What other chordate are birds most closely related to?

Birds are most closely related to crocodilians, which include crocodiles, alligators, and caimans. Birds and crocodilians are both reptiles, and they share many similarities in their anatomy and physiology. For example, both birds and crocodilians have scales, lay eggs, and have cold-blooded metabolisms. However, birds also have some unique characteristics, such as feathers and wings.