral stock for both flamingolike birds and the anseriformes, ducks and their allies...".
Feduccia's early work on flamingos and waterfowl contributed to the development of his hypothesis that there was an explosive Tertiary adaptive radiation of neornithine birds following the extinction event at the end of the Cretaceous. According to this hypothesis, modern orders of birds initially radiated principally from a lineage of "transitional shorebirds", represented by the shorebird form-family Graculavidae, from the Cretaceous-early Paleogene, that managed to survive the Cretaceous extinction event, perhaps through eking out a living along marginal shoreline environments. This radiation is hypothesized to have been very rapid, as many orders of modern birds have fossil representatives from the early Tertiary. Feduccia has suggested that this rapid adaptive radiation of modern birds, compressed into such a short period of geologic time, might seriously obscure interordinal relationships and make elucidation of the phylogeny of modern birds particularly difficult, barring the isolation of conserved characters or mosaic fossils demonstrating transitional character states bridging extant orders. This reiterates an early theme from his research in the 1970s, in which Feduccia had repeatedly emphasized the importance of homoplasy in evolution, and its ability to confound the interpretation of phylogeny. This has also been a theme in his study of flightlessness in birds, a phenomenon the pervasiveness of which has been stressed in his work, and the mechanisms by which flight is lost, including heterochrony and differential development. Feduccia has argued against the monophyly of the Ratitae, supporting instead independent derivation of ratite lineages, perhaps from flying ancestral paleognathous taxa, like the Lithornithiformes.
Feduccia is best known for his criticisms of the hypothesis, accepted by most paleontologists, that birds originated from and are deeply nested within Theropoda, and are therefore living theropod dinosaurs. Feduccia's first contribution relative to the origin and early evolution of birds, and their relationship with dinosaurs, was a critical review of the evidence then available for dinosaurian endothermy in 1973. In a 1979 paper, Feduccia and Tordoff argued, against the position taken by John Ostrom, that Archaeopteryx was capable of powered flight, as indicated by the asymmetrical vanes of its primary feathers, a feature found only in flying birds. In a paper coauthored with Storrs Olson in the same year, Feduccia noted that the robust furcula of Archaeopteryx could have served as a site of attachment for a well-developed M. pectoralis major, the principal depressor of the avian wing, responsible for powering the downstroke during avian flight. Olson and Feduccia concluded that this provided further evidence for the flight capability of Archaeopteryx. These initial excursions into the subject, and the argument that Archaeopteryx was clearly a bird, albeit primitive, were expanded upon in Feduccia's 1980 book, The Age of Birds. Feduccia here criticized the theropod hypothesis for the origin of birds, but his position was largely agnostic, conceding that there was evidence in support of both a theropod ancestry of birds and an ancestry from more basal archosaurs, perhaps similar in overall morphological organization to Euparkeria. Feduccia nevertheless suggested that on the basis of closer stratigraphic fit, ancestry from basal archosaurs rather than from coelurosaurian theropods might prove a better phylogenetic hypothesis. He thus, essentially, agreed with the model for the origin of birds proposed by Gerhard Heilmann in his influential 1926 book The Origin of Birds. Feduccia also criticized "ground-up" theories for the origin of avian flight, arguing on biophysical grounds that they were implausible, and noting that in other cases in which flight has developed among vertebrates it has occurred in an arboreal context. He argued, instead, for a "trees-down" model for the origin of avian flight due to its lack of the biophysical constraints hindering "ground-up" acquisition of flight and due to the ability to call upon biologically functional stages, represented by living analogues, at each stage in the evolution of flight.
Feduccia's skepticism about the origin of birds from theropods and a "ground-up" origin of avian flight, which in the absence of any evidence for small, arboreal theropods seemed a concomitant requirement of that hypothesis, increased following publication of The Age of Birds, culminating in a series of publications in the latter half of the 1980s and the early 1990s expanding upon arguments presented in The Age of Birds. In his 1985 contribution to the Eichstatt Archaeopteryx Conference, a major international meeting on the interpretation and significance of Archaeopteryx, as well as on the origin and early evolution of birds and avian flight, held in Eichstatt, Germany, Feduccia criticized hypotheses for the evolution of feathers in non-aerodynamic contexts in endothermic small theropod dinosaurs. He argued that these hypotheses failed to account for the elaborate aerodynamic architecture of the feather vane and rachis, and that thermoregulatory functions would have been adequately served by hair, which is a developmentally simpler structure. In a 1993 paper, Feduccia analyzed claw curvature arcs in the manual and pedal claws of Archaeopteryx and other birds, and found that Archaeopteryx clustered with other arboreal birds, suggesting that it was an arboreal animal rather than a terrestrial cursor or a bird which spent any considerable time on the ground, as is argued by some other workers.
In other publications in the early 1990s, Feduccia expanded on earlier arguments for the evolution of feathers in a primarily aerodynamic rather than thermoregulatory context. In 1996, Feduccia published the first edition (second edition in 1999) of The Origin and Evolution of Birds, a comprehensive review of his research on both early avian evolution and a synopsis of the history of the Tertiary radiation of modern birds. The book presented a thorough overview of earlier criticisms of the theropod hypothesis for the origin of birds and a "ground-up" origin of avian flight, expanded on many of those arguments, and presented a series of new arguments questioning the hypotheses of homology advanced as evidence for the theropod hypothesis. Feduccia argued that many of the proposed homologous similarities between theropods and birds were ambiguous, and that other similarities between birds and theropods could plausibly be explained as homoplasy, particularly those in the hindlimb and pelvis. Feduccia also focused upon the discrepancy between embryological evidence identifying the digits of the avian manus as the second, third, and fourth of the primitively pentadactyl archosaur manus, and paleontological evidence indicating that theropod dinosaurs primitively reduced their fourth and fifth manual digits, eventually retaining only the first, second, and third (with further reduction in some groups, like tyrannosaurs. This emerged as a principal argument in Feduccia's research on the origin of birds, and was the subject of developmental studies of the ostrich definitively identifying first and fifth digital condensations in the embryonic hand, confirming a pentadactyl ground state for the avian manus with symmetrical reduction, unlike the situation indicated by paleontological evidence for theropods. This conclusion has been supported by some other workers, but others have proposed various responses (see below, under Controversy).
In recent years, Feduccia has argued that the discovery of spectacular new fossils from the Cretaceous of China, like Microraptor, and other taxa with unambiguous feathers, like the oviraptorosaur Caudipteryx, suggest that there might have been an extensive, and hitherto unrecognized radiation of cryptic avian lineages, some of which rapidly lost flight and secondarily adopted a cursorial lifestyle, converging on theropods. On this argument, very birdlike groups like Dromaeosauridae and Oviraptorosauria, which are currently considered by most workers to be theropod dinosaurs, are thought actually to represent avian lineages, probably more derived than Archaeopteryx, that through homoplasy associated with the loss of flight and secondary acquisition of cursoriality, converged on theropod dinosaurs. Other lineages, like that represented by Microraptor and Anchiornis, are hypothesized to be have been flighted. This argument represents a shift from Feduccia's earlier position in the 1990s, as he acknowledged in a 2002 paper where he first endorsed this view. Feduccia has expanded upon this argument in subsequent papers.
Feduccia has appeared frequently on national TV and radio, including NPR, Voice of America, BBC, CNN, ABC (Australia), NHK (Japan) and MacNeil/Lehrer Report, and is a popular university lecturer. Feduccia served as Chair of the Department of Biology at Chapel Hill from 1997–2002, and prior to that was Chair of the Division of Natural Sciences. He is an elected Fellow of the American Ornithologists’ Union and the American Association for the Advancement of Science.
Feduccia's work has been unusually controversial, perhaps because of his skepticism about the theropod origin of birds, which is accepted by many biologists, and which has historically been a particularly divisive topic in vertebrate zoology. Feduccia's principal academic work, The Origin and Early Evolution of Birds, was well received by some workers, and was winner of the Association of American Publishers 1996 award for Excellence in Biology. However, it received very negative reviews from several paleontologists, primarily on account of the book's criticisms of the theropod hypothesis for the origin of birds. Feduccia has been criticized for failing to use cladistics in his studies of the origin and the evolution of birds, and this criticism has been related to further criticisms of, particularly, his arguments against the theropod origin of birds, as well as some of his hypotheses on the phylogeny of modern birds. In a 2002 paper in The Auk, the journal of the American Ornithologists' Union, Richard Prum presented a summary of the current state of the theropod hypothesis for the origin of birds, and urged its acceptance by and integration within ornithology. Feduccia responded with criticism of this view, arguing that the origin of birds was a complex and as yet unresolved problem to which the theropod hypothesis as presently formulated was a simplistic answer, ignoring contrary evidence. Prum responded to this paper and criticized Feduccia's failure to use cladistics and to specify an explicit alternative sister-group with which to ally birds. He particularly singled out Feduccia's adoption of the view that some theropod taxa are actually birds that have been mistaken for theropods through convergence associated with flight loss and secondary adoption of cursoriality. Prum argued, finally, that Feduccia's methodology and view of the origin and early evolution of birds are pseudoscientific.
Several of the arguments about whether similarities between birds and theropods are homologous that have been advanced by Feduccia have been particularly contentious. One example is identification of the digits of the avian and theropod hands, and whether, and if so by what mechanism, it might be possible to explain the discrepancy between the conflicting digital identities of tridactyl theropods and birds. Wagner and Gauthier proposed that a homeotic frame shift, whereby expression domains for groups of genes like the Hox d group, were repositioned during limb bud development, resulting in the development of the first, second, and third digits of the archosaur manus from what were originally condensations for the second, third, and fourth. This view has been supported by some other workers. Feduccia has responded to these counterarguments, and debate continues. Another response to Feduccia's digital homology argument is the counterargument that evidence from the transitional Limusaurus inextricabilis suggests that theropods too have the three digits II, III and IV.
- Library of Congress entry
- Feduccia (1980)
- Feduccia (1999)
- Ostrom, J. H. (1973). "The ancestry of birds". Nature 242 (5393): 136. Bibcode:1973Natur.242..136O. doi:10.1038/242136a0.
- Ostrom, J. H. (1976). "Archaeopteryx and the origin of birds". Biological Journal of the Linnean Society 8 (2): 91–182. doi:10.1111/j.1095-8312.1976.tb00244.x.
- Gauthier, J. A. (1986). "Saurischian monophyly and the Origin of Birds". In Padian, K. The Origin of Birds and the Evolution of Flight. Memoirs of the California Academy of Sciences 8. California Academy of Sciences. pp. 1–55. ISBN 0-940228-14-9.
- Padian, Kevin. (2004). "Basal Avialae". In Weishampel, David B.; Dodson, Peter; & Osmólska, Halszka (eds.). The Dinosauria (Second ed.). Berkeley: University of California Press. pp. 210–231. ISBN 0-520-24209-2.
- Feduccia, A. (1974). "Morphology of the bony stapes in New and Old World suboscines: new evidence for common ancestry" (PDF). Auk 91: 427–429. JSTOR 4084529.
- Feduccia, A. (1975). "Morphology of the bony stapes (columella) in the Passeriformes and related groups: evolutionary implications". University of Kansas Museum of Natural History Miscellaneous Publications 63: 1–34.
- Feduccia, A. (1975). "Morphology of the bony stapes in Menuridae and Acanthisittidae: evidence for oscine affinities" (PDF). Wilson Bulletin 87 (3): 418–420.
- Feduccia, A.; Ferree, C. E. (1978). "Morphology of the bony stapes (columella) in owls: evolutionary implications". Proceedings of the Biological Society of Washington 91: 431–438.
- Feduccia, A. (1977). "The whalebill is a stork". Nature 266 (5604): 719–720. Bibcode:1977Natur.266..719F. doi:10.1038/266719a0.
- Wetmore, A. (1926). "Fossil birds from the Green River deposits of eastern Utah". Annals of the Carnegie Museum 16: 391–402. ISSN 0097-4463.
- Olson, S. (1994). "A giant Presbyornis (Aves: Anseriformes) and other birds from the Paleocene Aquia Formation of Maryland and Virginia". Proceedings of the Biological Society of Washington 107: 429–435. hdl:10088/6493.
- Ericson, Per G. P. (1997). "Systematic position of the Paleogene family Presbyornithidae (Aves: Anseriformes)". Zoological Journal of the Linnean Society 121 (4): 429–483. doi:10.1111/j.1096-3642.1997.tb01286.x.
- Feduccia, A. (1977b). "Hypothetical stages in the evolution of modern ducks and flamingos". Journal of Theoretical Biology 67 (4): 715–721. doi:10.1016/0022-5193(77)90256-9. PMID 904341.
- Feduccia, A. (1978). "Presbyornis and the evolution of ducks and flamingos". American Scientist 66 (3): 298–304. Bibcode:1978AmSci..66..298F.
- Olson, S. L.; Feduccia, A. (1980). "Presbyornis and the origin of the Anseriformes (Aves: Charadriomorphae)". Smithsonian Contributions to Zoology 323 (323): 1–24. doi:10.5479/si.00810282.323.
- Cracraft, J. 1988. "The major clades of birds". Pages 339–361 in The Phylogeny and Classification of the Tetrapods, Volume I: Amphibians, Reptiles, Birds (ed. M. J. Benton). Clarendon Press: Oxford.
- Mindell, D. P., M. D. Sorenson, C. J. Huddleston, H. C. Miranda Jr., A. Knight, S. J. Sawchuk, and T. Yuri. 1997. Phylogenetic relationships among and within select avian orders based on mitochondrial DNA, pp. 213–247 in Avian Molecular Evolution and Systematics (ed. D. P. Mindell). Academic Press: San Diego.
- Livezey, B. C. (1997). "A phylogenetic analysis of basal Anseriformes, the fossil Presbyornis, and the interordinal relationships of waterfowl". Zoological Journal of the Linnean Society 121 (4): 361–428. doi:10.1111/j.1096-3642.1997.tb01285.x.
- Groth, J. G.; Barrowclough, G. F. (1999). "Basal divergences in birds and the phylogenetic utility of the nuclear RAG-1 gene". Molecular Phylogenetics and Evolution 12 (2): 115–123. doi:10.1006/mpev.1998.0603. PMID 10381315.
- Cracraft, J. and J. Clarke. 2001. The basal clades of modern birds, pp. 143–156 in New Perspectives on the Origin and Early Evolution of Birds: Proceedings of the International Symposium in Honor of John H. Ostrom (eds. J. Gauthier and L. F. Gall). Yale University Press: New Haven
- Mayr, G. (2004). "Morphological evidence for sister group relationship between flamingos (Aves: Phoenicopteridae) and grebes (Podicipedidae)". Zoological Journal of the Linnean Society 140 (2): 157–169. doi:10.1111/j.1096-3642.2003.00094.x.
- Feduccia, A.; McGrew, P. O. (1974). "A flamingolike wader from the Eocene of Wyoming". Contributions to Geology (University of Wyoming) 113 (2): 49–61.
- Feduccia, A. (1976). "Osteological evidence for shorebird affinities of the flamingos" (PDF). Auk 93: 587–601. JSTOR 4084959.
- Olson, S.; Feduccia, A. (1980). "Relationships and evolution of flamingos (Aves: Phoenicopteridae)". Smithsonian Contributions to Zoology 316 (316): 1–73. doi:10.5479/si.00810282.316. hdl:10088/5226.
- Feduccia (1999), p. 210
- Feduccia, A. (1995). "Explosive evolution in Tertiary birds and mammals". Science 267 (5198): 637–638. Bibcode:1995Sci...267..637F. doi:10.1126/science.267.5198.637. PMID 17745839.
- Feduccia, A. (2003). "Big Bang for Tertiary birds?" (PDF). Trends in Ecology and Evolution 18 (4): 172–176. doi:10.1016/S0169-5347(03)00017-X.
- Olson, S. L.; Parris, D. C. (1987). "The Cretaceous birds of New Jersey" (PDF). Smithsonian Contributions to Paleobiology 63 (63): 1–22. doi:10.5479/si.00810266.63.1.
- Feduccia, A. (1985). The morphological evidence for ratite monophyly: fact or fiction? Proceedings of the Eighteenth International Ornithological Congress, 184–190.
- Feduccia, A. (1973). "Dinosaurs as reptiles". Evolution 27 (1): 166–169. doi:10.2307/2407132. JSTOR 2407132.
- Feduccia, A.; Tordoff, H. B. (1979). "Feathers of Archaeopteryx: asymmetric vanes indicate aerodynamic function". Science 203 (4384): 1021–1022. Bibcode:1979Sci...203.1021F. doi:10.1126/science.203.4384.1021. PMID 17811125.
- Olson, S. L.; Feduccia, A. (1979). "Flight capability and the pectoral girdle of Archaeopteryx". Nature 278 (5701): 247–248. Bibcode:1979Natur.278..247O. doi:10.1038/278247a0. hdl:10088/6524.
- Feduccia (1980), p. 37
- Tudge, Colin. The Bird: A Natural History of Who Birds Are, Where They Came From, and How They Live. Three Rivers Press; Reprint edition. September 7, 2010. Page 58.
- Feduccia, A. 1985. On why the dinosaur lacked feathers, pp. 75–79 in The Beginnings of Birds: Proceedings of the International Archaeopteryx Conference Eichstatt 1984 (M. K. Hecht, J. H. Ostrom, G. Viohl, and P. Wellnhofer, eds.). Freunde des Jura-Museums Eichstatt: Eichstatt.
- Feduccia, A. (1993a). "Evidence from claw geometry indicating arboreal habits for Archaeopteryx". Science 259 (5096): 790–793. Bibcode:1993Sci...259..790F. doi:10.1126/science.259.5096.790. PMID 17809342.
- Elzanowski, A. 2002. Archaeopterygidae (Upper Jurassic of Germany), pp. 129–159 in Mesozoic Birds: Above the Heads of Dinosaurs (L. M. Chiappe and L. M. Witmer, eds.). University of California Press
- Mayr, G.; Pohl, B.; Hartman, S.; Peters, D. Stefan (2007). "The tenth skeletal specimen of Archaeopteryx". Zoological Journal of the Linnean Society 149: 97–116. doi:10.1111/j.1096-3642.2006.00245.x.
- Feduccia, A. (1993b). "Aerodynamic model for the early evolution of feathers provided by Propithecus (Primates, Lemuridae)". Journal of Theoretical Biology 160 (2): 159–164. doi:10.1006/jtbi.1993.1010.
- Feduccia, A. (1995). "The aerodynamic model for the evolution of feathers and feather misinterpretation". Courier Forschungsinstitut Senckenberg 181: 65–77.
- Burke, A. C.; Feduccia, A. (1997). "Developmental patterns and the identification of homologies in the avian hand". Science 278 (5338): 666–669. Bibcode:1997Sci...278..666B. doi:10.1126/science.278.5338.666.
- Feduccia, A.; Nowicki, J. (2002). "The hand of birds revealed by early ostrich embryos". Naturwissenschaften 89 (9): 391–393. Bibcode:2002NW.....89..391F. doi:10.1007/s00114-002-0350-y. PMID 12435089.
- Kundrát, Martin; Seichert, Václav; Russell, Anthony P.; Smetana, Karel (August 2002). "Pentadactyl pattern of the avian wing autopodium and pyramid reduction hypothesis" (PDF). Journal of Experimental Zoology 294 (2): 152–159. doi:10.1002/jez.10140. PMID 12210116.
- Galis, F.; Kundrat, M.; Sinervo, B. (2003). "An old controversy solved: bird embryos have five fingers". Trends in Ecology and Evolution 18: 7–9. doi:10.1016/S0169-5347(02)00018-6.
- Feduccia, A. (2002). "Birds are dinosaurs: simple answer to a complex problem". Auk 119 (4): 1187–1201. doi:10.1642/0004-8038(2002)119[1187:BADSAT]2.0.CO;2. JSTOR 4090252.
- Feduccia, A.; Lingham-Soliar, T.; Hinchliffe, J. R. (2005). "Do feathered dinosaurs exist? Testing the hypothesis on morphological and paleontological evidence". Journal of Morphology 266 (2): 125–166. doi:10.1002/jmor.10382. PMID 16217748.
- Feduccia, A.; Martin, L. D.; Tarsitano, S. (2007). "Archaeopteryx 2007: Quo vadis?". Auk 124 (2): 373–380. doi:10.1642/0004-8038(2007)124[373:PIOAQV]2.0.CO;2. JSTOR 25150288.
- Witmer, L. M. 1991. Perspectives on avian origins. Pages 427–466 in Origins of the Higher Groups of Tetrapods: Controversy and Consensus (eds. H.-P. Schultze and L. Trueb). Cornell University Press: Ithaca
- Witmer, L. M. 2002. The debate on avian ancestry: phylogeny, function, and fossils. Pages 3–30 in Mesozoic Birds: Above the Heads of Dinosaurs (eds. L. M. Chiappe and L. M. Witmer). University of California Press: Berkeley.
- Mayr, E. (1997). "Review of The Origin and Evolution of Birds by Alan Feduccia (Yale University Press, 1996)". American Zoologist 37: 210–211. JSTOR 3883960.
- Padian. "The Origin and Evolution of Birds by Alan Feduccia (Yale University Press, 1996)". American Scientist 85: 178–181.
- Norell, M. A.; Chiappe, L. M. (1997). "Flight from reason. Review of: The Origin and Evolution of Birds by Alan Feduccia (Yale University Press, 1996)". Nature 384 (6606): 230. Bibcode:1996Natur.384..230N. doi:10.1038/384230a0.
- Padian, K. 2001. "The false issues of bird origins: an historiographic perspective". Pages 485–499 in New Perspectives on the Origin and Early Evolution of Birds: Proceedings of the International Symposium in Honor of John H. Ostrom (eds. J. Gauthier and L. F. Gall). Yale University Press: New Haven.
- Makovicky, P. J., and G. J. Dyke. 2001. "Naive falsification and the origin of birds". Pages 501–509 in New Perspectives on the Origin and Early Evolution of Birds: Proceedings of the International Symposium in Honor of John H. Ostrom (eds. J. Gauthier and L. F. Gall). Yale University Press: New Haven.
- Prum, R. O. (2002). "Why ornithologists should care about the theropod origin of birds". Auk 119: 1–17. doi:10.1642/0004-8038(2002)119[0001:WOSCAT]2.0.CO;2.
- Prum, R. O (2003). "Are current critiques of the theropod origin of birds science? Rebuttal to Feduccia (2002)". Auk 120 (2): 550–561. doi:10.1642/0004-8038(2003)120[0550:ACCOTT]2.0.CO;2.
- Wagner, G.; Gauthier, J. A. (1999). "1,2,3=2,3,4: a solution to the problem of the homology of the digits in the avian hand". Proceedings of the National Academy of Sciences USA 96 (9): 5111–5116. Bibcode:1999PNAS...96.5111W. doi:10.1073/pnas.96.9.5111. PMC 21825. PMID 10220427.
- Vargas, A. O.; Fallon, J. F. (2005). "Birds have dinosaur wings: the molecular evidence". Journal of Experimental Zoology 304B (1): 85–89. doi:10.1002/jez.b.21023. PMID 15515040.
- Vargas, A. O.; Fallon, J. F. (2005). "The digits of the wings of birds are 1, 2, and 3. A review". Journal of Experimental Zoology 304B (3): 206–219. doi:10.1002/jez.b.21051. PMID 15880771.
- Xu, X.; Clark, J.M.; Mo, J.; Choiniere, J.; Forster, C.A.; Erickson, G.M.; Hone, D.W.E.; Sullivan, C. et al. (2009). "A Jurassic ceratosaur from China helps clarify avian digital homologies" (PDF). Nature 459 (18): 940–944. Bibcode:2009Natur.459..940X. doi:10.1038/nature08124. PMID 19536256.
- Feduccia, A. (1980). The Age of Birds (1st ed.). Cambridge: Harvard University Press. ISBN 0-674-00975-4.
- Feduccia, A. (1999). The Origin and Evolution of Birds (2nd ed.). New Haven: Yale University Press. ISBN 0-300-07861-7.