9 Different Types of Fossils

Did you know that a single preserved bone from ancient civilizations can give you quite an insight about almost the entirety of that particular civilization?

Along with genetics, fossils have proven to be one of the most useful ways to learn about the great history of life on earth. Common examples of fossils include tracks, footprints, bones, teeth, dung, and skin, to name a few.

Simply put, fossils are records of organic matters and organisms that consist of intricate details about their shape, size, and features of the body parts. They are basically conducive to conserving and preserving a variety of different types of organisms.

This has greatly helped scientists, archaeologists, and paleontologist learn a great deal about how the world and life on earth looked like some millions and billions of years ago.

Speaking of which, check out our article explaining about 25 Most Popular Types of Dinosaurs!

Where are Fossils Found?

There is no denying the fact that fossils are found in the Earth’s crust and surface, however, if you were to narrow it down, they are commonly found in all those areas or spaces where sedimentary rocks may be exposed.

These rocks are defined as those that are formed when multiple layers of clay, sand, mud, and silt combine together and then harden over a span of a billion years or so. They harden so much that eventually, they end up adopting a rocky formation, hence the name sedimentary rocks.

How are fossils different to bones? Check out my article here to read the differences between fossil and bone.

These rock-like layers settle down in water bodies like oceans, lakes, and swamps and basically create a kind of a settlement there. This is one of the main reasons why you will notice that most of the fossils found till today are remains of those animals that lived either near the water or in the water.

Types of Fossils

Fossils are remnants or traces of organisms from prehistoric times that belonged to the past geological ages. These traces could be anything from a leaf imprint to the skeletal remains of living organisms that are preserved in the Earth’s crust.

There are different types of fossils, each of which has been incredibly beneficial in telling us about the life on earth that existed billions of years ago.

Mold Fossils

These are fossilized imprints that are made within a substrate. The substrate, in this case, is usually a rock or sediment. The fossil makes use of these substrate components in order to leave their mark on them.

A mold fossil is kind of like an impression that is made in the substrate. They are quite similar to the negative impressions left by an animal or a plant. Mold fossils are primarily formed through a process called ‘leaching.’ In this process, the shell material of rock, for instance, is removed, leaving behind a hollow or gap in the rock.

This rock basically sports some qualities or features of the original shell. Throughout the whole process of leaching, some of these end up retaining the complete image of the original animal or plant.

Unlike cast fossils, mold fossils are more towards the hollow end, which is one of the reasons why the end or resulting image is more like a negative image or impression of the organism’s body part.

In easier or simpler terms, mold fossils are created shells, and other similar structures are buried in sediment, after which they end up being dissolved by the underground water. The resulting mold that is created afterward is a reflection of the surface markings and also the shape of the organism.

The hard part of the organism completely dissolves over time, and all that is left behind is an empty space or area of its body shape. Once dissolved underwater, layers and layers of silt start building up throughout the years, eventually resulting in the production of rocks and stones.

Cast Fossils

These are a result of the mold fossils when the latter gets filled with some kind of minerals. What happens here is that when mold fossils are formed, there are times when their hollowness is filled with certain kinds of minerals.

Over time, these minerals begin to harden, and in doing so, they tend to form an exact replica or model of the original fossil that was there in the first place. This replica is what we call a cast fossil.

In other words, when a plant, animal, or any other organism dies, certain chemical reactions take place in its remains that lead to a deterioration of bones and great flesh decay. Both these things create a gap or hollow in the organism, more like a cavity that is eventually filled up minerals found in the underground.

When these minerals harden over the passage of time, they create a ‘cast’ which is what gave these fossils their respective name. Cast fossils leave an imprint in the rock or sediment and go a single step further than the mold fossils.

So, if you were to draw a comparison of the two, mold fossils take up all the negative space in an organism while cast fossils hold all the positive space. Some examples of cast fossils include embryos, skin, teeth, leaves, etc.

Trace Fossils

These fossils are also called ‘ichnofossils,’ and they contain any potential information or traces left behind by the organism. They are basically glimpses that let us know how the particular organism behaved and what its activities were like when it was alive.

The term ichno’ comes from the Greek word “ikhnos,” which translates to mean ‘trace or track’ in the English Language. Trace fossils are probably the most common types of fossils, and they are more helpful than fossilized body parts in terms of providing us with key information on the organism how it lived, hunted and rested, what it ate, etc.

These fossils are more like indirect evidence of the existence of the prehistoric life. There are different types of trace fossils that can be grouped together into various categories. These types include:

• coprolites
• tracks and trails
• gastroliths and burrows
• borings.