Origin of birds

The origin of birds has been a contentious topic within evolutionary biology for many years, but more recently a scientific consensus has emerged which holds that, in the phylogenetic sense, birds are a group of theropod dinosaurs that evolved during the Mesozoic Era. A close relationship between birds and dinosaurs was first proposed in the nineteenth century after the discovery of the primitive bird Archaeopteryx in Germany and has been all but confirmed since the 1960s by comparative anatomy and the cladistic method of analyzing evolutionary relationships. The ongoing discovery of feathered dinosaur fossils in the Liaoning Province of China has shed new light on the subject for both specialists and the general public.

Birds share hundreds of unique skeletal features with dinosaurs, especially with derived maniraptoran theropods like the dromaeosaurids, which most analyses show to be their closest relatives. Although harder to identify in the fossil record, similarities in the digestive and cardiovascular systems, as well as behavioral similarities and the shared presence of feathers, also link birds with dinosaurs. The ground-breaking discovery of fossilized Tyrannosaurus rex soft tissue allowed comparison of cellular anatomy and protein sequencing of collagen tissue, both of which provided additional evidence corroborating the dinosaur-bird relationship.

Only a few scientists still debate the dinosaurian origin of birds, suggesting descent from other types of archosaurian reptiles. Even among those who support dinosaurian ancestry, the exact phylogenetic position of early birds within theropods remains controversial. The origin of bird flight is a separate but related question for which there are also several proposed answers.