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Body Fossils
Body fossils are the fossilized remnants of organisms. The hard parts of organisms, such as bones, teeth and claws are the most common types of body fossils recovered in the fossil record. However, softer body parts, such as muscles, blood vessels and tendons, have rarely been recovered.
Trace Fossils
Trace fossils do not contain any material from the original organism, but are instead a record of the movement or behavior of the animal. Trace fossils can often yield a lot of circumstantial information about an organism. Footprints, for instance, can reveal whether an organism is bi-pedal or quadra-pedal, the length of stride and speed, and the bone structure of the foot. Coprolites can yield information about an organism's eating habits and diet.
Mold and Cast Fossils
A mold fossil is the hollow impression that an organism has made on rock. When the organic material composing the original organism decomposes, it leaves a cavity that resembles the organism. A cast fossil can form in the cavity when it is filled by surrounding sediment and minerals in a process known as authigenic preservation.
Fossilized Organisms
Organisms dating as far back as the early Pre-Cambrian, such as Stromatolites which date back more than two billion years ago, have appeared in the fossil record. Bacteria and Archaea are the earliest organisms to appear in the fossil record, but later on, algae and land plants such as early ferns appear. The marine environment was rich with life before land was widely colonized, and many types of early fish are exhibited in the fossil record, such as the earliest jawless fish dating back to the Cambrian some 500 million years ago. Many land animals appear later in the fossil record, from arthropods such as giant millipedes and dragon flies, to gigantic dinosaurs such as Diplodocus and Tyrannosaurus Rex, to earliest mammals, which appeared during the Cretaceous. Other organisms represented in the fossil record include trilobites, ammonites and graptolites.
Types of Fossil Sediments
Ground fossils and fossil-supported sediments have formed over the ages. Limestones, for instance, are formed from the ground skeletons of tiny marine microorganisms. Chalk is a white porous type of limestone that is formed by the accumulation of calcite plates shed from coccolithophores, tiny marine microorganisms. Sedimentary rocks, such as bindstones and grainstones, are supported, to various extents, by the fossilized remains of marine organisms, generally bivalves, called bioclasts.