Alan Feduccia

 ( American Ornithologists ) 

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.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. 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.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 In 1994, Feduccia argued that there was a "temporal paradox" due to most bird-like dinosaurs being known from the Cretaceous, while birds are thought to have originated in the Jurassic.

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 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 Cenozoic 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.

From 2002, 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. According to 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 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 and in his book Riddle of the Feathered Dragons.

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 hand, 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. Another response to Feduccia's digital homology argument is the counterargument that evidence from the transitional Limusaurus suggests that theropods too have the three digits II, III and IV.

Feduccia's model for the origin of most orders of modern birds in an explosive adaptive radiation after the end-Cretaceous extinction event is in conflict with some molecular evidence suggesting a deep Mesozoic origin for these taxa.Brown, J. W., and M. Van Tuinen. 2011. Evolving perceptions of the antiquity of the modern avian tree. Pages 306—324 in Living Dinosaurs: The Evolutionary History of Modern Birds (eds. G. Dyke and G. Kaiser). Wiley-Blackwell: Chichester.Lindlow, B. E. K. 2011. Bird evolution across the K-Pg boundary and the basal neornithine diversification. Pages 338—354 in Living Dinosaurs: The Evolutionary History of Modern Birds (eds. G. Dyke and G. Kaiser). Wiley-Blackwell: Chichester. It has also been argued that there is fossil evidence for the existence of multiple orders of modern birds from the Late Cretaceous,Hope, S. 2002. The Mesozoic radiation of Neornithes. Pages 339—388 in Mesozoic Birds: Above the Heads of Dinosaurs (eds. L. M. Chiappe and L. M. Witmer). University of California Press: Berkeley. but much of this material is fragmentary and interpretation is difficult. On the other hand, there do appear to be definitive exemplars of Anseriformes from the Late Cretaceous of Antarctica and Asteriornis from the latest Cretaceous of Belgium appears to be a Galliformes-Anseriformes mosaic; whether these finds refute the hypothesis that the principal adaptive radiation of modern birds occurred only after the end-Cretaceous extinction event is not clear, since the hypothesis is consistent with a limited adaptive radiation of neornithines in the Late Cretaceous. Sankar Chatterjee argues that the avian status of the controversial taxon Protoavis supports a deep Mesozoic origin of modern birds,