The man and his flint blade are dwarfed in comparison to the huge, hairy creature he and the hunting party have stalked and killed beside the lake. He carves into the massive leg, thick as a

Fossil Hunting in Ohio State Parks Identifying fossils takes careful observation and lots of imagination. In some fossils, the entire skeleton or outer shell of an animal is preserved, while others are part of an animal or merely an impression of an animal etched in stone. Two of Ohio's very best fossil hunting beds are found in Ohio State Parks. At Hueston Woods State Park in Preble and Butler counties and Caesar Creek State Park in Warren County, outcrops of the world-famous Cincinnati limestone teem with fossils of sea creatures that lived during the Ordovician period. Fossils you may find at Hueston Woods or Caesar Creek include: Brachiopods -- resemble clams, but their top and bottom shells are not identical; the top shell rises in the center, and the bottom shell is indented. The shells are wing-shaped, and have deep ridges. Mollusks are most often represented by two members; pelecypods -- are similar to modern clams with two identical shells. Their fossils may include an impression of both shells, just one shell, or just the nut-shaped interior of the clam; and gastropods -- look similar to modern snails. Cephalapods -- are most often shaped like long cylinders wrapped in coils. Some are curled in a spiral like their modern relative, the nautilus. Bryozoans -- were tiny individual animals that formed colonies often shaped like small twigs. Some bryozoan colonies are flat or fan-shaped with interesting textures. Cnidarians -- are best represented in Ordovician limestone by the horn corals. These ancient corals lived alone, rather than in colonies like modern corals, and are shaped like a bull's horn. Arthropods -- are best known in the fossil record through the trilobites. They ranged in length from a little over one inch to nearly one foot. Their oval bodies featured large bulging eyes and deep horizontal ridges along their backs divided length-wise by two deep grooves. Some trilobites are found rolled up, with their tails tucked close to their heads. Echinoderms -- are most often found as a body part of a crinoid, or sea lily. The crinoid stem resembles a stack of disks forming a column. A five-pointed star shape may be visible at the end of the column, in cross-section. Fossil collecting is permitted for non-commercial purposes in designated areas at Hueston Woods and Caesar Creek state parks.

tree trunk, to claim the precious meat that will feed his gnawing hunger.

In 1983, ten thousand years after the hunting party butchered the unfortunate mastodon, its nearly complete skeleton was found in a bog in Licking County, near Newark. The mastodon and its close relative, the wooly mammoth, were plant-eating, fur-covered giants with huge tusks, similar in size and shape to modern elephants. The mastodons and mammoths lived alongside other super-sized mammals, including ferocious sabertooth tigers, menacing dire wolves, giant beavers as big as bears and ground sloths the size of oxen. They were well-suited for life in Ohio during the Pleistocene Epoch of earth's history, 1.6 million to 10,000 years ago. During that time frame, also known as the Ice Age, slow-moving sheets of mile-thick ice called glaciers crept south into Ohio and neighboring states from the tops of mountains in Canada. The glaciers gradually advanced and retreated four times across the northern and western two-thirds of Ohio, flattening hills, leaving behind piles of rubble and carving chilly lakes. Only the southeastern third of the state remained untouched by the crushing force of the ice.

All of these magnificent mammals are extinct now. We know they existed because parts of their bodies have been preserved after death as fossils. In some cases, like the Licking County mastodon, the animal's body fell or was pushed into a lake and sank to the bottom. Over many thousands of years, sediments washed into the lake covered the lake bottom, burying the remains of the mastodon's body. Eventually, the lake filled in almost completely to form a mucky bog, and the mastodon's bones were found in the peat at the bottom. Bones of ancient animals may also be found in solid rock. If the animal's body is buried deeply enough in sediment before its bones begin to decay, all or part of the bone may absorb or even be replaced by dissolved minerals present in the groundwater. If the sediment keeps building over many thousands of years, it may be transformed into solid rock by the pressure of the overlying material. Meanwhile, the bones have become a fossil, more closely resembling stone than bone, sandwiched between rock layers.

By studying fossils and the rock layers from which they came, we can learn a great deal about Ohio's prehistory. Long before the Pleistocene mammals roamed Ohio, and even before the Age of the Dinosaurs, Ohio was the underwater home of strange and primitive sea creatures. The Paleozoic Era extended from 570 million years ago to 245 million years ago. During this tremendous span of time, all or part of Ohio was covered by an inland sea, and the climate was summertime warm year-round.

Much of the life in the ancient sea, and the vast majority of Paleozoic fossils found in Ohio, are creatures classified as invertebrates -- animals that have no backbone or internal skeleton. These animals often have hard outer shells, however, which are resistant to decay and good candidates for eventually becoming fossilized. Many of the invertebrates found in modern seas have ancient ancestors common in Ohio's fossil record. Groups of related animals that populated Ohio's Paleozoic sea include mollusks, such as clams, snails and squids; brachiopods, two-shelled creatures similar to clams; arthropods, including insects, crabs and lobsters; cnidarians, also known as corals; cephalapods, including squids, octopus and the pearly nautilus; bryozoans, tiny "moss animals" that form colonies; and echinoderms, such as starfish, sand dollars and sea urchins.

The long Paleozoic era is divided into seven shorter periods lasting from 30 million years to as many as 67 million years each. By closely studying the composition of the rock layers below the soil, as well as the relative numbers and types of fossil organisms, scientists can determine when the sea receded and dry land emerged, ushering in a new geologic era. Between geologic eras, changes in the sea water from shallow to deep, clear to murky, or salty to fresh, along with changes in climate, signal the dawning of new geologic periods or epochs within an era.

During the Cambrian and Ordovician periods of the Paleozoic era, from 570 million to 438 million years ago, small invertebrates evidently dominated the warm, shallow, salty sea. The limestone rock layer that formed during the Ordovician period, which is covered by as many as 5,000 feet of more recent rock layers elsewhere in the state, was tilted upward by powerful geologic forces millions of years ago, and today is exposed just below the soil in southwest Ohio, near Cincinnati. The Ordovician limestone is studded with well-preserved fossils of the shelled sea creatures. Perhaps the best known of all fossils in Ohio are the trilobites, a class of hard-shelled arthropods that teemed in the Cambrian and Ordovician seas, but was extinct by the close of the Paleozoic era. The vast numbers of good specimens of a variety of invertebrates, and the proximity of the ancient Ordovician limestone rock layer to the surface make southwest Ohio a world-famous destination for fossil collectors.

The deeper, darker seas of the Silurian and Devonian periods, from 438 million to 360 million years ago, saw a new kind of creature rise to prominence. These sleek swimmers were vertebrates, equipped with flexible backbones and complex internal skeletons, as well as rows of teeth for grinding food and external scales for protection. They were able to move quickly through the water over great distances, free from the bulky outer shells of their invertebrate neighbors.

Moving swiftly and noiselessly above the murky sea floor, the scaly giant thrusts itself suddenly upward. From the top of its armor-covered head to the swish of its dorsal fin, the monster measures sixteen feet, and weighs more than a ton. It grasps its unsuspecting prey, a shark, in its spiky jaw and crushes it with sharp cutting blades inside its enormous mouth.

This Devonian "Jaws, " formally known as Dunkleosteus terrelli, was an arthodire, an order of armor plated, predatory fish that is now extinct. Many other fish of the Silurian and Devonian seas succeeded in becoming the ancestors of modern day fish species. Relatively few succeeded in becoming fossils, however. After death, if not eaten by a bigger fish, the soft exteriors of their bodies decayed quickly and their bones separated or deteriorated before they could be encased in sediment. Nevertheless, some complete fish fossils have been found, and they have provided a wealth of information about life in the Silurian and Devonian seas.

Interested in learning more about Ohio's prehistoric past?Fossils of Ohio, the ODNR Division of Geological Survey's Bulletin Number 70, is a fascinating and authoritative resource. This newly revised, 577-page soft-bound book provides text, photographs and identification keys for beginners and experts, alike. Fossils of Ohio costs $18 plus tax and is available from the Geologic Records Center, ODNR Division of Geological Survey, 4383 Fountain Square Court, Bldg. B-2, Columbus, Ohio 43224. There is an additional $3 shipping charge for mail orders.

The final three periods of the Paleozoic era saw the gradual shift from dominance of the sea and its creatures to dominance of land and its creatures. The Mississippian, Pennsylvanian and Permian periods lasted roughly 40 million years each. Fossils recovered from the rock layers deposited during these periods indicate that prehistoric sharks thrived during the Mississippian. Amphibians, animals adapted for breeding in water and adult life on nearby land, flourished in the Pennsylvanian and mark a major transition to a drier Ohio.

During the Pennsylvanian, much of the state was covered with swamps surrounded by grand tree ferns, tall reeds and rushes. As these plants died and slowly decayed in the shallow, murky swamp water, they formed beds of peat. In turn, the peat beds were eventually covered with heavy layers of sediment, and over many thousands of years, were compressed under heat pressure to form coal -- one of Ohio's most important fossil fuels. Strange land dwelling reptiles called pelycosaurs laid their eggs on land during the Permian period. These lizard-like meat-eaters could reach lengths of up to nine feet, and featured skin-covered sails on their backs.

The geologic era following the Paleozoic, called the Mesozoic Era, was the great age of the fantastic reptiles called dinosaurs. The Mesozoic Era lasted 179 million years, from about 245 million years ago to 66.4 million years ago. Although a variety of dinosaurs certainly roamed Ohio, there were no rock layers formed in Ohio during the Mesozoic Era, and hence no dinosaur fossils. By this time in earth's history, Ohio was high and dry, and the sediments that build up to gradually form rock layers were probably being washed away by the forces of wind and water as quickly as they accumulated. At the end of the Mesozoic Era, 66.4 million years ago, dinosaurs had become extinct world-wide.

Ohio's cool climate during the Cenozoic Era, which includes the Pleistocene Epoch, was well suited to the warm blooded mammals that grew in numbers and diversity over 66 million years. Today, the glacial ice is long gone from Ohio, but nearly 40 species of mammals common during the Pleistocene are still Ohio residents. Several other species that once lived in Ohio, including grizzly bear, moose, caribou and tundra musk-ox, have sought refuge in the vast wilderness and cold temperatures of Alaska and northern Canada.

Like a spell-binding mystery novel, the volumes, chapters and pages of Ohio's prehistoric past are written in layer upon layer of stone. Much of the plot is already known, but many thrilling details and surprise twists await future generations armed with hammers, chisels and imagination.