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1. INTRODUCTION

One major interesting fact about this topic is that scientists have givenevidences of dinosaurs that lived millions of years ago. But how do scientists learnabout them if they have never seen them?? How do they know about their movementand existence???

1.1. FossilsFossils (from Latin fossus, literally "having been dug up") are the preserved

remains or traces of animals (also known as zoolites), plants, and other organismsfrom the remote past.

2. TYPES OF FOSSILS

Following are the major 5 type of fossils

CASTS AND MOULDS

TRACE

PETRIFIED WOOD

CARBON FILM

AMBER

3. CAST AND MOLD:

The creation of a cast or mold is a commonform of indirect preservation. Most fossils do not

contain actual body parts but are impressions,molds or casts of the original organism. Essentially,a mold fossil forms when the organic matter of theorganism decomposes and leaves a cavity, or mold.Casts form when the cavity fills with sediment orminerals that harden. Occasionally, casts and moldscontain the hard parts of organisms, such as shellsor bones. Picture 3.1 shows one type of Cast andmould

3.1. Definition

Molds and casts are three-dimensional impressions in which the surfacecontours of an organism are preserved. Organisms buried in sediment slowly decompose, leaving a cavity that contains an exact imprint of the organisms' shapeand size. When this hollow space fills with material, this material takes the shape of the mold, forming a cast. Although the fossil may exhibit characteristics of the originalorganism, normally no organic material remains.

Picture 3.1 Cast and Mold Fossil


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Submitted by: Sanjana Shanbhag, FYBSC, Zoology, Roll No 993 Page | 2

3.2. Features

Usually molds and casts exhibit a distinct three-dimensional character.Occasionally, inorganic material replaces the shell of an organism, leaving animpression of the interior surface called an internal mold. When this mold fills withsoluble minerals, it forms an internal cast, called a steinkern, which means "stonecast" in German. According to the Petrified Wood Museum, the most commonsteinkern for plants includes the preserved details of the vascular and cortex tissuewithin the plants' pith (the outside surface cavities of the center stem).

3.3. Benefits

Traces of extinct organisms, such as burrows, shells, plants, trails and tracks,represent a type of fossil mold or cast if the three-dimensional integrity is preserved.Molds and casts that faithfully replicate the external form of an organism providepaleontologists clues about the surface anatomy and behavior of an ancient organism.According to The Petrified Wood Museum, a common fossil mold includes insect wingimpressions. By studying the preserved pleating on the wings, paleontologists identify the insect family.

4. TRACE FOSSILS

4.1. Definition

Trace fossils, also called ichnofossils,(Greek ikhnos "trace, track"), are geologicalrecords of biological activity. Trace fossilsmay beimpressions made on the substrate by anorganism: for example, burrows, borings

(bioerosion), urolites(erosion caused by evacuation of liquid wastes), footprints andfeeding marks, and root cavities. The term in itsbroadest sense also includes the remains of otherorganic material produced by an organism forexample coprolites (fossilized droppings) orchemical markers or sedimentologicalstructures produced by biological means - forexample, stromatolites. Trace fossils contrast with body fossils which are the fossilizedremains of parts of organisms' bodies, usually altered by later chemical activity or

mineralization. Picture 4.1 shows one type of Trace Fossils.Sedimentary structures, for example those produced by empty shells rolling

along the sea floor, are not produced through the behaviour of an organism and notconsidered trace fossils.

The study of traces is called ichnology, which is divided into paleoichnology, orthe study of trace fossils, and neoichnology, the study of modern traces. This science

Picture 4.1 Trace Fossil


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is challenging, as most traces reflect the behaviour not the biological affinity of their makers. As such, trace fossils are categorised into form generabased upon theirappearance and the implied behaviour of their makers.

4.2. Paleoecology

Trace fossils provide us with indirect evidence of

life in the past, such as the footprints, tracks, burrows,borings, and feces left behind by animals, rather thanthe preserved remains of the body of the actual animalitself. Unlike most other fossils, which are producedonly after the death of the organism concerned, tracefossils provide us with a record of the activity of anorganism during its lifetime. Picture 4.2 shows a typeof paleoecology.

Trace fossils are formed by organisms

performing the functions of their everyday life, such as walking, crawling, burrowing,boring, or feeding. Tetrapod footprints, worm trails and the burrows made by clamsand arthropods are all trace fossils.

Perhaps the most spectacular trace fossils are the huge, three-toed footprintsproduced by dinosaurs and related archosaurs. These imprints give scientists clues asto how these animals lived.

4.3. Paleoenvironment

Eubrontes, a dinosaur footprint in the Lower Jurassic Moenave Formation at the St. George DinosaurDiscovery Site at Johnson Farm, southwesternUtah.Picture 4.3 shows sample of paleoenviroment.

Fossil footprints made by tetrapod vertebratesare difficult to identify to a particular species of animal,but they can provide valuable information such as thespeed, weight, and behavior of the organism that madethem. Such trace fossils are formed when amphibians,reptiles, mammals or birds walked across soft (probably wet) mud or sand which later hardened sufficiently to

retain the impressions before the next layer of sedimentwas deposited. Some fossils can even provide details of how wet the sand was whenthey were being produced, and hence allow estimation of paleo-wind directions.

Assemblages of trace fossils occur at certain water depths,[1] and can alsoreflect the salinity and turbidity of the water column.

Picture 4.2 Paleoecology

Picture 4.3 Paleoenvironment


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4.4. Stratigraphic correlation

Some trace fossils can be used as local index fossils, todate the rocks in which they are found, such as the burrowArenicolites franconicus which occurs only in a 4 cm (1.6")layer of the Triassic Muschelkalk epoch, throughout wide

areas in southern Germany. The base of the Cambrian period is defined by the first

appearance of the trace fossil Treptichnus pedum. Picture 4.4shows an example of Stratigraphic correlation.

Trace fossils have a further utility as many appearbefore the organism thought to create them, extending theirstratigraphic range.

5. PETRIFIED WOOD

Petrified wood (from the Greek root petro meaning "rock" or "stone"; literally "wood turned into stone") is the name given to a special type of fossilized remains of terrestrial vegetation. It is the result of a tree having turned completely into stone by the process of permineralization. All the organic materials have been replaced withminerals (mostly a silicate, such as quartz) , while retaining the original structure of the wood. Unlike other types of fossils which are typically impressions orcompressions, petrified wood is a threedimensional representation of the original organicmaterial. Picture 5.1 shows a sample of petrifiedwood.

The petrifaction process occursunderground, when wood becomes buried undersediment and is initially preserved due to a lack of oxygen which inhibits aerobic decomposition.Mineral-laden water flowing through the sedimentdeposits minerals in the plant's cells.and as theplant's lignin and cellulose decay, a stone mouldforms in its place.

In general, wood takes less than 100 years to petrify. The organic matter needs

to become petrified before it decomposes completely.A forest where the wood haspetrified becomes known as a Petrified Forest

6. CARBON FILM

Carbon films are a type of fossil, or preservation. They are thin film coatingswhich consist predominantly of the chemical element carbon, which include plasmapolymer films, amorphous carbon films (diamond-like carbon, DLC), CVD diamond

Picture 4.4 Stratigraphic Corelation

Picture 5.1 Petrified Wood
http://en.wikipedia.org/wiki/Permineralizationhttp://en.wikipedia.org/wiki/Organic_lifehttp://en.wikipedia.org/wiki/Mineralhttp://en.wikipedia.org/wiki/Silicatehttp://en.wikipedia.org/wiki/Quartzhttp://en.wikipedia.org/wiki/Petrifactionhttp://en.wikipedia.org/wiki/Petrified_Foresthttp://en.wikipedia.org/wiki/Thin_filmhttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Plasma_polymerizationhttp://en.wikipedia.org/wiki/Plasma_polymerizationhttp://en.wikipedia.org/wiki/Amorphous_carbonhttp://en.wikipedia.org/wiki/Diamond-like_carbonhttp://en.wikipedia.org/wiki/CVD_diamondhttp://en.wikipedia.org/wiki/CVD_diamondhttp://en.wikipedia.org/wiki/Diamond-like_carbonhttp://en.wikipedia.org/wiki/Amorphous_carbonhttp://en.wikipedia.org/wiki/Plasma_polymerizationhttp://en.wikipedia.org/wiki/Plasma_polymerizationhttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Thin_filmhttp://en.wikipedia.org/wiki/Petrified_Foresthttp://en.wikipedia.org/wiki/Petrifactionhttp://en.wikipedia.org/wiki/Quartzhttp://en.wikipedia.org/wiki/Silicatehttp://en.wikipedia.org/wiki/Mineralhttp://en.wikipedia.org/wiki/Organic_lifehttp://en.wikipedia.org/wiki/Permineralization


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films as well as graphite films. The tissue of organisms are made of compounds thatcontain carbon. Following Pic 6.1 shpws carbon film formed on a surface

Sometime fossils contain only carbon. Fossils usually form when sedimentsbury a dead organism. As sediment piles up, the organism's remains are subjected topressure and heat. These conditions force gases and liquids from the body. A thin filmof carbon residue is left, forming a silhouette of the original organism called a carbonfilm

6.1. Formation of Carbon Film

Every living thing contains carbon. When an organism dies or a leaf falls, itsinks into the earth's layers and decomposes. A carbon film is made when the oxygen,hydrogen and nitrogen of the organism disappear, leaving a thin layer of carbon. Thisprocess is known as distillation or carbonization. If the layer of carbon is on a viablesurface, usually under a body of water, an imprint of the organism will remain.

Carbon film fossils are usually black, dark brown or light brown in color,depending on the type of rock they are pressed upon. Unlike trace fossils, molds andcasts, which form a three-dimensional shape of the object or organism, carbon filmfossils are two-dimensional, like a drawing. They preserve an enormous amount of detail, such as the leaves and veins of a plant. Sometimes cells of the plant are evenvisible if the cells were filled with water.

6.2. Organisms

Carbon film fossils normally depict fish, crustaceans and plants. When the fishor crustaceans died, their bodies most likely sank to bottom of the body of water, were

carried by the current and got wedged between or under rocks. This preserved theirbodies from prey and destruction by the current. The plants preserved are commonly water-dwelling

6.3. Carbon Dating

Due to the presence of carbon-14, carbon film fossils are relatively easy forscientists to date. Plants absorb carbon-14 from the air, and animals consume it whenthey eat plant life. At the moment of a plant or animal's death, the carbon-14 begins to

Picture 6.1 Carbon Film
http://en.wikipedia.org/wiki/Graphitehttp://en.wikipedia.org/wiki/Graphite


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decay. The half-life, or amount of time it takes for the number of atoms in any givensample to be reduced by half, is 5,700 years. Scientists are able to test the remainingcarbon-14 in the carbon film fossil to determine its age.

7. AMBER

Amber is fossilized tree resin(not sap), which has been appreciated for its colorand natural beauty since Neolithic times.Amber is used as an ingredient in perfumes,as a healing agent in folk medicine, and as jewelry. There are five classes of amber,defined on the basis of their chemical constituents. Because it originates as a soft,sticky tree resin, amber sometimes contains animal and plant material as inclusions.Amber occurring in coal seams is also called resinite, and the term ambrite is appliedto that found specifically within New Zealand coal seams.

7.1. Formation

Molecular polymerization, resulting from highpressures and temperatures produced by overlyingsediment, transforms the resin first into copal. Sustained heat and pressure drives off terpenes andresults in the formation of amber. Picture 7.1 showsa sample of amber.

7.2. Botanical origin

Fossil resins from Europe fall into twocategories, the famous Baltic ambers and another that resembles the Agathis group.Fossil resins from the Americas and Africa are closely related to the modern genusHymenaea. While Baltic ambers are thought to be fossil resins from Sciadopityaceaefamily plants used to live in north Europe.

7.3. Inclusions

The abnormal development of resin has been called succinosis. Impurities arequite often present, especially when the resin dropped on to the ground, so that thematerial may be useless except for varnish-making, whence the impure amber iscalled firniss. Enclosures of pyrites may give a bluish color to amber. The so-calledblack amber is only a kind of jet. Bony amber owes its cloudy opacity to minutebubbles in the interior of the resin.

In darkly clouded and even opaque amber, inclusions can be imaged usinghigh-energy, high-contrast, high-resolution X-rays.

8. Reference:

1. Google searches2. Fossils Encyclopedia

Picture 7.1 Amber
http://en.wikipedia.org/wiki/Copalhttp://en.wikipedia.org/wiki/Agathishttp://en.wikipedia.org/wiki/Hymenaeahttp://en.wikipedia.org/wiki/Sciadopityshttp://en.wikipedia.org/wiki/Pyriteshttp://en.wikipedia.org/wiki/Jet_(lignite)http://en.wikipedia.org/wiki/X-rayhttp://en.wikipedia.org/wiki/X-rayhttp://en.wikipedia.org/wiki/Jet_(lignite)http://en.wikipedia.org/wiki/Pyriteshttp://en.wikipedia.org/wiki/Sciadopityshttp://en.wikipedia.org/wiki/Hymenaeahttp://en.wikipedia.org/wiki/Agathishttp://en.wikipedia.org/wiki/Copal

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