How can you explain the degree of similarity between fossilized objects and modern organisms?

How can you explain the degree of similarity between fossilized objects and modern organisms? How can you explain the degree of difference between fossilized objects and modern organisms?

Some fossilized organisms closely resemble modern animals and plants. But there are also differences between modern animals and their ancestors. Everything is connected with the long evolution of the living. The differences are associated with the development of living organisms and adaptations to the environment. They got new organs, body parts and so on. But some organisms have barely changed in hundreds of millions of years. This is clearly seen in the examples of ferns. Fossilized traces of ferns on coals are the same as modern fern species.