<P> The scientific question within which larger group of animals birds evolved, has traditionally been called the origin of birds . The present scientific consensus is that birds are a group of theropod dinosaurs that originated during the Mesozoic Era . </P> <P> A close relationship between birds and dinosaurs was first proposed in the nineteenth century after the discovery of the primitive bird Archaeopteryx in Germany . Birds share many unique skeletal features with dinosaurs . Moreover, fossils of more than twenty species of dinosaur have been collected with preserved feathers . There are even very small dinosaurs, such as Microraptor and Anchiornis, which have long, vaned, arm and leg feathers forming wings . The Jurassic basal avialan Pedopenna also shows these long foot feathers . Witmer in 2009 concluded that this evidence is sufficient to demonstrate that avian evolution went through a four - winged stage . Fossil evidence also demonstrates that birds and dinosaurs shared features such as hollow, pneumatized bones, gastroliths in the digestive system, nest - building and brooding behaviors . </P>

Who are believed to be the direct ancestors to birds