I want to know the answer to the following question:
Who showed that extinct South American fossils were related to living species?
All the background I'm provided with is that "In March 1837, ornithologist John Gould announced that Darwin's rhea was a separate species from the previously described rhea (though their territories overlapped), that mockingbirds collected on the Galápagos Islands represented three separate species each unique to a particular island, and that several distinct birds from those islands were all classified as finches.". Is that enough to answer the question?
Answer: no