557 IL6ed no. 6 %e/M 6 Field Book PENNSYLVANIAN PLANT FOSSILS OF ILLINOIS Charles Collinson Romayne Skartvedt yilm&ti, State, Qecdaaicai S>4Mw&f STATE of ILLINOIS William G. Stratton, Governor DEPARTMENT of REGISTRATION and EDUCATION Vera M. Binks, Director 1960 ILLINOIS STATE GEOLOGICAL SURVEY John C. Frye, Chief URBANA, ILLINOIS 2 PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS Field Book PENNSYLVANIAN PLANT FOSSILS OF ILLINOIS Charles Collinson Romayne Skartvedt yiU4£i&tio*id> by McvUe, £. lUieA&n, Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/fieldbookpennsyl06coll FOREWORD HIS FIELD BOOK is intended to guide be- ginners in their collection and general classification of plant fossils. It illus- trates the plant fossils most commonly found in Illinois and relates them to the plants of which they were a part. A list of publications that will furnish more detailed identification of specimens is included. The book has been prepared in response to numerous in- quiries to the Illinois State Geological Survey from amateur collectors. Information has been drawn from numerous sources. The works of Hirmer, Janssen, Les- quereux, Noe, and Langford have been particular- ly useful. We are especially indebted to Dr. Robert M. Kosanke, paleobotanist at the Illinois State Geological Survey, and Dr. Wilson N. Stewart, professor of botany of the University of Illinois, for helpful suggestions and use of their libraries. [ 3 ] KEY TO PLANTS ILLUSTRATED ON TIME CHART 1. Foerstia. These fossils may be the earliest known oc- currence 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. Siiillaria. After Hirmer. 5. Catamites. 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 liv- ing 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 Magdefrau. 14. Cordaites. After Grand Eury. 15. Lebachia. A "transition conifer, " forerunner of pres- ent day conifers. After Magdefrau. 16. Pinus. Modern pine. After Magdefrau. 17. Acer. Common maple, an angiosperm whose leaves are also found among Tertiary fossils. After Magdefrau. 18. Rosa. The prairie rose, an angiosperm. 19'. Campsis. Trumpet vine, an angiosperm. Field Book PENNSYLVANIAN PLANT FOSSILS OF ILLINOIS Charles Collinson and Romayne Skartvedt LANTS THAT FLOURISHED 200 million years ago have made Illinois one of the best known fossil collecting sites in the world. The unusual abun- dance 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 through- out 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 condi- tions 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 genera- tions of plants lived and died, plant material fell into the swamp waters and, protected there from decay, accumu- lated. Frequently during the period, seas spread over the swampy lowlands, submerging the forests and covering [7] Reconstruction of Pennsylvanian Coal-forming Swamp 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 dur- ing 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. 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 num- bers. 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 sur- faces) are fossilization phenomena in which the actual plant, embedded in the surrounding background rock, was dissolved, leaving a hollow space (mold) that subse- quently filled with other material. A cast was thus formed that preserved the plant's external features. Most petrifactions are fossils in which silica, car- bonate, or other material permeated or replaced the inter- nal 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. PENNSYLVANIAN FLORA The far-reaching Pennsylvanian swamplands had a- bundant species of trees and other plants that long since have become extinct. Today's common deciduous trees were not present; flowering plants had not yet evolved. Instead, the tangled forests were dom- inated by giant ancestors of presently existing club-mosses, horsetails, ferns, conifers, and cycads. The undergrowth also was well developed, consisting mainly of ferns, fernlike plants, Sphenophyllum , and small club- mosses. The plant fossils give no indication of sea- sonal variations. The forests, evidently always green, grew rap- idly and abundantly, with foliage of unprecedented size and luxu- riance. Land animals were just beginning to develop and includ- ed sluggish, salamander-like am- phibians, large primitive insects, and a few small reptiles. The in- sects flourished as never before or since in the damp forests and Teneopteron attained remarkable size. Insects Aphthorob latt ina more than four inches long were common and some are known to have been more than a foot long with a wing- spread proportionately broad. Ancestors of the modern spiders, scorpions, centipedes (one fossil found in Illi- nois was twelve inches long), cockroaches, and dragon- flies are represented by several hundred species. The fossilized plants of Pennsylvanian time belonged to only a few main categories: scale and seal trees, an- cient scouring rushes (horsetails), herbaceous Spheno- phyllum , ferns, seed ferns, and cordaitean trees. SCALE AND SEAL TREES (Plate 1) Scale and seal trees were abundant during the Pennsylvanian Period and were important contributors to coal beds. Although dis- tantly related to the diminu- tive club-mosses and ground pines of the present, the trees grew on straight, slen- der trunks to heights of more than a hundred feet. Scale trees were so called because their numer- ous, closely set, spirally arranged leaves left scarred "cushions" on the branches and trunk, making them ap- pear scaly. Seal trees de- rived their name from the signetlike appearance of their leaf cushions. The two best known types belong to the genera Lepidodendron (scale tree) and Siii I laria(seal tree), and fossils of both are common in Illinois. Reconstruction of Lepidodendron (after Hirmer) 10 Lepidodendron had long, slender, somewhat tapering trunks. Some of the trees reached heights of more than 100 feet and measured more than two feet in basal diam- eter. The trunk ended in a spreading crown formed by re- peated dichotomous branching. The leaves were awl- shaped or linear, ranging from one to 30 inches long. The leaf cushions of Lepidodendron are diamond- shaped, longer than broad, and arranged in spiral rows around the trunk and branches. A different name, Lepi- dophyllum , is used for fossils of the long, bladelike leaf when it is found de- tached. Spores were borne in long cylindrical cones at the tips of the branches. Those cones referred, orassigned, to the genus Lepidostrobus bore both small spores (mi- crospores) and large spores (megaspores) in the same cones. Those in which only a large single spore, a somewhat seedlike struc- ture, was developed in a spore sac (sporangium) are referred to the genus Lepi- docarpon . The rather commonly found genus Stigmaria com- prises so-called "append- ages"which, although stem- like in structure, apparent- ly served as roots for the scale and seal trees. These appendages are identified by irregular spirals of circular scars (pits) that mark the attachment points of former rootlets. Sigillaria, although less common than Lepidodendron, was widely distributed during the Pennsylvanian Period. **fe~ Reconstruction of Stitllarla (after Hirmer) 11 It differed in growth habit from Lepidodendron in that it generally had fewer branches and not uncommonly was unbranched. Some species also possessed a thicker trunk, with hexagonal to elongate leaf cushions separated by vertical ribs. The trunk was crowned, in the manner of the modern palm tree, by a cluster of large, grasslike leaves. The detached leaves of Sigil- laria, extremely difficult to distin- guish from Lepidophyllum (leaves of Lepidodendron) , are referred to the genus Sigillariophyllumif pre- served as compressions and to Sigillariopslsif preserved as petri- factions. Unbranched Sigillaria trunks have been found that are more than 100 feet long and six feet in diameter near the base, but the average height probably was closer to 50 feet. Not all Pennsylvanian trees were large, however. Small forms are known, including the important undergrowth genera Lycopodites and Selaginellites. In woody types the trunk consisted of an inner region of conducting and supporting tis- sues, surrounding concentric corti- cal layers, and an outer layer of corklike bark. Although the fossil impressions of the various bark layers have been given separate generic names, these are not commonly used. Reconstruction of Calamites (After Hirmer) SCOURING RUSHES (Plate 2) Although related to the small, inconspicuous horse- tails of today, the ancient scouring rushes of the Penn- 12 sylvanian Period grew to the size of trees and were among the most widely distributed plant groups. Some of these plants attained heights of 40 feet or more, but the average was closer to 20 feet. The trunks were jointed and bore a whorl of branches at the joints (nodes). Their small leaves also grew in whorls at nodes along the smaller branches. Internodal regions were ribbed in the same manner as present day horsetails . Fossils of the trunks are assigned to the genus Catamites and quite commonly are preserved in sandstone and shale. The leaf whorls are placed in the genus Annular ia . One form commonly found in Illinois has long, pointed, needlelike leaves and is given the name Asterophyllites. Calamostachys , shown on plate 5, is one of the most common calamite cones. SPHENOPHYLLUM (Plate 2) The name Sphenophyllum refers to both stems and leaves of this extinct genus, which was related to the scouring rushes - note its resemblance to Annularia. A small herbaceous plant, Sphenophyllum formed much of the swampy undergrowth of the Pennsylvanian Period and is abundant among Illinois fossils. It had a slender, ribbed stem bearing whorls of delicate, wedge- shaped leaves, generally less than three-fourths of an inch long, attached around the stem in multiples of three. The cones of this group also are slender, delicate structures, bearing a number of sporangia, and are cor- rectly called Bowmanites , although they also have been called Sphenophyllostachys . These fossil cones fre- quently are found in Illinois. Sphenophyllum first appeared during the Devonian Period, some 300 million years ago, but did not become abundant until Pennsylvanian time. The genus continued through the Permian but died out in Triassic time. 13 Portion of fern frond showing sori on lower side of leaflets FERNS (Plates 1 and 3) True ferns, like those living in to- day's woodlands, were common in the Pennsylvanian forests. Some species attained heights of 30 to 40 feet. Their fronds (compound leaves divided into segments or leaflets) commonly were five to six feet long. True ferns do not produce cones or seeds, but spores, which develop in cases called sporangia . The sporangia are attached in clusters (sori) to the lower side or margins of the leaves. In modern ferns the sporangia may al- so occur on fertile spikes. The shape and position of the sori are used to iden- tify modern ferns, but because leaves that bear sori ("fertile" leaves) are rare among fossil specimens, the number, shape, and attach- ment of the leaflets and the pattern of the veins are more commonly used for identifi- cation. Because fossils of complete fern plants have not yet been found, separate names have been adopted for detached leaves, stems, and other parts. For example, the fossil stems of some Pennsylvanian ferns found in Illinois have been referred to two genera, MeQaphyton , whose leaf attachment scars are arranged in two vertical rows, one on either side of the stem, and Caulopteris, 14 Reconstruction of Meiaphyton (after Hirmer) Pecopteris Asterotheca Venation of seed fern leaflets Ptychocarpus whose leaf scars are arranged in a steep spiral that be- comes progressively flatter upward until near the top they appear to be whorled. When the stem is a petrifaction, with internal structures preserved, it is called Psaronius . The fronds are referred to a number of genera, but those most commonly found in Illinois are Pecopteris, Astero- theca, and Ptychocarpus. 1 '-% SEED FERNS (Plate 4) Seed ferns resem- bled true ferns ingen- I eral,but they produced seeds, borne on mod- ified leaves. Where spore sacs and seeds are absent, the leaves of seed ferns are dif- ficult to distinguish from those of spore ferns, although indi- vidual seed fern leaf- lets, called pinnae, are somewhat larger. Seed ferns includ- ed vinelike plants in the undergrowth and trees such as Medul- losa . Some tree gen- era were very tall, Medul losa Reconstruction and original drawing by Wilson N. Stewart 15 Alethopteris Odontopteris Mariopteris Neuropteris Llnopteris Venation of seed fern leaflets with trunks more than two feet in diameter. Unlike the true ferns, still living today, seed ferns declined stead- ily after the close of the Pennsylvanian Period and final- ly became extinct during Jurassic time. During Pennsyl- vanian time, however, they were much more numerous and varied than true ferns. Most of the common seed ferns found as fossils in Illinois can be referred to the following leaf genera: Alethopteris, Neuropteris, Odontopteris, Linopteris, Mariopteris (which may be a true fern), Cjjclopteris, and Spiropter is. Cyclop- j^M teris includes circular leaves ^^| that occurred at the base of leaves referable to Neurop- teris. Spiropteris includes "^p|(§p young leaves that had not "^^^m yet uncoiled and may belong ^^ to either true ferns or seed ferns. CORDAITES (Plates 1 and 2) Cordaitean trees, fore- runners of modern conifers such as pine and spruce, were important during the , ;"-i-8S^i$5! ^-'vV-.'*..- "'■■&*, *sm 16 Reconstruction of Cordaites (after Hirmer) Pennsylvanian Period forthey were distributed throughout the world. These trees, among the tallest plants of the time, sometimes grew more than 100 feet high. The cordaitean trunk was unbranched for three-fourths of the height of the tree and was topped by dense branches bearing large, simple, straplike leaves spirally arranged. The leaves had closely set parallel veins and measured from half an inch to three feet or more long. Internally, the structure of the trunks was similar to that of modern pine trunks. Casts of the pith are referred to the genus Art isia. The seeds were borne in clusters on branches in leaf axils. The Cordaites were major contributors to some coal beds. FRUITING BODIES (Plate 5) Fossils representing many kinds of plant reproduc- tive structures are found in Pennsylvanian rocks, but un- fortunately most of them are not attached to any identi- fiable part of the parent plant and they cannot be assigned definitely to a particular plant. Such fossils are referred to genera and species solely on the basis of their own characteristics, although, as in other fossil classifica- tions, such "form genera" are presumed to be parts of, or related to, the plants with which they are found in habitual association. A few such fossils, fairly common in Illinois, are illustrated on plate 5 to show their general shape and size. When attached to an identifiable leaf or leaflet, the seed is referred to as the seed of that leaf genus. For example, Holcospermum , a radially symmetrical seed with ribs and grooves, Codonotheca , a stalked, spore-bearing, lobed "cup, " and Neuropterocarpus , a flask-shaped seed with longitudinal ribs and grooves, all have been associated with Neuropteris, a leaf genus. 17 W • 0. en (0 Q) ■■ ■ l-l <-! -.