Types of Fossils, Five Types of Fossils Considering Finer Aspects as (For CBSE, ICSE, IAS, NET, NRA 2022)

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Types of Fossils

  • Fossils are the remains or traces of ancient life that have been preserved by natural processes.
  • Fossils can be divided into two categories, fossilized body parts (bones, claws, teeth, skin, embryos, etc.) and fossilized traces, called ichno fossils (which are footprints, nests, dung, tooth marks, etc.) , that record the movements and behaviors of the dinosaurs.
  • 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.

About Fossil

  • Fossils, the remains of prehistoric organisms or other evidence of prehistoric life, tell you a great deal about what the world was like millions or even billions of years ago.
  • Imprints, tracks, and trails can also become fossilized, like dinosaur footprints or worm burrows.
  • Five different types of fossils are body fossils, molds and casts, petrifaction fossils, footprints and track ways, and coprolites.
  • These are called trace fossils.
  • In 2017, researchers confirmed that the oldest fossils, which were found in a rock in Western Australia, prove life existed on Earth over 3.5 billion years ago.
  • 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”

Types of Fossils

Types of Fossils
Mold fossilsA fossilized impression made in the substrate; a negative image of the organism.
Cast fossilsFormed when a mold is filled in.
Trace fossils or Ichno fossilsFossilized nests, gastroliths, burrows, footprints, etc.
True form fossilsFossils of the actual animal or animal part.

Five Types of Fossils Considering Finer Aspects As

  • Body Fossils
  • Molecular Fossils
  • Trace Fossils
  • Carbon Fossils
  • Pseudo fossils

Body Fossils – Soft Parts

  • The first type, body fossils, are the fossilized remains of an animal or plant, like bones, shells, and leaves.
  • The most common body fossils found are from the hard parts of the body, including bones, claws, and teeth. More rarely, fossils have been found of softer body tissues.
  • Body fossils include:
    • Bones: these fossils are the main means of learning about dinosaurs. The fossilized bones of a tremendous number of species of dinosaurs have been found since 1818, when the first dinosaur bone was discovered. The was found in 1858 in New Jersey, USA.
    • Teeth and Claws: Sometimes a bit of a broken tooth of a carnivore is found with another dinosaur՚s bones, especially those of herbivores.
    • Eggs, Embryos, and Nests: Fossilized dinosaur eggs were first found in France in 1869. Many fossilized dinosaur eggs have been found, at over 200 sites. Sometimes they have preserved parts of embryos, which can help to match an egg with a species of dinosaur. The embryo also sheds light on dinosaur development. The nests and clutches of eggs tell much about dinosaurs՚ nurturing behavior. A dinosaur egg was found by a 3-year-old child.
    • Skin: Some dinosaurs had thick, bumpy skin, like that of an alligator . A 12-year-old girl discovered a T. rex՚s bumpy skin imprint, confirming that it had a “lightly pebbled skin.”
    • Muscles, Tendons, Organs, and Blood Vessels: These are extremely rare because these soft tissues usually decay before fossilization takes place
    • 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.

Molecular Fossils

  • Molecular fossils are often referred to as biomarkers or bio signatures 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.

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.

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.

Pseudo Fossils

  • 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 pseudo fossils.

How Are Fossils Made?

  • Living things (usually aquatic) die and then get buried quickly under sand, dirt, clay, or ash sediments.
  • 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.
  • Through erosion caused by weather, wind, and water, the fossils become exposed at the surface again.

Ways That Organisms Can Turn into Fossils

Ways That Organisms Can Turn into Fossils
Unaltered preservationLike insects or plant parts trapped in amber, a hardened form of tree sap
Permineralization or petrificationIn 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 per mineralized

ReplacementAn organism՚s hard parts dissolve and are replaced by other minerals.

Like calcite, silica, pyrite, or iron.

Carbonization, coalificationIn which only the carbon remains in the specimen.

Other elements, like hydrogen, oxygen, and nitrogen are removed.

RecrystallizationHard parts either revert to more stable minerals or small crystals turn into larger crystals.
Authigenic preservationMolds and casts of organisms that have been destroyed or dissolved.

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