TYPES OF FOSSILS

                                                             TYPES OF FOSSILS 

                                                                 figure 1.2

                                      

TYPE OF FOSSIL:-

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.

                                                               figure 1.3 ( mold fossil )

MOLD FOSSILS

1.     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. They are quite similar to the negative impressions left by an animal or a plant.

2.     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.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 of silt start building up throughout the years, eventually resulting in the production of rocks and stones.

 

                                                figure 1.4 ( cast fossil )

CAST FOSSILS

 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.

                                              figure 1.5 ( trace fossil )

          

Trace Fossils

Dinosaur footprint from old times

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.
 These types include:

·        Coprolites

·        Tracks and trails

·        Gastroliths and burrows

·        Borings.

Tracks and trails refer to animal footprints, for instance, that were initially made of soft sediment after which they later transformed into hard sedimentary rock.

Coprolites are fossils that are formed from the stomach content of organisms as well as their dung. These greatly help in identifying the food and dietary habits of various organisms.

Burrows, on the other hand, are holes made by organisms in rock, wood or sediment. These burrows are later filled with mineral matter found in the underground that helps preserve them for many years to come.

Gastroliths are stomach stones that are basically found in the stomach region of many reptiles, mammals, and birds. These stones were once popularly used to grind food by several extinct reptiles.

 

True Form Fossils:-

There are often times when different plants and animals get trapped or stuck within the ice, tar, or tree sap, and in most cases, they end up being trapped for hundreds of years. As they remain there for years, the substance they’re stuck in ends up keeping their original features and characteristics fully intact and whole.

These features or hard parts remain just the way they began and do not decay or rot for hundreds of thousands of years. Eventually, after being frozen and jammed between these substances, the organisms are found thousands of years later and hold great historical evidence within them.

Unlike mold fossils and cast fossils, true form fossils are not created with the help of an impression but are formed as a result of being displaced by the minerals that eventually hardened to transform into rocks.

 

figure 1.6 ( body fossil )

Body Fossils:-

These are easily the most common and popular types of fossils found all over the world. As the name evidently suggests, body fossils are formed from the remains of dead plants and animals. These are usually hard parts of an organism including shells, bones, teeth, woody trunk, stems, and branches.

The interesting bit about body fossils is that they are found in a variety of different sizes, ranging from tiny living things that can only be looked at with the help of a microscope to massive and gigantic dinosaurs that are highly visible to the naked eye even from far away.

 Whole-body fossils are the complete remains of organisms belonging to the prehistoric times. These also often include the soft tissue of organisms, for example, insects that get trapped inside tree sap and then harden down to create amber.Soft tissue like skin, organs, and muscle usually fall to pieces once the organism dies, leaving behind only the bone skeleton and the hard shells of all those organisms. The most common types of body fossils include teeth, bones, and claws. Bones have by far been the most vital body fossil to learn about dinosaurs

The soft tissues decay and deteriorate soon after the organisms die. Keeping this phenomenon in mind, it is important to note that animals like shrimps and insects that have weak skeletons are less likely to be preserved. Also, those animals that don’t even have a skeleton, to begin with, have very thin and rare chances of being fossilized.

 

                                                             figure 1.7 ( petrified wood )

PETRIFIED FOSSILS:-

Petrifaction is a process in which things turn into stones, and petrified fossils are those that are formed when minerals from the underground replace certain or all parts of numerous organisms.Since water is often fully enriched with dissolved minerals, it easily reaches the dead organisms by seeping through the layers and cracks of rocks or sediments. Once this mineral-rich water evaporates, it leaves behind the stone, hardened materials and minerals.

There are numerous types of petrified fossils, among which petrified wood is the most common type. Another type is teeth and bone, but these are less common as compared to petrified wood mainly because they end up decomposing really quickly and easily.

Petrified fossils have served far greater purposes than just in terms of their importance and value. Scientists have used information from these fossils and found a link to phylogeny, a study of how organisms are connected to evolution.

                                  figure 1.8 ( plant fossil with unusual matrix)

CARBON FILM FOSSILS:-

It is a very common fact that all living organisms contain an element of carbon in their body. So, when a dead organism lays on a rock and is deeply buried inside sediment, a thin layer of this carbon is left behind and deposited onto the rock over the passage of time, and simultaneously, all the material found within the organism gradually breaks down.

 This thin carbon layer basically reveals the respective organism’s delicate parts, for instance, leaves from a plant that probably lived millions of years ago. This happens because the oxygen, hydrogen, and nitrogen disappear from the organism’s body and end up either being dissolved or vaporized under the water body.The whole decay process and the carbon being left behind are called by two common names – carbonization or distillation.

Unlike petrified fossils that create a three-dimensional cast, carbon film fossils create a two-dimensional image that is well-imprinted into the rock or sediment. These films also greatly stand out from the rock since they have a very prominent black or brown color. The most common types of carbon film fossils are leaves, fish and crustaceans, primarily because the specimens that are preserved under the water body are the only ones that leave behind carbon films.

 In the case of leaves in particular, their internal components like cell wall structures and membranes are broken down.However, the cells end up being richly filled by water that is enriched with a lot of minerals. The water then becomes solidified which, in turn, helps preserve the delicate and minuscule features of most of these organisms.

 

                                    figure 1.9 ( preserved fish remains )

   PRESERVED REMAINS:-

The process of fossilization often preserves the whole of an organism; however, there are also times when it preserves only a part of the organism with very little change.

Such organisms are conserved in or very close to their original states. They are the ones that are called preserved remains fossils and are incredibly similar to the true form fossils. Preserved fossils are a very rare occurrence, considering how most fossils end up suffering a great amount of damage due to various processes like sedimentation and weathering way before these fossils are even discovered.

 Fossil preservation happens in two ways, where one is with alteration, and the second type is without alteration. The former is way more common where the original organism is completely or partially changed and then transformed into a whole new material.

 The alteration takes place through the process of carbonization, petrifaction, and re-crystallization. In all these methods, the hard part of the living organic material is substituted with the help of a new mineral.

 On the other hand, preservation without alteration results in the original organic matter remaining intact and completely unchanged. The process through which that happens is called ‘amber.’

 In amber, what really happens is the organic matter, be it an insect or a leaf, gets surrounded by a natural tree resin. Over time, this protective cover or layer preserving the matter hardens and becomes stone-like. Amber is also referred to as a gold-colored resin that originally comes from the pine tree sap.

 Another way of remains being preserved without alteration includes being frozen in ice. Many organisms die in intensely cold regions, after which their bodies are frozen in ice and even something as small as their strands of hair gets preserved in the ice.