Britannica Sources used in this answer

When did the earliest birds appear in the fossil record?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Jurassic paleogeography — Jurassic Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Jurassic Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

The earliest birds are widely considered to have evolved from small theropod dinosaurs during the Jurassic Period.12

For many years, the genus Archaeopteryx, which dates to approximately 150 million years ago during the Late Jurassic, was regarded as the oldest known fossil bird. However, the classification of Archaeopteryx as the most primitive bird has been challenged by the discovery of other birdlike fossils from the same era or earlier, such as Xiaotingia zhengi and Aurornis xui, which are estimated to have lived roughly 5 to 10 million years before Archaeopteryx.34

Because these discoveries share many features once considered diagnostic of birds—such as feathers, wishbones, and three-fingered hands—some paleontologists now classify Archaeopteryx as a dinosaur rather than a bird. Consequently, the precise point in the fossil record where the first true bird appears remains a subject of ongoing scientific debate, as the single ancestor from which all modern bird lineages originate has yet to be definitively identified.431