I spent most of my childhood with books about dinosaurs that played up the ancient beasties as overgrown lizards. The connection between dinosaurs and birds, while kind of flipping obvious once somebody points it out, was not much discussed among laypeople until I was in my teens. (That would be the 1990s, FYI.)
But, among scientists, the idea of a dinosaur-bird relationship is nothing new. In fact, Thomas Henry Huxley was making that connection back in the 1860s. On the Dinosaur Tracking blog, Brian Switek tells the fascinating story of how Huxley started to realize that dinosaurs and birds were related—a discovery that's all the more impressive because he figured it out without the help of some of the key transitional fossils we have access to today.
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Huxley did not suggest that birds were the direct descendants of dinosaurs. So much geologic time was unaccounted for, and so few dinosaurs were known, that Huxley could not point to any known fossil creature as the forerunner of birds. Instead he made his argument on anatomical grounds and removed the issue of time. Dinosaurs were proxies for what the actual bird ancestor would have been like, and flightless birds (such as the ostrich and emu) stood in for what Huxley thought was the most archaic bird type. (We now know that Huxley got this backwards—the earliest birds could fly, and flightless birds represent a secondary loss of that ability.) As Huxley went about collecting evidence for his case, though, he also gave dinosaurs an overhaul.