Types Of Fossils

Fossils are the remains or traces of ancient life that have been preserved by natural processes. Examples of fossil include shells, bones, stone imprints of animals or microbes, exoskeletons, objects preserved in amber, petrified wood, coal, hair, oil, and DNA remnants. There are five types of fossils:

  1. Body Fossils
  2. Molecular Fossils
  3. Trace Fossils
  4. Carbon Fossils
  5. Pseudofossils

What is a Fossil?

Fossils are the remains or traces of ancient life that have been preserved by natural processes, from spectacular skeletons to tiny seashells. Imprints, tracks and trails can also become fossilised, like dinosaur footprints or worm burrows. These are called trace fossils. Hence, a fossil can be defined as,

A remnant, impression, or trace of an organism of past geologic ages that has been preserved in the earth’s crust

By studying the remains of life and the traces it left behind we can learn a lot about how animals and plants lived and behaved millions of years ago.

What are the Different Types of Fossils?

Fossils represent the remains or traces of once-living organisms. Broadly, the four types of fossils are:

Mold fossils A fossilized impression made in the substrate; a negative image of the organism.
Cast fossils Formed when a mold is filled in.
Trace fossils or Ichnofossils Fossilized nests, gastroliths, burrows, footprints, etc.
True form fossils Fossils of the actual animal or animal part.

Types Of Fossils

The fossils can also be categorised into five categories considering finer aspects as:

1. Body fossils – Soft parts

The first type, body fossils, are the fossilised remains of an animal or plant, like bones, shells and leaves. These can be mould and cast fossils, like most of the fossilised dinosaur skeletons and big bones we see, replacement fossils, like petrified wood, or whole body fossils – mammoths caught in the ice, or insects trapped in amber.

A mold is an imprint left by the shell on the rock that surrounded it. There are two types of molds. They are:

External Mold:

It is a mold of the outside of the shell. Each time we break a shell or bone out of the rock, an external mold is left behind.

Internal Molds:

Molds of the underside of the shell may be left on the surface of rock that formed when sand or mud filled the inside of the shell.

2. Molecular Fossils

Molecular fossils are often referred to as biomarkers or biosignatures and represent products of cellular biosynthesis that are incorporated into sediments and eventually into a rock. Many of these chemicals become altered in known ways and can be stable for billions of years.

3. Trace Fossils

Trace fossils are marks left by an animal or plant that has made an impression. These fossils include nests, burrows, footprints or any other markings of the animal’s time on the earth. The structure of the animal or plant remains as a mineral form. The colours of the minerals that replace the form can be dazzling. Sometimes they are made into art and jewellery.

4. Carbon Fossils

All living things contain an element i.e. carbon. When an organism dies and is buried in sediment, the materials that make the organism break down and eventually only the carbon remains. The thin layer of carbon left behind can show an organism’s delicate parts like leaves or plant e.g. fern fossil 300 million years old.

5. Pseudofossils

Sometimes watery solutions of various minerals speed through the sediments and it takes the shape of some plant part or animal. Their study shows that they are neither plants nor animals. Such fossils are called pseudofossils.


What is Taphonomy?

Taphonomy is a field of palaeontology, paleoanthropology, and archaeology that studies human and animal remains in relation to the post-mortem (after death) transformations that occur in burial sites. From the Greek, ‘taphos’, meaning tomb or grave, and ‘nomy’, meaning classification.

In a broader sense, taphonomy is the study of the processes that lead to fossilization, as well as the stages of transformation of remains through the action of environmental factors. The knowledge gathered by this field is important to forensic science as a tool for the analysis of human remains at old crime scenes, mass graves, and mass disaster areas.

How are Fossils Made?

Living things (usually aquatic) die and then get buried quickly under sand, dirt, clay, or ash sediments. Usually, the soft parts decay, or rot away, leaving the hard parts behind. These are ammonites, one of the most common fossils that are found. As time goes on more and more sediment accumulates.

Pressure, heat, and chemical reaction cause the sediments to harden into a rock called sedimentary rock. Movements in the earth’s crust push the layers of sedimentary rock back up to the higher ground. Finally, through erosion caused by weather, wind, and water, the fossils become exposed at the surface again.

Ways that organisms can turn into fossils:

Steps Explanations
Unaltered preservation
  • Like insects or plant parts trapped in amber, a hardened form of tree sap
Permineralization or petrification
  • In which rock-like minerals seep in slowly and replace the original organic tissues with silica, calcite or pyrite, forming a rock-like fossil
  • It can preserve hard and soft parts.
  • Most bone and wood fossils are permineralized.
Replacement
  • An organism’s hard parts dissolve and are replaced by other minerals. ‘
  • Like calcite, silica, pyrite, or iron.
Carbonization, coalification
  • In which only the carbon remains in the specimen.
  • Other elements, like hydrogen, oxygen, and nitrogen are removed).
Recrystallization
  • Hard parts either revert to more stable minerals or small crystals turn into larger crystals.
Authigenic preservation
  • Molds and casts of organisms that have been destroyed or dissolved.

Frequently Asked Questions (FAQs)

Q1: What is a trace fossil? Give examples.

Ans: Imprints, tracks and trails can also become fossilised and are called Trace fossils. Examples are dinosaur footprints or worm burrows.

Q2: Why studying fossil is important?

Ans: By studying the remains of life and the traces it left behind we can learn about how animals and plants lived and behaved millions of years ago.

Q3: What is Taphonomy?

Ans: Taphonomy is a field of palaeontology, paleoanthropology, and archaeology that studies human and animal remains in relation to the post-mortem (after death) transformations that occur in burial sites

Stay tuned with BYJU’S for more such interesting articles like fossil fuels, the formation of fossils, etc. Also, download BYJU’S – The Learning App for loads of interactive & engaging physics related videos and an unlimited academic assist.

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