Only a fraction of the species that have ever lived are preserved in even one fossil. Of the fossils that do exist, most are of shellfish that lived in shallow seas. Animals with soft bodies such as worms and animals that live on land are very rarely found as fossils. Another problem is that we usually have only the hard parts to tell us what the animal was like. So we can only guess what colour it was, whether it had fur or not and if it had large ears.
Ammonite shells are among the most common fossils.
Like squids, ammonites had long tentacles. They are now extinct, but thrived in warm seas from 64 to 190 million years ago. Fish were the first creatures to have backbones, over 400 million years ago. The Devonian period from 408 to 360 million years ago is some-times called the Age of Fish. In a plant, there are no hard parts like shell and bone to be fossilized.