Dinosaurs and The Origin of Birds

Abstract

The evolutionary relationships of birds have been debated ever since the discovery of a fossil bird, Archaeopteryx , in 1861, that has bird‐like feathers but reptilian teeth and a long bony tail. Recent discoveries of feathered dinosaurs have confirmed analyses of bird relationships beginning in the 1970s that placed Archaeopteryx and birds within one group of dinosaurs, the Theropoda. Recognition of this relationship and discovery of a variety of new species have allowed evolutionary biologists to study for the first time many aspects of the transition from ground‐living theropods to flying birds. Many new details about the evolution of feathers, reproductive features of birds and flight have emerged from these fossils and continue to emerge as new fossils are found. The precise relationships of birds to theropods is still debated, but the scansoriopterygids, dromaeosaurs and troodontids are amongst the closest relatives of birds. Key Concepts: The closest living relatives of birds are the crocodilians and together they form the group Archosauria. The origins of birds lie with fossil archosaurs, which include dinosaurs, the flying reptiles called pterosaurs and the many fossil relatives of crocodilians. Evolutionary relationships are studied using cladistic analysis of similarities shared amongst different species. Cladistic analyses strongly support birds being closely related to a subgroup within the theropod dinosaurs called Coelurosauria and especially with the scansoriopterygid, dromaeosaur and troodontid coelurosaurs. Fossil coelurosaurs with feathers from China provide convincing evidence that birds are coelurosaurs, and that during the course of evolution feathers arose before flight.