List of transitional fossils
This is a partial list of transitional fossils (fossil remains of groups that exhibit both "primitive" and derived traits). The fossils are listed in series, showing the transition from one group to another, representing significant steps in the evolution of major features in various lineages. These changes often represent major changes in morphology and anatomy, related to mode of life, like the acquisition of feathered wings for an aerial lifestyle in birds, or limbs in the fish/tetrapod transition onto land. Darwin noted that transitional forms could be considered common ancestors, direct ancestors or collateral ancestors  of living or extinct groups, but believed that finding actual common or direct ancestors linking different groups was unlikely. Collateral ancestors are relatives like cousins in genealogies in which they are not in your direct line of descent but do share a common ancestor (in this case it is a grandparent). This kind of thinking can be extended to groups of life. For instance, the well-known "Archaeopteryx" is a transitional form between non-avian dinosaurs and birds, but it is not the most recent common ancestor of all birds nor is it a direct ancestor of any species of  bird alive today. Rather, it is considered an extinct close evolutionary "cousin" to the direct ancestors. This may not always be the case, though, as some fossil species are proposed to be directly ancestral to others, like how "Australopithecus anamensis" is most likely to be ancestral to "Australopithecus afarensis". Human evolution. List of human evolution fossils