The First Of The True Birds
55, 000, 000 years ago the evolutionary march was marked by the sudden appearance of the first of the true birds, a small pigeonlike creature which was the ancestor of all bird life. This was the third type of flying creature to appear on earth, and it sprang directly from the reptilian group, not from the contemporary flying dinosaurs nor from the earlier types of toothed land birds. And so this becomes known as the age of birds as well as the declining age of reptiles.
~ The Urantia Book, (60:3.22)