The bodies of insects seem too small and too fragile to survive long enough to be preserved as fossils. But insects also have hard parts, including a tough external skeleton, and given the right set of circumstances even some of the tiniest of them – animals the size of a mosquito – can be preserved as fossils.

Plants and animals from humid tropical forests are rarely preserved because they decay rapidly in these regions. Similarly, fossils from mountainous areas rarely survive due to high rates of erosion.

The fossil record certainly has gaps, mostly because the conditions required to create fossils have been rare ever since life began on Earth. A very small percentage of animals that have lived and died ever became fossils. Thus, many pieces of the puzzle are missing; some will never be found.

Many plants and animals do not become fossils because they decompose or are eaten before they can be fossilized. Organisms decompose quicker when exposed to oxygen. Dead organisms are also more likely to be eaten by scavengers when exposed to the open environment. These sediments cover and thicken around the organism.

Natural casts form when flowing water removes all of the original bone or tissue, leaving just an impression in sediment. Minerals fill in the mold, recreating the original shape of the organism. these are commonly marine invertebrates like shells.

Once fossils are formed, they might be washed away by streams, moved by glaciers, carried by scavengers, or caught in rockslides. Weathering by wind, water, and sun can destroy a fossil by wearing it away.

sedimentary rock

Some examples:

• Track: an impression made by a single foot.
• Trackway: a number of tracks made during a single trip.
• Trail: an impression made by an animal without legs.
• Burrows: a hole or holes an animal dug into loose sediment (like mud).
• Borings: a hole or holes an animal dug into a hard substrate (like wood or rock).

Most trace fossils can be placed into three general categories: tracks and trails, burrows and borings, and gastroliths and coprolites.

James comparing ‘fucoids’ to modern traces made it increasingly clear that most of the specimens identified as fossil fucoids were animal trails and burrows. True fossil fucoids are quite rare.

Trace fossils provide palaeontologists with evidence of the activities of ancient animals – something body fossils simply can’t do. Trace fossils are formed in place and can therefore tell us about the ancient environment in which the animal lived.

Ichnofossils, also known as trace fossils, are geological records of the activities and behaviors of past life. Some examples include rock evidence of nests, burrows, footprints, and scat. These fossils are different from body fossils that preserve the actual remains of a body such as shells or bones.

True form fossils are large body parts of an organism that has been replaced by minerals. True form fossils are formed by a process called petrification. Common examples of these fossils include limbs, torsos, fingers, and heads.

cast fossils (formed when a mold is filled in) trace fossils = ichnofossils (fossilized nests, gastroliths, burrows, footprints, etc.) true form fossils (fossils of the actual animal or animal part).

Many fossils are of shells, bones, or teeth that have been turned to stone by a process called petrification. Some fossilized animals were not turned to stone but simply preserved when they became trapped in amber, tar, peat, or ice.

There are 6 types of fossils. They are body, trace, cast and mold, living, s carbon film, and petrified wood.