Origin of birds The origin of birds has historically been a
contentious topic within evolutionary biology. However, most
researchers now support the view that 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. Birds share many unique skeletal
features with dinosaurs. Moreover, fossils of more than twenty
species of dinosaur have been collected which preserve 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 (2009) has 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 t