 His work, originally written in Danish as "Vor Nuvaerende Viden om Fuglenes Afstamning", was compiled, translated into English, and published in 1926 as "The Origin of Birds".Like Huxley, Heilmann compared "Archaeopteryx" and other birds to an exhaustive list of prehistoric reptiles, and also came to the conclusion that theropod dinosaurs like "Compsognathus" were the most similar.However, Heilmann noted that birds had clavicles (collar bones) fused to form a bone called the furcula ("wishbone"), and while clavicles were known in more primitive reptiles, they had not yet been recognized in dinosaurs.