What are dinosaurs' closest living relatives?

Until quite recently the answer to this question would have been crocodiles. However recent research, mainly by Professor John Ostrom of Yale University, has shown that there is a very close relationship between the earliest known bird Archaeopteryx from the Upper Jurassic of Bavaria and some small predatory dinosaurs such as Troondon. The similarities between these two creatures leads us to believe that birds are the living descendants of small predatory dinosaurs, and therefore that the nearest living relatives of some dinosaurs are birds.