Thomas Henry Huxley and the reptile to bird transition

Abstract The overwhelming evidence that birds evolved from maniraptoran theropod dinosaurs has rekindled an interest in the work of the Victorian anatomist Thomas Henry Huxley. Many popular and technical accounts credit Huxley with being the first to propose that birds evolved from dinosaurs, but this is a misinterpretation of Huxley's work. During the 1860s Huxley was preoccupied with identifying the basic ‘groundplans’ that united vertebrate forms. Birds and reptiles were two groups united by a shared body plan, with dinosaurs representing an intermediate form. Huxley did not begin to cast dinosaurs as transitional forms between birds and earlier reptiles until he read Ernst Haeckel's Generelle Morphologie , at which time Huxley amassed ample anatomical evidence to illustrate how birds could have evolved from something dinosaur-like. Even then, however, Huxley did not say that birds had evolved from dinosaurs. As he explicitly stated in public addresses during the 1870s, small bird-like dinosaurs like Compsognathus only represented the form of what the true ancestors of birds might have looked like. Bird-like dinosaurs chiefly served to show that such a transition was possible. Thus, Huxley's views on the evolution of birds were much more complex than many modern authors appreciate.