The answer is homologous structures.
Homologous structures are structures that occur in different species but are similar enough to suggest that the species had a common ancestor. Simply, they re similar structures shared by different species. For example, amphibians, lizards, and mammals are separated into different classes but they have the similar anatomy of the front limbs. This supports the idea that these groups have a common ancestor but are not that similar to be in the same class.
