According to many scientists, birds are essentially modified dinosaurs with feathers. American paleontologists Robert T. Bakker (1945–) and John H. Ostrom (1928–2005) did extensive research on the relationship between birds and dinosaurs in the 1970s. They suggested that the bony structure of small dinosaurs was very similar to Archaeopteryx, the first animal classified as a bird (it had true feathers)—thus dinosaurs and birds probably evolved from the same ancestors. Ostrom also suggested that dinosaurs may have been warm-blooded and thus more active and similar to birds. The evidence since that time has become stronger, as paleontologists continue to discover more dinosaur fossils—some that show even more evidence of birdlike feathers. In fact, in 2013, several researchers found yet another dinosaur fossil with evidence of feathers and suggested that dinosaurs were not “overgrown lizards,” but that feathered dinosaurs were actually the norm.