Birds are essentially modified dinosaurs with feathers. Robert T. Bakker (1945–) and John H. Ostrom (1928–2005) did extensive research on the relationship between birds and dinosaurs in the 1970s and concluded that the bony structure of small dinosaurs was very similar to Archaeopteryx, the first animal classified as a bird, but that dinosaur fossils showed no evidence of feathers. They proposed that birds and dinosaurs evolved from the same source.