What is the Evolutionary History of Birds?
Birds are the third major evolutionary branch of sauropsids (reptiles), the first being non-archosaurian reptiles and the second being archosaurs (which includes dinosaurs and crocodiles). Birds are highly evolved archosaurs, and thus look nothing like their closest living relatives, the crocodilians. The evolutionary history of birds is long and complex, as they are the latest major branch of the sauropsid group. Previously, it was supposed that birds may have evolved from crocodilians or stem-group archosaurs in the early Mesozoic. Birds evolved from small dinosaurs around 155 million years ago, directly in the middle of the Mesozoic era. This is the scientific consensus, formed relatively recently — for many decades, the early evolutionary history of birds was unknown and a highly contentious topic. The notion that the evolutionary history of birds began with dinosaurs was proposed by a devotee of Darwin, Thomas Henry Huxley, shortly after the 1859 publication of The Origin of Speci
