they're still birds. they're still finches. it's not like they turned into a giraffe.
This is the kind of change that can happen in tens of thousands of years, they are in the same general group of finches, but they have become a new species. This proves the concept. There are no barriers to further change. You would have to explain why they cannot change even further. How much different do they have to be from an original species? Into penguins? Are they different enough for you? How about a land animal into whales? Because there is evidence for that too.
i did acknowledge it, and the subsequent stasis, and said that there has been no fossil evidence of this tree of life that darwin suggests exists in relation to it and it's ancestry.
Actually, you could not be more wrong- all fossil evidence supports the tree of life.