Similarity in traits can occur in two ways. Both species might have acquired the trait by descent from a common ancestor. In this case the structures are homologous. An example is the tetrapod limb, which has been inherited from early tetrapods in the late Devonian/early Carboniferous, about 360 million years ago. On the other hand, both might be independent adaptations to similar conditions in their habitat. In this case the structures are analogous. Convergent evolution leads to analogous features.