Fossil Gaps 1i -- steve's forum

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i. �The [evolutionary] origin of birds is largely a matter of deduction. There is no fossil evidence of the stages through which the remarkable change from reptile to bird was achieved.� W. E. Swinton, �The Origin of Birds,� Biology and Comparative Physiology of Birds, editor A. J. Marshall (New York: Academic Press, 1960), Vol. 1, Chapter 1, p. 1.

Some have claimed birds evolved from a two-legged dinosaur known as a theropod. However, several problems exist.

A theropod dinosaur fossil found in China showed a lung mechanism completely incompatible with that of birds. [See John A. Ruben et al., �Lung Structure and Ventilation in Theropod Dinosaurs and Early Birds,� Science, Vol. 278, 14 November 1997, pp. 1267�1270.] In that report, �Ruben argues that a transition from a crocodilian to a bird lung would be impossible, because the transitional animal would have a life-threatening hernia or hole in its diaphragm.� [Ann Gibbons, �Lung Fossils Suggest Dinos Breathed in Cold Blood,� Science, Vol. 278, 14 November 1997, p. 1230.]

Bird and theropod �hands� differ. Theropods have �fingers� I, II, and III (having lost the �ring finger� and little finger), while birds have fingers II, III, and IV. �The developmental evidence of homology is problematic for the hypothesized theropod origin of birds.� [Ann C. Burke and Alan Feduccia, �Developmental Patterns and the Identification of Homologies in the Avian Hand,� Science, Vol. 278, 24 October 1997, pp. 666�668.] �...this important developmental evidence that birds have a II-III-IV digital formula, unlike the dinosaur I-II-III, is the most important barrier to belief in the dinosaur origin [for birds] orthodoxy.� [Richard Hinchliffe, �The Forward March of the Bird-Dinosaurs Halted?� Science, Vol. 278, 24 October 1997, p. 597.]