Types of Fossils

A small rock, with an imprint on it, an imprint that can take you millions of years back, even before the evolution of humans...that's what amazing about a fossil. Have you seen the movie Jurassic Park? Did you see the part where the dinosaurs were brought back to life using the dinosaur DNA that the scientists found on the fossil of a mosquito? Amazing what a fossil can really do. I guess you have read in your school books all about the dinosaurs, the different types of dinosaurs, what we mean by fossils, how they are formed, how they helps us to know more about the past, etc. But do you know what are the different types of fossils that can be found in this world today? If not, then here is a brief description.

What are Fossils?

I know that you already know what are fossils, but, before we go into the details, let us just refresh our mind about what we exactly mean by fossils and how do fossils form. The term 'fossil', is a Latin word which when translated into English means, 'Something that has been dug up'. These fossils, as you must be knowing already, are used to study the process of evolution. They are the remains of plants and animals that lived hundreds and million years ago. Not all animals and plants formed fossils, this was because some of the dead plants and animals were either gobbled up by other animals or they just decayed away. In order to turn into a fossil, one had to be buried as fast as possible by sediments. The fossils were formed when, after the death of an animal or plant, layers of sediment starts forming on them and years later when these sediments turns into rocks, it contains the imprint of the dead animal and this is how the fossils are formed.

Different Fossils

Now that we have recalled what are fossils and how they are formed, let us now take a look at the various fossils. There are four main classifications of fossils and each of them have been classified on the basis of their formation.

Mold Fossils
The mold fossils are the fossils which are formed in the substrate, just like the negative impression of an animal or plant. The mold fossils are produced when, by the process of leaching, the shell material is removed in order to leave a gap in the rock, which bears the features of the original shell. Some of the mold fossils retains the complete image of the original plant or animal which was fossilized. These fossils usually forms under water, when the layers of silt builds up over the years and forms stones or rock.

Cast Fossils
Another type of fossils are the cast fossils. Sometimes, when the mold fossils gets filled by some kind of minerals, the minerals, with the passage of time, starts hardening and slowly, they form a replica of the original fossil which was already there. Wondering where the minerals might come from? Well, since most of the mold fossils are formed underwater, some of the minerals might seep in with the water. That's how a cast fossil is formed.

Trace Fossils
The Trace fossils are also known as ichnofossils. This type of fossil tracks the various activities of the animal whose fossil it is. From this kind of a fossil we get to know how the animals hunted, how they walked or how they traveled etc. These trace fossils can either be footprints of the animals, the pathway made by the sea mollusks, and sometimes even the droppings of various animals. When you walk on mud or wet sand or even wet cement, you leave your footprint behind. When this dries up or hardens, they leave a permanent impression which, with years collects layers of soil and sediments and turns into a sedimentary rock. This is same manner in which a trace fossil is formed. There are several types of trace fossils:

• Domichnia
• Fodinichnia
• Pascichnia
• Cubichnia
• Repichnia

True Form Fossils
True form fossils are formed when the animal or plants are trapped within the ice or tree sap or maybe tar, and remains there for years, keeping its original features. The hard parts or the soft tissues do not decay for years and remains as it was when it was fossilized.

Thus, these are the various types of fossils that are found today. These fossils tells us all about the past, and by past I do not mean hundreds or thousands of years back, but millions and millions of years back. If you have or can get hold of any of these fossils, do share your experience with us.