Final answer:
Modern birds evolved from a group of bipedal dinosaurs known as theropods. This is supported by evidence such as fossil records, including the Archaeopteryx, which exhibit both dinosaur and avian features.
Step-by-step explanation:
The group of reptiles that gave rise to modern birds is known as the theropods. Overwhelming evidence from paleontology supports the evolution of birds from this clade of dinosaurs. Theropods belong to the saurischian, or "lizard-hipped", lineage of dinosaurs, not the ornithischian, or "bird-hipped", lineage, despite the latter's misleading name. The theropod dinosaurs include well-known species like the Deinonychus and the Archaeopteryx, the latter being one of the oldest known fossils linking dinosaurs and birds and providing significant evidence for their evolutionary relationship. Characteristics such as the structure of hip and wrist bones, the presence of the wishbone, and adaptations for possibly endothermic metabolisms are some of the shared traits that highlight the evolutionary link between theropod dinosaurs and modern birds.