Scientists are still debating this question. Many researchers have suggested, based on fossils—and cladistic analysis—that modern birds arose around 60 million years ago. But more recent fossil discoveries have caused the debate to become heated, and some researchers suggest modern birds may have evolved more than 100 million years ago. The problem comes with how scientists look at bird evolution: some use the fossil records and others use genetic data, both of which yield conflicting results. New techniques, such as DNA sequencing, may help scientists resolve when and how the world’s close to 10,000 bird species originated.