Final answer:
The two species of birds that evolved from a common ancestor belong to the same subclass called aves, part of the larger group archosaurs. Fossil evidence like Archaeopteryx and modern DNA analysis support this, showing both convergent and divergent evolution in bird species.
Step-by-step explanation:
DNA analysis revealing that two species of birds evolved from a common ancestor indicates that these two species belong to the same group called archosaurs, specifically the subclass aves, which contains all modern birds.
An example of this evolutionary relationship is the fossil of Archaeopteryx, which shares characteristics with both reptiles and birds, supporting the idea that birds evolved from theropod dinosaurs. Over time, birds have diversified into various clades such as the Paleognathae, Galloanserae, and Neoaves based on molecular analysis. This diversification shows both the convergent and divergent evolution as species adapted to different environments or ecological niches.
For instance, the emu in Australia and the ostrich in Africa, despite looking similar as flightless birds, actually share a closer genetic homology with other flying birds in their respective regions than with each other. This suggests that these species underwent convergent evolution due to similar selection pressures, but they are not closely related. Conversely, the discovery of various genera of birds with different traits on an island indicates divergent evolution as they have adapted to different niches within the same environment.