Scientists have been arguing about who was the ancestor of birds for a long time  There are mainly three theories about the origin of birds: the origin of slotted teeth, the origin of dinosaurs and the sister group of crocodiles, among which the origin of slotted teeth and the origin of dinosaurs have been hotly debated recently
The original bird found in North America was tens of millions of years earlier than Sinosauropteryx and Archaeopteryx. If the original bird was indeed a bird, the bird appeared almost at the same time as the dinosaur.
 The newly discovered fossils in recent years, especially a series of fossils found in western Liaoning, China, have once again stirred up the debate about the origin of birds, proving that birds are really descendants of dinosaurs