On the animals which are most nearly intermediate between birds and reptiles.

Huxley proposed a close relationship between birds and dinosaurs after the discovery in Germany of the primitive fossil bird Archaeopteryx. He made detailed comparisons of Archaeopteryx with various prehistoric reptiles and found that it was most similar to dinosaurs like Hypsilophodon and Compsognathus. Digital facsimile from the Biodiversity Heritage Library at this link.