Darwin failed to appreciate that the most divergent species of his finches, the Warbler Finch, was in fact more closely related to the others than to superficially similar species on the mainland.

The Warbler Finch became a bone of contention between Darwin and Gould.   Recall that Gould correctly recognized that the insectivorous Warbler Finch, which had a thin beak much like a warbler's rather than a thick one like a finch's, was in fact closely related phylogenetically to the other Darwin's finches.

Darwin did not accept this conclusion at the time the "Zoology of the voyage of H.M.S. Beagle" was published.   He added to the report (after John Gould had left for Australia),

"Although Mr. Gould confidently believes [that Certhidea, the Warbler Finch, is closely related to the other Galapagos finches], it has so much the appearance of a member of the Sylviadae [the large phylogenetic family of Old World warblers], he would by no means insist upon the above view . . . until the matter shall have been more fully investigated".

Since then anatomical, biochemical, and molecular studies have all confirmed Gould's conclusion.

So Gould was correct in recognizing the common ancestry of Darwin's finches despite divergent ecological specializations (what we would now call adaptive radiation of Darwin's finches).

Nevertheless, when he later catalogued the birds of Australia, Gould failed to recognize adaptive radiation there!

As author of the first classification of Australian birds, Gould presented most Australian families of birds as relatives of different Eurasian families.   In other words, the warbler-like birds in Australia were related to warblers of Eurasia -- not to superficially dissimilar birds in Australia.   His precedent was followed for over a hundred years by subsequent generations of ornithologists.

Only in the 1980's did ornithologists acknowledge that most of these Australian families had in fact radiated from one (or a few) ancestors that had colonized Australia from Eurasia some 10 MYA (million years ago).   Molecular evidence was conclusive, but once it became available ornithologists realized that the anatomical evidence was also conclusive -- it had just not been acknowledged.

So Gould was perceptive in recognizing adaptive radiation in Darwin's finches but he completely missed the grandest example of adaptive radiation in birds now known -- the adaptive radiation of hundreds of species of birds in Australia!