Perhaps two of the most important groups of fossils are the prokaryotes and protists, both single-celled organisms. They are not spectacular fossils and so may be less interesting to students than the more complicated metazoans and metaphytes, yet these two groups not only dominate life on Earth today, but they contribute enormously to our understanding of Earth and life history. Prokaryotes dominated the fossil record of Earth from 3.5 to nearly .5 billion years ago (Knoll, 1985). For the last 1.5 billion years, protists have been an important element in marine and probably other ecosystems.