Heilmann's extremely thorough approach ensured that his book became a classic in the field and its conclusions on bird origins, as with most other topics, were accepted by nearly all evolutionary biologists for the next four decades, despite the discovery of clavicles in the primitive theropod Segisaurus in 1936.
Heilmanns meget grundige fremgangsmåde sikrede at hans bog blev en klassiker indenfor feltet og dens konklusioner om fuglenes oprindelse, som med de fleste andre emner, blev accepteret af næsten alle evolutionære biologer i de næste fire årtier, på trods af opdagelsen af claviculae hos den primitive theropod Segisaurus i 1936.