Final answer:
Birds descended from theropod dinosaurs, with the Deinonychus being a likely ancestor. The Archaeopteryx fossil provides key evidence of this evolutionary relationship. Modern birds evolved from these bipedal carnivores, not from the 'bird-hipped' dinosaurs.
Step-by-step explanation:
Birds are believed to have evolved from theropod dinosaurs, specifically from a group known as maniraptorans, which includes dinosaurs like the Deinonychus. This notion is supported by numerous paleontological findings, among which the most iconic is the fossil of Archaeopteryx, dating back to the Jurassic period and showcasing characteristics of both dinosaurs and birds.
While the evolution of flight remains a topic of ongoing research, the consensus is clear that modern birds are descendants of bipedal, carnivorous dinosaurs, even though they share a name with the 'birdhipped' Ornithischia, which are not their direct ancestors.