Archaeornithes

The term Archaeornithes refers to a subclass of fossil birds that represent the earliest and most primitive forms. These ancient birds retained distinct reptilian characteristics. This subclass includes the genera Archaeornis and Archaeopteryx.1

Fossils such as Archaeopteryx, dating back to the late Jurassic Period (approximately 150 million years ago), exhibit a mix of reptilian and avian features. While possessing feathers and some skeletal traits indicating an intermediate stage between reptiles and modern birds, Archaeopteryx also had teeth in its jaws and claws on its digits, suggesting it may have glided rather than flown. The discovery of other feathered dinosaurs, like Sinosauropteryx from the Cretaceous Period, further supports the evolutionary link between dinosaurs and birds, with some of these dinosaurs possessing feather-like structures before birds evolved.23