What evidence connects birds to theropod dinosaurs?

Scientific evidence confirms that modern birds are living dinosaurs that evolved from a lineage of theropod dinosaurs over 150 million years ago.12

The connection is supported by numerous shared anatomical features and fossil discoveries:

• Feathers: Many nonavian theropods, such as Sinosauropteryx and Caudipteryx, possessed filamentous structures or true feathers. This indicates that feathers originally evolved for insulation, display, or camouflage rather than flight.13
• Skeletal Anatomy: Birds and theropods share hollow, thin-walled bones, a wishbone, air sacs, and a similar pelvis structure.43
• Wrist and Limb Structure: Theropods possess a unique wrist joint that allows the hand to flex sideways, a motion nearly identical to that used by birds in flight. Additionally, birds inherited their digitigrade foot structure—with three forward-facing toes—directly from these dinosaurs.32
• Transitional Fossils: Specimens like Archaeopteryx exhibit a mix of avian and dinosaurian traits, such as wings and feathers combined with teeth and a long, bony tail.43