Traces and preserved remnants of dead animals and plants are called fossils. The study of fossils is called paleontology.
An embryo is defined as a multicellular structure that is developed from the zygote and gives rise to new offspring generally present inside the female tissue or egg-membrane.
Those organs which are present as reduced structures and are function less in the body are called vestigial organs.
Homologous organs are those organs which have a similar embryonic origin and basic plan but different function.