A fossil is a remnant, impression, or trace of an organism that has lived in a past geologic time. Many fossils have been preserved in fine-grained sedimentary rock, such as limestone and shale. The most common fossils found are plants and animals that once lived in shallow-warm seas or lakes. Fossilization is rare, but occasionally after an organism dies, the soft parts decompose and leave only hard parts, such as shells, teeth, bones, or wood behind. After many thousands of years of being buried in layers of sediment, they gradually turn to stone. Be sure to click on the individual photos to enlarge for better quality viewing.
Algae: Time (Precambrian to Present)
Part of the stromatolite group, this genus of algae (Collenia) has a conical to cylindrical structure composed of limestone and/or silica (quartz). This type of structure is always layered, sometimes with alternating light and dark bands. The minute algal threads of which it is composed can be seen under the microscope. These threads bound together detrital sands and muds in a bed of lime produced by the algae. Like living stromatolitic algae, Collenia inhabited tropical intertidal zones. As algae released oxygen into the atmosphere, they were responsible for a critical change in atmospheric composition during the Precambrian Period.
Ammonite: Time (Devonian to Late Cretaceous)
Ammonites had a series of internal chambers that permitted them to control their own buoyancy. All of the chambers were connected by a central stem called the siphuncle. Most were good swimmers and were scavengers, carnivores, or both. Ammonites are distinguished by the patterns that form their sutures -- the seams between their chambers. The sutures preserved are highly complex, often appearing fern-like. Some ammonites, such as this one have prominent ornamental ribs. The squid-like animal that lived within the shell resided in the last whorl (aperture -- opening). This particular fossil has been beautifully opalized and pyritized.
Asteroid: Time (Ordovician to Present)
Popularly called starfish, asteroids are a group of echinoderms recorded as far back as the Ordovician. Their bodies have relatively little calcified material in its makeup, so entire examples preserved as fossils are very rarely found. These marine creatures are characterized by their hard, spiny covering or skin and their five-fold radial symmetry. Today, many starfish species are brightly colored in various shades of red and orange, while others are blue, gray, or brown. Most modern ones can regenerate damaged parts or lost arms, and they can shed arms as a means of defense.
Bivalve: Time (Mid Cambrian to Present)
Bivalves are composed of two valves connected by a hinge of organic material. Generally, the valves have interlocking teeth along the line of the hinge. Unlike the brachiopods, the valves of these animals are not symmetrical and they lack a pedicle hole. There are many different types of bivalves and they are all classified by their hinges. Most bivalves are filter feeders. Many burrow themselves into the sediment, rock, or wood, while others attach themselves to the seafloor with their fleshy, muscular foot. Bivalves includes clams, scallops, oysters, mussels and many more shell-type organisms. Bivalves inhabit both marine and freshwater habitats, but more than 80% live within the oceans.
Blastoid: Time (Mid Ordovician to Late Permian)
Blastoids are an extinct taxon of echinoderms that reached their greatest diversity during the Mississippian Period. They were sedentary animals that lived most of their lives attached to the seafloor of warm shallow waters. The body region (calyx) of blastoids consisted of three circles of five plates made of calcium carbonate and were shaped like a rosebud. Many blastoid species, such as Pentremites, are useful as index fossils. In life, blastoids were very similar to crinoids. They too had flexible stems made up of stacked disc-shaped plates, a holdfast, and brachioles (arms).
Brachiopod: Time (Cambrian to Present)
Brachiopods are one of the most abundant fossils found on Earth. More than 35,000 species are known and more are being discovered every year. Brachiopods are bottom-feeding marine animals composed of two shells or valves. Viewed from above, their shells appear symmetrical. Most of the fossils have a small hole preserved at the central tip of the bottom valve. Emerged from this region, a fleshy stalk called a pedicle attached itself to the seafloor. The fossil in this photo is of the "butterfly shell" type called spirifers.
Bryozoan: Time (Ordovician to Present)
Bryozoans first appeared during the Ordovician Period. With more than 4,000 species living today, they come in a wide variety of shapes and sizes. Fossilized bryozoans resemble miniature corals, so they can be easily confused with them. Ancient bryozoans thrived in warm, shallow seas. They made their skeletons by secretimg calcium carbonate (calcite), and each individual formed connections with its neighbors. These unique organisms grew and lived as freestanding colonies or sheet-like encrustations on stones or other shells. Some had complex fronds while others had lace-like sheet structures.
Coprolite: Time (Precambrian to Present)
Coprolite is the scientific name for "fossilized dung." That's right; they are classified as "trace fossils" as opposed to "body fossils". Much of the original composition of coprolites has been replaced by mineral deposits such as calcite and quartz. By studying coprolites, paleontologists can tell a lot about the animal's diet, size, migratory patterns, diseases, and predator-prey relationships. Coprolites vary in size ranging from a half inch to sometimes over 23 inches in length. The oldest known coprolite is about 1.9 billion years old. Wow, coprolite happens!
Coral: Time (Ordovician to Present)
Corals are found mainly in the branching form (photo). They are marine animals that secrete calcareous (calcite) skeletons. Each individual in the colony forms its own living space called a calice. These calices can be circular, polygonal, or elongate. Through geologic time, corals have formed extensive limestone deposits and reefs. Corals may be mistaken for bryozoans or sponges. Rugose coral forms resemble the autumn harvest horns while Colpophyllia specimens look similar to a brain, thus are informally called "brain coral". Today corals live in warm, shallow seas and build massive reefs to house a variety of marine organisms.
Crinoid: Time (Ordovician to Present)
Crinoids are a group of echinoderms that possessed a cup-shaped body (calyx) and five or more feathery arms. The calyx rested upon a flexible stem that grew on top of a root-like system called a "holdfast". The crinoid lived by attaching itself to the floor of the warm, shallow seas and collecting plankton with its feathery arms. If the water became too sediment-rich and murky, it would simply detach itself from the sea floor and drift along with the currents to a better location. The cup and the stem tend to fall apart after death, so crinoid fossils are found mostly with the stems and arms.
Cystoid: Time (Cambrian to Late Devonian)
Cystoids are an extinct group of echinoderms. They bare a strikingly similar appearance to crinoids but lack the crinoids' "true arms". As filter feeders, they trapped microplankton in the water by using their short limbs called brachioles. Like the blastoids and crinoids, they anchored themselves to the seafloor; however, they did so by wrapping their short, tapering stems around any convenient fixed object. Cystoid are useful as index fossils for the Ordovician and Devonian Periods. Note that organisms within a certain species that have short geologic ranges make the best index fossils for identifying the age of rocks.
Graptolite: Time (Cambrian to Mississippian)
Graptolites were a small group of aquatic, colonial organisms that first appeared during the Cambrian Period. Their outer-coverings were made of material very similar to our fingernails with no mineralized hard parts. Graptolites are most commonly preserved as carbonaceous (calcite-rich) impressions on black shale. They can also be found in limestone rocks too. They had one or more branches and sometimes are mistaken as fossil plants rather than animals. They have undergone extensive evolutionary changes and are now very useful as index fossils for identifying certain-aged rocks.
Gastrolith: Time (Triassic to Late Cretaceous)
Also known as "stomach stones", gastroliths are rocks which have been detained in the digestive tract of an animal. Gastroliths have been found in some of the plant-eating dinosaurs of the Mesozoic Era. Plant-eating dinosaurs (herbivores) had to constantly feed on vegetation, such as bushes, roots, trees, leaves and branches, in order to grow large and to consume enough nutrients from the poorly nutritious vegetation. Many of the sauropod dinosaurs, such as Brachiosaurus had peg-like teeth which prevented them from chewing. Instead, they had to swallow their food whole and depend upon the stones within their stomachs to grind and chern the leaf and plant matter to a green, watery mixture.
Gastropod: Time (Cambrian to Present)
Appearing during the Cambrian Period and continuing on to the present time, gastropods have become very successful mollusks. With over 60,000 living species, gastropods (also known as snails) inhabit marine, freshwater, and terrestrial environments. Today, living gastropods have a head, eyes, and mouth, and they crawl about on the surface of the land or on the floor of a lake or sea with an enlarged foot. Such soft material disappears during fossilization, so classification is based on the shell characteristics. Gastropods have a single, asymmetric shell composed mostly of aragonite. Each coiled shell consists of stepped whorls which were used for protection against wave currents and predators.
Lycopod: Time (Late Silurian to Late Permian)
Also known as "club mosses", Lycopod trees were vascular plants that were most abundant during the Pennsylvanian (Late Carboniferous Period). Modern club mosses are relatively small, herbaceous plants, but during the Pennsylvanian Period they were the size of large trees. They had dense foliage and their spores contained cones. Many of the fossil lycopod trees measure up to 3 feet in diameter. The trees and their root-systems grew extensively in hot, wet, swampland regions. Lycopod trees are major contributors to the organic material that eventually would become coal. Unlike modern trees, the leaves grew out of the entire surface of the trunk and branches. The bark of the fossilized trees have diamond-shaped leaf scars that are in rows that spiral around the tree trunk.
Nautiloid: Time (Late Cambrian to Present)
Nautiloids are among the group of animals called cephalopods which include ammonites, belemnites, and modern coleoids such as octopus and squid. Nautiloids are often found as fossils in rocks of the Paleozoic age. The shells of the nautiloids may either be straight, such as Orthoceras and curved-coiled, or rarely in a helical coil. Some species from the late Paleozoic and early Mesozoic are ornamented with spines and ribs, but most have a smooth shells. Their shells are composed of aragonite, although through the process of recrystallization, the fossil chambers may be altered to calcite. Specimens of the Ordovician nautiloids, such as Endoeceras have been found to measure up to 13 feet in length.
Ophiuroid: Time (Ordovician to Present)
Although ophiuroids "brittle stars" look very similar to starfish, they are more closely related to the echinoids. Brittle stars have flat, disk-like bodies with five flexible arms different in structure to those of the asteroids (starfish). Moderns ones found today are in huge masses on the seafloor, and fossil remains suggest that the same was true for their early ancestors. In areas with strong currents, brittle stars use their arms to link to each other, and other arms to capture their food. Since their arms are long and fragile, it is rare to find complete fossilized specimens. Photo shows both brittle stars and trilobites.
Orthoceras: Time (Ordovician to Devonian)
Orthoceras is a genus of an extinct nautiloid cephalopod. Their fossils are common and have a global distribution occurring in any marine rock, especially limestone. Their slender, elongated shells have a middle body chamber which progressively becomes smaller with the shell. They also have a tube-like structure called a siphuncle that runs along the subcentral region. They were invertebrates that ranged in size from less than a half inch to 14 feet long. Orthoceras organisms were among the most advanced invertebrates of their time. They had eyes, jaws, and a sophisticated nervous system, and they swam freely by using a "jet propulsion" by squirting water from their bodies.
Sea Urchin: Time (Ordovician to Recent)
Scientifically known as Echinoids, sea urchins and sand dollars are a group of echinoderms that have rigid, globular skeletal structure made of thin calcite plates. Many of them also have spines made of calcite which are attached to the body by a ball-and-socket arrangement. As today, in modern echinoids, the spines were used in defense, and in some cases, walking. Some echinoids, like the sea urchins, were bottom feeders foraging on the sea bed, while others tended to burrow into soft silt layers. The spines of all echinoids are generally found fossilized separately. Today, sea urchins are commonly found across the ocean floors worldwide but rarely in the colder regions. They are commonly found on the rocky ocean floor in both shallow and deeper water and are found often on coral reefs. They eat both plants and animals.
Seed Fern: Time (Devonian to Late Cretaceous)
Seed ferns first appeared during the late Devonian Period and were widespread near the end of the Paleozoic Era. They continued on into the Mesozoic Era but became extinct at the end of the Cretaceous Period. Seed ferns were small trees with the obvious fern-like leaves. Although the foliage resembled that of modern ferns, they reproduced by means of seeds. Modern ferns reproduce by means of spores. Relatively small, some could reach up to 25 feet in height. This photo shows the "part" and "counterpart" fossil of a seed fern. The plant fossils create planes of weakness within the nodules, which tend to split open so that one half (right half of nodule) reveals the upper surface of the plant, while the other half contains an impression (left half of nodule) of the upper surface.
Sponge: Time (Cambrian to Present)
Sponges have been around since the Cambrian Period onward, and because of their success in adapting to their environments, they reached their highest peak during the Cretaceous Period. Sponges are animals called filter-feeders. They feed by filtering nutrients from ocean water. Like this fossilized "glass sponge" called Hydnoceras, several classes of sponges became extinct. Modern (living) sponges have evolved from their early ancestors and have changed very little since their time. The skeletons of "glass sponges" are composed of tiny, needle-like projections of silica (quartz) in a mesh-like network. Such projections would have certainly discouraged predators from feeding on such sponges. Fossilized sponges can be mistaken for corals, but the surfaces of sponges have a great deal of coarse ornamentation and their walls tend to be thicker. The main opening of the sponge would have been at the top and the more narrow bottom section would have been attached to the sea bed.
Trilobite: Time (Cambrian to Permian)
Now extinct, trilobites belonged to the a highly successful group of living organisms called arthropods. They first appeared during the Cambrian Period which is often referred to as the "Cambrian Explosion". A few different species survived up until the Permian Period. Trilobites had an external skeleton (exoskeleton) which was composed of material similar to the shells of modern beetles. Many trilobites had compound eyes while some of them were eyeless. Their sizes ranged from a fraction of an inch to 18 inches in length. These unique creatures thrived within the warm-shallow seas of their time. They are easily recognized by their distinctive three-segment form (cephalon, thorax, and pygidium) and their three lobes (left pleural lobe, axial lobe, and right pleural lobe). When in danger, trilobites could roll themselves up for protection and "play dead". Some were bottom dwellers while others swam about freely in the water or floated near the top along gentle water currents. Trilobites were also able to break free from their exoskeletons for molting purposes and escaping predators.