Similar gill pouches in embryos of a chick, human, and cat are an example of

This is an example of developmental homology. Studying embryological development of living things provides clues to the evolution of present-day organisms. During some stages of development, organisms exhibit ancestral features in whole or incomplete form. Homologous structures are those structures whose underlying similarity arises from their being derived from a common ancestral origin while analogous structure are those whose similarity comes from their performing of a similar function.

They both determine the exact age of rocks.