What are the advantages and limitations to using fossils to study the living things that lived in the past?

~Hello

Fossils are one of the best evidence of evolution, mainly because they are the remains of living organisms from the past, which allow us to compare them with living organisms. However, the fossil record is notoriously incomplete and it is also biased in favor of animals with hard body parts, such as skeletons and shells. Soft bodied organisms and soft body parts are rarely preserved and there are often huge gaps in some evolutionary sequences. For example, Archaeopteryx is the earliest known bird, but it is already a bird, nothwithstanding some of the features that are unquestionably reptilian. The earliest known reptile with feathers is Longisquama, but there is a gap of some 75 million years between Longisquama and Archaeopteryx, and nothing has yet been found that are intermediate between these two important fossils.

Finally, DNA is virtually unobtainable from fossils, making it nearly impossible to compare the DNA of most fossils with living organisms. In terms of phylogenetic tree construction, DNA data is far superior to fossil evidence. However, if not for the existence of fossils, DNA data alone would be unconvincing as evidence of evolutionary change.

~ Hope this could help