KEY TO PLANTS ILLUSTRATED ON TIME CHART
1. Foerstia. These fossils may be the earliest known occurrence of bryophytes, although some authors have referred them to the brown algae. After Dawson.
2. Psilophyton. A primitive vascular plant. After Dawson.
3. Lepidodendron. After Hirmer.
4. Sigillaria. After Hirmer.
5. Calamites. After Hirmer.
6. Sphenophyllum. After Fuller and Tippo.
7. Equisetum. The only living genus of scouring rushes. After Fuller and Tippo.
8. Megaphyton. An ancient true fern. After Hirmer.
9. Modern tropical tree fern. After Fuller and Tippo.
10. Medullosa. An ancient seed fern. After Stewart.
11. Williamsonia. An extinct cycad-like tree. After Sahni.
12. Cycas. A modern cycad. After Chamberlain.
13. Baiera. A fossil leaf genus of ginkgo, whose only living representative is the species Ginkgo biloba, saved from extinction by careful cultivation in China. Several specimens of this “living fossil” were presented to this country by the Chinese and are now flourishing on many college campuses, including that of the University of Illinois. After Mägdefrau.
14. Cordaites. After Grand Eury.
15. Lebachia. A “transition conifer,” forerunner of present day conifers. After Mägdefrau.
16. Pinus. Modern pine. After Mägdefrau.
17. Acer. Common maple, an angiosperm whose leaves are also found among Tertiary fossils. After Mägdefrau.
18. Rosa. The prairie rose, an angiosperm.
19. Campsis. Trumpet vine, an angiosperm.
Geologic Time Chart
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
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.
At the beginning of the Pennsylvanian Period, Illinois was part of a vast lowland that stretched for hundreds of miles to the north, south, and west, and was bordered on the east by highlands. At times much of the plain was swampy and, because the climate was relatively warm and moist, great jungles of fast growing trees, shrubs, and vines covered the landscape. As successive generations of plants lived and died, plant material fell into the swamp waters and, protected there from decay, accumulated.
Frequently during the period, seas spread over the swampy lowlands, submerging the forests and covering them with mud. Each submergence lasted only a short time, geologically speaking. When the seas withdrew, the deposits of sand and mud left behind were cut by streams that carried fresh sand and mud from the eastern highlands. The streams eventually became clogged with sediments and when the lowland was again depressed swamp conditions returned and forests grew afresh. Such a cycle of deposition was repeated again and again during Pennsylvanian time, and after burial each layer of plant material gradually lost most of its liquids and gases and was slowly converted into one of the numerous coal beds presently found in Illinois.
Reconstruction of Pennsylvanian Coal-forming Swamp
In some places in the state conditions existed that were especially favorable for preservation of plants, and there delicately preserved fossils are found in great numbers. In the most favorable areas, such as in northern Illinois, the plants are preserved in stony nodules called concretions, but they also may be found separately as molds, casts, or petrifactions.
Molds (concave surfaces) and casts (convex surfaces) are fossilization phenomena in which the actual plant, embedded in the surrounding background rock, was dissolved, leaving a hollow space (mold) that subsequently filled with other material. A cast was thus formed that preserved the plant’s external features.
Most petrifactions are fossils in which silica, carbonate, or other material permeated or replaced the internal structures of the plant and preserved them so well that in most specimens the finest cellular details can be observed. Compressions, another kind of petrifaction, are the pressed carbonized remains of the plant itself.