In the 1960s, he showed that dinosaurs are more like big non-flying birds than they are like lizards (or "saurians"). Thomas Henry Huxley in the 1860s had thought birds evolved from dinosaurs, based on a comparison of "Archaeopteryx" with "Compsognathus". Huxley's idea was later discarded, mainly because Heilmann, in 1926, had different views.