T-lGIsi no- n ecp.Q ILl,'r4UI& n: FOSSILS OF ILLINOIS CARLTON GONDII ILLINOIS STATE MUSEUM STORY OF ILLINOIS NO 1 1 STORY OF ILLINOIS SERIES No. L Story of Illinois: Indiaii and Pioneer, by V. S. Eifert. No. 2. Mammals of Illinois Today and Yesterday, by V. S. Eifert. No. 3. Exploring for Mushrooms, by V. S. Eifert. No. 4. Flowers that Bloom in the Spring, by V. S. Eifert. No. 5. Invitation to Birds, by V. S. Eifert. No. 6. Man's Venture in Culture, by Thorne Deuel. No. 7. The Past Speaks to You, by Ann Livesay. No. 8. Common Insects of Illinois, by A. Gilbert Wright. No. 9. Ancient Ways of Life, by Thorne Deuel (in preparation) No. 10. Amphibians of Illinois, by Paul W. Parmalee No. IL The Fossils of Illinois, by Carlton Condit Cost: 25c each; 20c each in lots of 25 or more Address all enquiries to the Museum Director, Illinois State Musuem, Springfield, Illinois STATE OF ILLINOIS William (L Stratton, (Governor DEPT. OF REGISTRATION & EDUCATION - ILLINOIS STATE MUSEUM Vera M. Binks, Director Thorne Deuel, Museum Director STORY OF ILLINOIS SERIES, No. 11 THE FOSSILS OF ILLINOIS A brief guide to the more common fossils in the rocks of Illinois by CARLTON CONDIT Springfifxd, Illinois 1957 Printed by authority of the State of Illinois) BOARD OF ILLINOIS STATE MUSEUM ADVISORS M. M. Leighton, Ph. D., Chairman State Geological Survey, Urbana Everett P. Coleman, INI. D. Coleman Clinic Canton N. W. McGee, Ph. D. North Central College Naperville Percival Robertson, Ph. The Principia College Elsah Sol Tax, Ph. D. L^niversity of Chicago Chicago D. ACKNOWLEDGMENTS The author wishes to express his gratitude to the Ilhnois State Geological Survey for material and information and to the Technology Press, Massachusetts Institute of Technology, and John Wiley and Sons, joint publishers of "Index Fossils of North America" by II. W. Shimer and R. R. Shrock, which was the source of many of the illustrations used herein. Thanks are due also the Geological Society of America and the University of Kansas Press for permission to adapt some illustrations appearing in "Treatise on Invertebrate Paleontology", R. C. Moore, Editor. FOR FURTHER INFORMATION CoLLiNSON, C. W. : Guide for Beginning Fossil Hunters. Educational Series 4, Illinois State Geological Survey, Urbana. Excellent gen- eral introduction to the subject. Well illustrated. GoLDRiNG, W.: Handbook of Paleontology, Part 1 — The Fossils. Handbook 9, Second edition, 1950, New York State Museum, Albany. Non-technical, for beginners, with special emphasis on New York fossils. Janssen, R. E.: Leaves and Stems from Fossil Forests. Popular Science Series, Vol. 1, second edition, 1957, Illinois State Museum, Springfield. Good illustrations and descriptions of fossil plant types found in Pennsylvanian Rocks of Illinois. La Rocque, a. and Marple, M. F.: Ohio Fossils. Bull. 54, 1955, Ohio Geological Survey, Columbus. Well written, well illustrated. Many Ohio fossils are found also in Illinois. Moore, R. C., Editor: Treatise on Invertebrate Paleontology. Geo- logical Society of America and University of Kansas Press, Law- rence. A multi-volume work of many experts, now (1957) in the process of being published. This is the definitive work, especially written for professionals. Amateurs can also get much of value from it. Shimer, H. W. and Shrock, R. R.: Index Fossils of North America. John Wiley and Sons, New York. Profusely illustrated, clearly written. Excellent for the serious amateur. Shrock, R. R. and Twenhofel, W. H.: Principles of Invertebrate Paleontology. McGraw Hill, New York, 1953. A technical, com- plete study of the subject for students and professionals. Unklesbay, a. G. : Common Fossils of Missouri, Bulletin, Handbook No. 4, 1955, University of Missouri, Columbia. Well illustrated, well written for the amateur. Emphasis on Missouri fossils, but much applies to Illinois as well. WHAT ARE FOSSILS? \'crv frequently a person wandering around a (juarry. or alonj^ a };ainst damafi;e or has for{>;otten extictly where he collected it and otluM- circumstanc(>s of the e\'(Mit. If specimens are ade(iuately cared for, cknuunl, and stored, and if careful notes are kept, the collector's pleasure in his specimens is much increased. For collecting in hard rock a geologist's hammer, with either a pick or chisel head is very useful. Some people prefer a brick-layer's hammer. ]\Iany people find that a cold chisel, or several of assorted sizes, are useful for removing individual specimens. These, however, get quite heavy before the end of the day. For soft material such as clay or soft shale beds, a surplus army sho\'el-hoe combination is light, strong, and useful. A notebook and a sharp pencil (with a means of sharpening it) are indispensable, as is a carrying sack or container of some kind. Old newspapers make ideal wrapping material, together with some softer paper for particularly delicate fossils. Try always to have specimens well protected against knocks and scratches and enough paper around them to give a certain amount of cushioning. To keep the notes in order, a number may be marked on the back side of the specimen or on a scrap of paper wrappc^d with the specimen and the notes then entered after a corresponding luuiiber in the notebook. The notes should contain exact locality infoi'mation (so that someone else could find the locality .just from tlie notes), the date, collector's name, rock strata name, and any other appropriate information. As soon after returning as possible, the specimens should be unwrapped and set out in an orderly way for examination and cleaning. Ordinary water with perhaps a small brush like a stifl" toothbrush will clean out mud, clay and most shale particles. Careful application of muriatic acid or even vinegar will help to remove limestone. Care must be exercised here, however, as the acid may also eat away the fossil. Oxalic acid sometimes helps to remove stains or certain kinds of cementing materials. In many cases, nothing but the slow chijjping away of the surrounding material with small chisels and needles will i'i>veal the fossil; this is a work of patience and skill. Once cleaned and accompanied by an adell. The folding varies from a few .sharp bends in the early types to extremely complex patterns in the later types. This characteristic makes the ammonoids extremely important. Individual species can be recognized from an incomplete specimen, and studies of the progressive changes in the pattern of folding through time has taught us a great deal about evolution. 15 Phylum Arthropoda (ar-thr6p-6-da, jointed-foot) The arthropods are characterized in general by a segmented body covered with a hard shell made of chitin, a substance similar to finger- nail, jointed between all or some of the segments, and possessing jointed chitin-covered legs. Living arthropods such as insects and spiders are very complex in internal as well as external structure and are regarded by some as the most highly evolved of all animals. They certainly are more highly evolved than all groups except the vertebrates. This phylum is the largest of all, in terms of numbers of species, and in terms of number of individuals is rivaled only by the protozoa. A great many common and little known animals are included in the phylum. Examples of common ones are insects, spiders, crayfish, crabs, and barnacles. In the fossil record it is also abundantly repre- sented in Illinois rocks. Three classes are important in the fossil record. Class Crustacea (krus-ta-she-a, crusted) This class includes a large number of living and fossil animals of which only three groups are abundant enough in Illinois rocks to merit discussion here. These three groups are ranked as subclasses, that is, divisions smaller than classes but larger than orders. Bumastus Beconstruction of trilobite (after Chicago Natural History Museum) Subclass Trilobita (tri-l6-bi-ta, three-lobed) The trilobites are wholly extinct; our knowledge of them is chiefly about their hard parts, augmented by a little gained from unusually well preserved specimens showing some de- tails of the soft anatomy. The hard parts consist of the outer 16 shell or case, made of chit in with .sonic lime added, which covered the back of the animal but apparently not the under- side. The shell is divided into three more or less distinct parts or lobes both lengthwise and crosswise. Lengthwise, the divisions are the head, the segmented thorax, and the tail, in which the segments are more or less obscure. Cross- wise, the lobes consist of the central axial lobe, usually rather rounded and high, flanked by two pleural lobes which are rather flat. Since the hard case co\(»red only the back of the animal, many trilobites developed the habit of coiling up, perhaps when disturbed, much as a sow bug does today. In this way the soft underparts would be given better protection. How^ever, this often did not save the animal's life because w^e find a lot of fossils coiled up in a futile attempt to avoid death. So far as we know, all trilobites were marine animals. Subclass Malacostraca (mal-a-k6s-tra-ka, soft shell) This group includes the living crabs, lobsters, crayfish, shrimps, and similar forms, living in both marine and fresh waters. They are of great importance toda}^ both in the ecology of the sea and as a source of food for man. Their fossil record is somewhat scanty, but enough of them are found so that the collector should always have the group in mind. Most of the fossils are sufficiently like living forms to be readily recognized as members of the subclass. Subclass Ostracoda (os-tra-ko-da, shelled) Most ostracodes are so small that they can be seen with the unaided eye only as specks of white or brown on rock surfaces. With the aid of even a low power glass, however, their details are brought out. They are most likely to be found in shales of either marine or fresh water origin. Ostracodes bear little superficial resemblance to other crustaceans. The outer covering (and the only part found fossil) consists of two oval or nearly o\al .shells similar to a very tiny clam. Their small size and various siu'face markings show them to be ostracodes. In spite of this chun-like appear- ance, the internal structure of li\'ing forms clearly demon- strates their relationships to the Crustacea. If, like the grap- tolites, they were all extinct, we would no doubt find it very puzzling to classify them correctly, and there would be several different opinions as to their proper place in the animal king- dom. Class Insecta (in-sek-tii, cut into) The in.sects, in terms of the number of different kinds, con- stitute the largest single cla.ss of animals. They have IxM-ome adapted to almost every type of habitat from the hottest tropics to the polar regions. Among them they po.s.sess a bewildering 17 variety of structures, but they all have certain basic characters in common which mark them off from all other animals. They have a body composed of a distinct head, middle section or thorax, and abdomen. They are six legged, with the legs borne on the segments of the thorax. Most forms have one or two pairs of wings also borne on the thorax. They are all air breathers during the adult stage. Fossil insects are not uncommon in certain rocks in Illinois and are readily recognized by some of the characters listed above. It is interesting to note that the fossil insects found in Illinois all belong to what are regarded as the primitive, less highly evolved orders. Class Arachnoidea (a-rak-noi-de-a, spider-like) This class has the head and thorax fused together, with eight walking legs on the thorax portion, two pairs of appendages around the mouth for eating and sensory use. There are no wings; poison claws or glands are present in some members. Both aquatic and land-dwelling types are included. This class has a very long history, extending from the Cambrian down to the present. It is represented today by spiders, ticks, scorpions, and in the sea by the horseshoe crab. Among the fossils that may be found in Illinois rocks are the eurypterids (u-rip-ter-ids) , marine animals superficially resembling scorpions but actually more closely related to the horseshoe crab. These animals had a ''head"; an elongated, rounded body con- sisting of many segments; and a long, jointed tail. Eight legs and some other appendages were attached to the "head." Often one pair of legs was greatly enlarged to paddle or flipper-like organs. A few examples of ancient horseshoe crabs have been found in nodules from beds associated with the Pennsylvanian coal de- posits. Several other types of arachnoids have also been found in these beds although they are not abundant. Phylum Chordata (kor-da-ta, cord) This phylum is sometimes called the Vertebrata because most of its members possess a backbone made up of a string of bones called vertebrae. A large number of different kinds of animals belong to the phylum, including man. Fossils of chordates usually are of three types: fish scales, teeth, and bones. In Illinois rocks most chordate fossils are of fish, either scales or teeth. The scales appear as rounded or oval thick shiny plates, usually dark in color, and having delicate ridges or fine lines on the surface. Fish teeth are of many shapes, but all show a hard shiny surface of enamel and another rough fibrous portion where the tooth was attached to the jaw. Bones of vertebrates are usually found in the glacial deposits that lie near the surface. It is rare for the whole skeleton to be found, but frequently enough parts of the animal can be recovered so that the animal can be identified. A large number of fossil elephants and other 18 animals have hccii louiul in the j^lacial deposits of Illinois. The Museum has one request to make of fossil hunters. Fossil hones are often very fragile and have to be collected with extreme care and with special equipment if thej'^ are to be preserved. If you find what appears to be a considerable portion of a skeleton, please do not attempt to dig it (Hit, but leave it there until you have notified the Museum. We will send someone ecjuipped to collect it in a way that will j)rescrve it for scientific study and display. FOSSIL PLANTS The record of fossil plants in Illinois is not very extensive except in beds of Peimsylvanian age and scattered fossils in Pleistocene glacial deposits. We will therefore not give a complete classification of plants but mention only those groups likely to be encountered by fossil hunters in the state. Di\'isiou Sphenopsida (sfe-n6p-sl-da, ivedge-like) The genus Equiseium is the only living representative of this group. Native species, commonly called horsetails or scouring rushes, can be seen growing in moist sunny places. They are small plants but illustrate the essential characters of the group. Many fossil members reached the size of large trees. The stems are hollow, ribbed or grooved vertically, jointed at intervals, and bearing a ring of small leaves or branches at the joints. The spore-bearing bodies, borne at the end of some stalks, are cone- shaped with the scales enlarged at the end into six-sided shields that protect the spore sacs behind them. Fossil sphenopsida show most of these structures. We find casts or impressions of the stems with lengthwise grooves and ridges, and occasional joints. Some- times the joints show a ring of pits that mark leaf or branch scars. Leaves are found as prints of rosettes of wedge-shaped or oval leaves, often strung along a thin stem. Spore cones are usually rather poorly preserved, but sometimes the central axis and the closely spaced scales can be recognized. Division Lycopsida (ll-k6p-si-da, lycopod-Uke) This group also once included large trees but is now represented by small, insignificant plants. "Ground pine", or club mosses, are minute plants found in moist shady environments and are likely to be missed by casual ol)servers. In the past, however, particu- larly in the Pennsylvanian period, they were some of the largest trees in the forests. Impression of the stems, or casts of them and the roots, are the most common fossils. Occasionally, leaves or spore-bearing bodies are found. Leaves are small scale-like or larger strap-like impressions; spore-l)earing bodies are small cones of overlapping scales. The two common fossils are Lepidodetulron and Sigillaria, and the roots go by the name of Stigmaria. 19 Division Pteropsida (te-rop-si-da, feather-like) This division is so named because most members of it have broad, expanded leaves. It includes all of the higher plants now living as well as some groups that are wholly extinct. Three groups are likely to be found in Illinois: Ferns — ferns are plants that reproduce by means of spores, tiny dust-like bodies contained in sacks on the undersides of the leaves. Occasional fern leaves are found which can be recognized by presence of these spore sacks. Seed ferns — these are wholly extinct plants which bore fern-like leaves but reproduced by means of seeds. Both parts of the plant are common in rocks of the coal age. It is difficult to tell whether a given leaf is a fern or a seed fern, unless you happen to find the leaf and seed attached to each other or unless you know which leaves are seed fern leaves. In general, in Pennsylvanian rocks, the chances are that the leaf is a seed fern since they were far more abundant and much larger trees than the true ferns. Flowering plants — in the glacial drift and related deposits that lie at the surface of much of Illinois logs, peat, seeds, leaf prints (sometimes) and other plant debris is encountered. Much of this material is too poorly preserved to be identified, but sometimes well preserved specimens are found. If so, they will closely resemble living plants and may be identified by referring to botany books. 20 TUK FOSSILS OF ILLINOIS < 'ambrian Fossils The C'anil)riaii period was the first to contain abundant Hie that left remains as fossils. It is unfortunate that ('ainl)rian rocks are of such limited exposure in Illinois because these earliest fossils are of great interest, both from the standpoint of their origin and in their position of being ancestral to all succeeding forms. To consider the first point: While it is true that few fossils are found in rocks earlier than the Cambrian, it can scarcely be true that animals and plants did not exist prior to that time. The great diversity of forms known from Cambrian time, although not in Illinois rocks, and their immense complexity of structure, wlien compared to single- celled forms, clearly shows that as much evolution took place prior to the Cambrian as has occurred since that time. Presumably, then, ecjual lengths of time are involved. It is much more probable that plants and animals did not leave much of a record before the Cambrian because they were not equipped with hard parts. A hard shell or bony skeleton or woody tissue is almost a necessity if a fossil is to be preserved; an organism lacking such a structure is likely to be eaten or to decay before its body can be buried in sediment. We note that many of the earliest Cambrian fossils have small and imperfectly developed shells, indicating that at that time they were just l)eginning to develop such structures. As to the second point, we observe that almost all of the major groups of animals and plants are represented in Cambrian rocks, either at the beginning or before the end of the period. The others, not known from Cambrian rocks, appear shortly after and in such highly developed form that they too probably lived in the Cambrian but escaped preservation. All of the animals and plants of the Cambrian that we know are marine forms. The two most abundant groups of animals in the Cambrian are the trilobites and the brachiopods. Common Cambrian types of these animals are represented on page 28. The brachiopods are enclosed in two shells that are hinged together on one side. When the animal is alive, these shells are opened slightly permitting sea water to enter and carry oxygen and small particles of food to it. When the animal dies the shells, sometimes together but often separated, become buried in mud or sand on the sea bottom and thus enter the fossil record. The earliest brachiopods had small shells with simple circular or oval outlines and little ornamentation or sculpturing on the outer surfaces. Shortly after the beginning of the Caml)rian, we find shells much larger and with various types of ridges and grooves and inter- locking margins. All these characteristics made the shell stronger and were difficult to open by the brachiopods' enemies. Expansion was also rapid among the trilobites. These ancient (and distant) relatives of living inse(;ts first apptvucd in the earliest Cambrian as small, simple fcjrms with few body segments and little ornamentation or sculpturing. Soon, however, they developed into a wide variety of forms with many types of ornamentation such as 21 spines, knobs, and ridges. Trilobites expanded in numbers and kinds enormously during the Cambrian so that some upper Cambrian fossil- bearing beds contain more trilobites than all other fossils together. Another group of fossils found in Cambrian rocks are the cystoids. Upon death, the plates of the cystoids usually became separated, and it is rare to find a complete specimen. However, literally thousands of plates of the body or stem are present in some sedimentary rocks, usually limestones. Cystoids are wholly extinct, so we know prac- ically nothing of the details of their internal organs. Ordovician Fossils The Ordovician period was one of the great periods for the ex- pansion and spread of animals, and it is one of the richest in fossils. There are several reasons for this. It was a long period, and broad shallow seas were widely extended across what is now the continental land. The climate was mild and even. The descendants of Cambrian animals flourished in these favorable conditions, multiplied enormously, and evolved into hundreds of different types. At this time all of the major living phyla are represented by fossils, even the last to rise, the Chordata. The trilobites reached their greatest abundance at this time, and although they continued to inhabit the seas of the earth, they steadily declined until their ultimate extinction. As a result of rapid evolution, they developed into many different types, often very different from the Cambrian types. Many of them developed complex spines, or intricate sculpturing, or greatly enlarged eyes. Many of them were able to coil up so that the unarmored lower side was protected. They evidently lived in a wide variety of habitats — some swimming in the open water, some crawling along the bottom, some perhaps burrowing in the soft mud of the sea floor. At this time the trilobites reached their greatest size, the largest one ever found attaining a length of 27 inches. Graptolites, those mysterious fossils which no one is sure exactly what they represent, are found in Ordovician rocks. They appear as thin black lines on bedding planes of shales and limestones, very often with sawtooth edges. Some are single, some are branched, and rarely they are coiled. In spite of the cjuestion of their true identity, they are very interesting and useful fossils. They were apparently very widespread, with identical forms being found in Australia, England, and the United States, for instance. Also they evolved rapidly, so that in beds or layers only a few feet apart vertically they are greatly differ- ent. Thus by using graptolites it is possible to very accurately deter- mine the relative ages of rock layers in Avidely separated areas. Corals and crinoids were both present in Ordovician times, but apparently not very abundant, for their fossils are few. They were destined to expand and flourish a little later in the history of the earth. Bryozoans also are found in rocks of this period and are extremely important to the professional geologists. To study them, however, requires rock grinding equipment and powerful microscopes; so the average amateur can do little with them. When one considers the extremely favorable conditions for ex- pansion and development of life brought by the Ordovician, one is led 22 to wonder what mif^lit iiuvo happL'iied if enviroiimentiil factors had been less favorable. From the relatively scanty fauna of the lower Cambrian, the upper Cambrian and Ordovician offered opportunity for rapiil and witlespread expansion, both in kinds and in individual members. This ^nvv a sound foundation for later evolution, leading to the development of liviiifj; animals and plants. Perhai)s, if tough conditions had existed, the animals of the time would ha\'e been barely able to maintain themselves, and subsequent evolution might ha\e l)een delayed millions of years. It is possible, indeed, that you would not now be reading this speculation if the Ordovician period had Ix-cn one of restricted seaways and harsh climates. Silurian Fossils Generally for North America, the Silurian offered far less pleasant conditions for the animals of the time than did the Ordovician. Seas were narrower, climates more severe, and in some places great inland seas became so heavily charged with salt that thick beds of rock salt now lie buried where once these saline seas existed. In the Illinois area, however, conditions were not quite so extreme. The Illinois Silurian rocks are largely limestone and dolomite and are often rich in fossils. For the first time, corals became very abundant and grew in great masses forming large reefs similar to those now growing in warm eciua- torial seas. Several of these reefs have been exposed in quarry opera- tions where one can see the irregular mass of the reef itself rising through the more evenly bedded surroimding materials. Such places have rich fossil of corals, bryozoans, brachiopods, and crinoids. The environmental conditions along these reefs were very different from those in the areas between the reefs. As they do today, the reefs extended up from the sea bottom, perhaps even rising abo\-e the surface of the ancient seas. As a consequence, wave action was intense. As we look at these reefs we can see some of the effects of the poiuuling surf: blocks broken off, coral heads lying upside down, and sloping beds of limy and shelly fragments, all indicating the action of waves. Between the reefs on the smooth quiet bottom of the sea, little of this effect can be noted. The water was usually calm there, and deposition of lime and mud proceeded slowly and regularly. As a result of the.se environmental differences, the animals that occupied the reef areas were different from tho.se in the (juiet inter- reef areas, and the careful collector can readily see these differences in the fossils he finds. Crinoids and their relatives, the cystoids, were likewise very abun- dant. Some rocks of Silurian age consist of more than half of crinoid fragments — cup plates and stem segments. Often complete cups can be found, especially of the smaller forms. Brachiopods continue their advance and reach large size and considerable complexity of shell structure. Another aspect of evolution is seen in the absence of several groups that were found in the Cambrian and Ortlovician rocks. This is the method of evolution: development of new forms and extinction of old forms so that the population takes on an entirely different aspect. Why some forms die out and irhi/ new forms develop are otlier (juestions 23 which cannot as yet be completely answered. It may be said, however, that the Cambrian and Ordovician forms that failed to last into the Silurian were largely those with small, simple shells with simple hinge- lines. Perhaps this type of shell afforded insufficient protection against the animals' natural enemies; we cannot say for sure. The trilobites had by now passed the peak of their evolution: only about half as many are known from Silurian rocks as from Ordo- vician rocks. Those that survived followed either of two general lines of evolution. Some remained conservative, closely resembling their Ordovician ancestors; others evolved rapidly into many weird shapes. Some of these developed numerous long spines while others lost most exterior markings to the extent even that their three-Iobed nature was obscure. Among the cephalopods, the nautiloids had by now reached the peak of their development and were fated to decline in the succeeding periods. Several peculiar types of nautiloids are found in Silurian rocks. Some are spirally coiled instead of the normal plane-coiling, and some have narrow, constricted openings which must have interfered with the animals' free movement. Some paleontologists regard these odd types as an indication that the group as a w^hole is close to decline and ex- tinction, and, indeed, such conditions seem to arise frequently in like instances. On the other hand, this theory cannot really be proved, although many examples supporting it are found in the fossil record. The other, and later, group of cephalopods, the ammonoids, appear in the late Silurian. The ammonoids have folded sutures or partitions, and in these rocks we find the first form with relatively simple folds but still more complex than the ancestral nautiloids. Devonian Fossils In other parts of the world great events took place at the end of the Silurian and brought with the Devonian important changes in environments. These scarcely affected the Illinois area, however, in which the relatively simple recurrence of marine advance and retreat continued. As in the Silurian, the Devonian seas deposited a series of limestone beds, each one scarcely to be distinguished from the ones above and below and all similar in appearance to the Silurian beds below\ Such is not the case, however, with the fossils of the Devonian. Due in part to normal progressive evolution and in part to the invasion of new forms from elsewhere, Devonian life forms are readily disting- uished from Silurian. Crinoids, corals and brachiopods continue to be abundant. Trilo- bites become fewer, as do the nautiloids, whereas the ammonoids become both more abundant and more complex in structure, particularly in the folds of the partitions. Fish were apparently very abundant in the Devonian. Some beds contain literally thousands of teeth and spines and scale plates of primitive fish. A curious and so far unexplainable feature about these fish remains is that they occur abundantly in a bed maybe a foot or so thick and then are almost completely absent in the beds above and below. Perhaps the fossil hunter can find some evidence that will suggest an explanation of this curious distribution. 24 Mississippian Fossils The early part of the Mississippian period saw the continuation of Devonian conditions in the Tlhnois area with the deposition of much hmestone in tlie clear seas. The latter part of the period witnessed a change in the sediments with the deposition of many beds of mud and sand, now having become shale and saiulstone. These bods reflect the elevation of land (probably to the east) causing the rivers there to flow faster, carrying sand and mud into the seas that covered the Illinois area. These changes in environment affected the life of the times, and we find that the fossils of the shales are greatly (lirf("rent from tiiose of the limestones. Corals, crinoids and brachiopods all show reduction in the Mi.ssis- sippian although they were still numerous enough to leave abundant fossils. The blastoids, which had been in existence since the Ordovician, expand rapidly in the Mississippian. Some beds contain literally millions of fossils of these extremely neat and dainty fossils. The trilobites are further reduced in this period with only a rela- tively small number of species still living. It is interesting to note that the highly ornamented forms that developed earlier are now extinct, and only the older, plainer, more conservative types have survived. This again is an example of something seen over and over again in the fossil record: the first forms of a group are simple, from which evolve more complex types, and with the approaching extinction of the group the complex ones disappear before the earlier, simple types. It strongly suggests that the newer, specialized types, though well fitted for a particular set of conditions, are less likely to survive changing conditions than the older, conservative, more generalized forms. Among the cephalopods, the nautiloids declined in al)undance and the ammonoids increased until the two groups are about e(}ual. As with other groups, the old conservative lines exist side by side with later more complex, ornamented tj'pes. Straight shelled forms still lived, some of which grew to great size: Some shells are eight inches in diameter and five feet long. Curved and coiled forms were more abundant showing all degrees of coiling from open loose coils to over- lapping coils. Pennsylvanian Fossils Profound changes occurred in Illinois in Pennsjdvanian time. This area, and much of that in adjacent states, was a sort of border-land between rising mountains to the east and a great inland sea to the west and southwest. For millions of years the whole region suffered alternate submergence under advancing seas and emergence, each of short duration and repeated over and over. This resulted in a distinctive character of Peniusylvanian sediments with thin beds of sandstones, shales, coals, and limestones lying one on top of the other in an often repeated se(iuence. Some beds, notably the limestones, are marine in origin and contain marine invertebrate fossils. Others, such as the shales and clays lying next to coal beds, are of land origin and contain fo.ssil plants and land animals. The coal beds themselves represent the accumulated plant material that formed 25 in great swamps bordering the inland seas when they were withdrawn westward. We therefore find in Pennsylvanian rocks two distinct groups of fossils: the marine forms similar to those of earlier periods; and a new group representing animals and plants that lived on land. Among the marine forms, our old friends are much in evidence. Brachiopods are common, corals abundant, crinoids widespread, but trilobites are rare. Nautiloids are few and ammonoids abundant; fish were widespread, as shown by the teeth, spines, and scales that are often found. The protozoa are represented by numerous tiny foraminifera called the fusilinids, each one about the shape and size of a grain of wheat. These fossils are all found in the limestones and shales that were deposited during the times of submergence. In the beds deposited on land, sometimes in the coal itself but more commonly in the clays and shales immediately above or below the coal, we find leaves, stems, and seeds of a wide variety of land plants together with less common fossils of insects, clams, snails, Crustacea, amphibians, reptiles, and fish. These fossils, for the first time in this area, give us an idea of the nature of the land population that existed contemporaneously with the better known marine forms. The commonest plants are the seed ferns, represented by imprints of leaflets or larger parts of fronds and occasionally by seeds, casts of stems, and other parts. Spore-bearing plants are also represented — by lycopods and horsetails. Occasionally true ferns are found although these are never as common as the seed ferns. It is these same plants that went to make up the coal, but there the destruction of the plant tissue has gone so far that few fossils can be recognized. Cretaceous and Tertiary Fossils After the deposition of the Pennsylvanian rocks, the next younger rocks are those deposited in the Cretaceous period approximately 150 million years later. What happened in this long interval in the Illinois area, we do not know. It may have been low lying land, receiving no sediments; or perhaps it was submerged, with subsequent uplift and erosion of the earlier deposited beds. In any case, conditions all over the world were greatly changed by the time the Cretaceous beds were deposited, and, naturally, the animals and plants of the world were also much different. In Illinois, the Cretaceous deposits are found only in the extreme southern part of the state, and even there they are thin and offer few good exposures. They represent near shore deposits of a sea that extended into Illinois from the south or southwest, and they contain a few marine organisms and occasional land fossils that were washed into the sea from the neighboring land areas. About all that will be found are some pelecypods similar to oysters and some marine snails. Perhaps a few leaf-prints from trees very much like living trees may be found. Tertiary beds are also exposed at the surface only at the southern end of the state where they lie on top of Cretaceous beds. Since both sets of beds dip to the south, the overlying beds are even farther south 26 than the older Cretaceous beds. The Tertiary beds are soft sands and clays, deposited aloii}? the shore of a shallow sea that extended up from the south. \'ery few fossils have l)een found in them. Some gravel beds, believed to be stream deposits, are also found. The.se might well contain bones of mammals, but such finds ha\'e not been recorded. Pie istoce n e Fosn lis Lying at the surface over most of Illinois (except at the soutiiern and northwestern parts) are the glacial deposits of Pleistocene age. This materitd is mostly soft and crumbly aiul is thought of as ordinary dirt. Occasionally in this material some types of fossils are found. Bones and teeth of mammals such as elephants, bison, beavers and others, all very similar to living forms, are sometimes found. The.se occur usually in gravel and sand beds made by streams from the ice front. Occasional beds of peat are found which contain recognizable fragments of plants, again indistinguishable from living plants, al- though many of them do not grow in Illinois. Here and there, in gravel l)eds or clay deposits logs and branches have been found. If the fo.ssil hunter will examine all new excavations, such as highway cuts, deep basements, and the like, when opportunity o.ffers, he may occasionally discover some Pleistocene fossils. 97 CAMBRIAN FOSSILS 1. Cryptozoon iVo natural size) 2. Crustacean Pseudognathus (6x). Upper figure is head; lower is tail. 3 & 4. Gastropod Palaeacmoea, top and side views. 5. Gastropod Proplina, side view. 6. Brachiopod Lingulella (7.x) 28 ORDOVICIAN FOSSILS 1 & 2. Brachiopod Platystrophia, top and end views (2x) 3. Cephalopod Michelinoceras 4 & 5. Brachiopod Hesperorlhis, top and side views 6. Brachiopod Resserella (2x) 7. Brachiopod Zygospira (2x) 29 ORBOVICIAN FOSSILS 2. Brachiopod Plaesiomys, side and top views 3. Brachiopod Rafinesquijia 4. Brachiopod Plectorthis 5. Pelecypod Saffordia 30 ^llir ORDOVICIAN FOSSILS 1. Gastropod Tmchonema 2 & 3. Brachiopod Nhyncholrema, side and bottom views (2xj 4 & 5. Brac'hiopod Ileberlella, top and side views 31 ORDOVICIAN FOSSILS 1. Coral Streptelasma 2 & 3. Gastropod Salpingostoma 4. Gastropod Horotoma 5 & 6. Gastropod Ecculiom-phalus 32 SILURIAN FOSSILS 1. Brachiopod Penlamerus 2. Trilobite Flexicalymene (2x), coiled 3. Crinoid Crotalocrinites (2x) 4. Trilobite Bumaslui, head only 33 SILURIAN FOSSILS L Colonial coral Favosites (Hx) 2. Colonial coral Halysites (Ix) 3. Colonial coral Syringopora (Ix) 4. Crinoid Eucalyptocrinites 5. Brachiopod Dalmanella (2x). interior of shell 34 SILURIAN FOSSILS 1 & 2. Brachiopod Petttamerus, H^x), top and bottom view of interior mold 3. Crinoid I'triechocrinusj incomplete calyx or cup 4. Brachiopod Atrypa, top view 5. Coral Halysites, the chain coral 6. Gastropod Pleurotomaria, internal mold (J^x) 3.") DEVONIAN FOSSILS 1. Trilobite Phacops (2x) 2 & 3. Brachiopod Airypa, side and top views 4 & 5. Brachiopod Pholidostrophia (2x) 36 DEVONIAN FOSSILS 1. Horn coral Amplexus 2. Brachiopod Lepdaena (2x) 3 & 4. Brachiopod Schucherlella (2x) 37 MISSISSIPPIAN FOSSILS 1 & 2. Colonial coral Lithostrotionella 3. Blastoid Pentremites 4. Brj'ozoan Archimedes 5 & 6. Brachiopod Terebratula 38 MISSISSIPPIAN FOSSILS 1. Brachiopod Productua 2. Bnicliiopod Spirifer (3^x) 3. Brachiopod Rhipidomella 4 & 5. Bracliiopod Cyrlina, top and side views 6. Cephalopod Muensteroceras 39 MISSISSIPPIAN AND PENNSYLVANIAN FOSSILS 1 & 2. Mississippian brachiopod Cyrtina (3x) 3 & 4. Pennsylvanian brachiopod Composiia, top and bottom view 5 & 6. Pennsylvanian brachiopod Mesolobus (2x) 40 /li-^-». -^^i.^"^ >^'-M i-s^K* ^ /••I . ■■•• .•■ ■.-;." •.■• K.V4K Si"" .' / -I*! Pj^ili^- PENNSYLVANIAN FOSSILS 1 & 2. Brachiopod Derhyia, top and bottom views 3 & 4. Brachiopod Marginifera, top and bottom views 5 & 6. Brachiopod Juresania, top and bottom views 41 PENNSYLVANIAN FOSSILS 1. Protozoa Fusulina, a mass of fossils in rock (Ix) 2 & 3. Protozoa Fusulina (5x) 4. Brachiopod Orbieuloidea (2x) 5. Clam Alloristnei 42 PLEISTOCENE •PL.IQCENE?_ EOCENE CRETACEOUS SILURIAN SERIES. GROUP OR FORMATION GLACIAL OHIFT UAFAYLTTt ORAveU WILCOX SANO MIDWAY SAND MCNAIRY SAND MCLEANSBORO GROUP CARBONOALE GROUP TRADCWATER GROUP CASEYVJLLE GROUP PRE-CAMBRIAN PRE-CAMBRIAN CHESTER SERIES MERAMEC GROUP OSAGE GROUP STE GENEVIEVE LIMESTONE ST LOUIS LIMESTONE SALEM LIMESTONE WARSAW SHALE KEOKUH. LIMESTONE BURLINGTON LIMESTONE FERN GLEN LIMESTONE KINDERMOOK GROUP GRAND TOWER LIMESTONE WAPSIPINICON LS. CEDAR VAlltY LS. CLEAR CREEK CHERT BACKBONE LIMESTONE GRASSY KNOB CHERT BAILEY LIMESTONE NIAGARAN DOLOMITE ALEXANDRIAN DOLOMITE MAQUOKETA SHALE GALENA CKIMMSWIC^) DOLOMITE PLATTIN CPLATTE VILLE) LIMESTONE Sr PETER SANDSTONE SHAKOPEE DOLOMITE NEW RICHMOND SANDSTONE ONEOTA DOLOMITE TREMPEALEAU DOLOMITE FWANCONI A DOLOMITE GALESVILLE SANDSTONE EAU CLAIRE SHALE MT SIMON SANDSTONE FOND DU LAC SANDSTONE CRYSTALLINE ROCKS "n-^ -x;'-^"r:Vc;K i i . r r I -; I Tun: ^^ /. /. /. /- /_/ / / Z GEXEHALIZED GEOLOGIC COLUMN OF ILLINOLS (Reprinted from Illinois Geological Survey, Bulletin 30, Bedrock Topography of Illinois by L. Horberg.j 43 N A A PLATE I SKETCH MAP Sliowin9 [he DisVn'buhon of BEDROCK STRATA In Illinois Explanation of the Map d] Tertiary ■ Devonian ^Cretaceous DSilurian ^Pennsylvanian ^Ordovician ^Mississippian SCombrian 44 UNIVERSITY OF ILLINOIS-URBANA 507IL61ST C006 STORY OF ILLINOIS SERIES. SPRINGFIELD 11 1957 3 0112 025310993 ILLINOIS £a/td o^Xlneo&t/ \