_Time Units_ _Era and Years_ CENOZOIC “Recent Life” Pleistocene Pliocene Miocene Oligocene Eocene Paleocene MESOZOIC “Middle Life” Cretaceous 70 million herbaceous lycopods Jurassic 25 million yellow-green algae selaginellids Triassic 30 million cycad-like plants Equisetum PALEOZOIC “Ancient Life” Permian 25 million transition conifers pines, spruces, firs, etc. Equisetites Pennsylvanian 25 million ferns related to modern families bryophytes Mississippian 30 million seed ferns calamites cycads Devonian 55 million cordaites sphenophyllids ancient ferns Silurian 40 million psitopsids Foerstia Ordovician 80 million red algae green algae Cambrian 80 million PROTEROZOIC _and_ ARCHAEOZOIC ERAS 4½ billion years blue-green algae chemosynthetic bacteria? NO CERTAIN FOSSILS KNOWN _Plants_ Algae yellow-green algae brown algae red algae green algae blue-green algae Mosses bryophytes Foerstia Vascular Plants “Whisk Ferns” psitopsids Club-mosses scale and seal trees quillworts herbaceous lycopods Scouring Rushes, Horsetails Equisetites Equisetum calamites selaginellids Ferns and Seed Plants Ferns ancient ferns ferns related to modern families Gymnosperms Cycads seed ferns cycads cycad-like plants Ginkgo Conifers cordaites transition conifers pines, spruces, firs, etc. Flowering Plants _Field Book_ PENNSYLVANIAN PLANT FOSSILS OF ILLINOIS Charles Collinson and Romayne Skartvedt [Illustration: Illuminated P] Plants that flourished 200 million years ago have made Illinois one of the best known fossil collecting sites in the world. The unusual abundance and preservation of these fossils in the northern part of the state have brought collectors to Illinois from many countries, and prized specimens from that area may be seen in science museums throughout the world. The remarkable fossils represent plants that lived during the geologic period called the Pennsylvanian or Coal Age and are the result of special geologic conditions that occurred repeatedly during the period.