Fossils are remains or impressions of past organisms that are found in the rocks. Fossils of lower strata belong to early periods while those of upper strata are of later periods. Arranging the fossils stratum wise will indicate the occurrence of different forms of life at different times. It is found that the early fossils generally belong to simple organisms. Complexity and elaboration increased gradually with evolution.
(i) Fossils indicate the path of evolution of different groups.
(ii) They can indicate the phylogeny of some organisms. e.g. horse, elephants.
(iii) Some fossils have characteristics intermediate between two groups e.g. Toothed bird Archaeopteryx.
They indicate how one group has evolved from another.
