Paleontology

The word paleontology is the combination of three Greek words,

“Paleo” means “ancient”

“Ontos” means “life”

“Logos” means “to study”

 Paleontology is the branch of geology which concerned with the study of fossils.

The word fossil is derived from Latin word Fossilum which means any thing which is dug out.

Generally the term fossil is used for those ancient remains of living things which are preserved in sedimentary rocks. The minimum time required to fossilize any organism is 1000 years.

SIGNIFICANCE OF FOSSILS:

1-     The fossils are used to determine the age of earth.

2-     They are significant to formulate the geologic time scale.

3-     The continents of fossils preserved in rocks helps to determine the age of that rock.

4-     Fossils show the association with fossil fuel.

5-     Fossils provide us the knowledge about organisms which lived in past, their mode of life, biodiversity, similarities and dissimilarities.

6-     They help in the reconstruction of paleogeography of the earth.

7-     They help in paleoenvironment.

8-     Fossils study provides the evidences in favor of organic evolution and migration of organisms through ages.

There are two sub branches of paleontology, which are “paleozoology” which is concerned with the fossils of animals which are called Fauna, and paleobotony which deals with plant fossils, which are called Flora.

There are two types of fossils, which are

1-     Body fossils

Those fossils in which whole body of any organism is fossilized are called body fossils.

2-     Trace fossils

Trace fossils are those fossils in which traces of organisms are found. They are further divided into two types:-

Tracks: They are made by the feet of animals such as dinosaurs, which were preserved in rocks.

Trails: these traces were made by reptiles which after that preserved in rocks.

CONDITIONS FOR FOSSILIZATION:

There are three most important conditions necessary for any organism to be fossilized, which are:

1-     The organism must have hard parts in there bodies, such as stem or bones.

2-     The organism should buried deep quick after its death.

3-     A suitable environment is needed. Marine environment is most favorable environment for fossilization.

TYPES OF FOSSILIZATION:

There are three ways by which any organism fossilized.

1-     Perminerallization:

In this way of fossilization the body of organism is replaced by minerals.

2-     Replacement/ recrystallization:

In this type the body of organism is replaced by rock forming minerals.

3-     Petrifaction:

In this type of fossilization the whole body of organism is converted in fossils.

PROCESSES OF FOSSILIZATION:

In the process of fossilization preservation of organic remains is a necessity, and this depends chiefly, though not entirely, upon two requisites: 1- quick burial in protective medium and 2- some kind of hard parts, such as a shell or skeleton.

Any condition unfavorable of life of bacteria hinders decay. Decomposition may be retarded or prevented by burial in soft mud of volcanic ash, by low temperatures or very dray air, by sea water, or by a covering of tar or resin.

Since preservation by a protective covering is of first importance in the process of fossilization, animals and plants which live in water have a much better chance of becoming fossils than terrestrial organisms. It is not surprising, therefore, that marine animals are much more common as fossils than those which lived on land.

TYPES OF PRESERVATION:

Unaltered soft parts:

If bacteria are excluded entirely from organisms, their soft parts as well as skeletal structures may be preserved. The best known example of complete preservation is remains of mammoths and rhinoceroses in the frozen tundra of Siberia. Natural mummies have been formed by the dry air of deserts preserving some of the soft tissues and the hard parts.

Unaltered hard parts:

Most invertebrates possess hard parts composed of calcium carbonate, calcium phosphate, silica, complex organic compounds.

          Many shells and skeletons have been preserved in the rocks with no recognizable change except for removal of the less stable organic matter. Examples are abundant shells of Cenozoic mollusks or Paleozoic brachiopods, which retain their original microstructure. Hard parts of insects have been preserved perfectly in amber (fossil resin), in Oligocene rocks of the Baltic region, and in cretaceous rocks of Manitoba.

ALTERED HARD PARTS:

Many fossils show varying degrees of alteration of their original structure. Such changes may effect physically or chemically or both. They may consist only of slight rearrangement of molecules or involve hardly noticeable removals, addition or substitutions.

             There are various processes by which hard parts of any organism are altered. Which are:

Carbonization:

Solutions and other chemical action under water commonly transform the composition of the tissues of the plants and animals to a thin film of carbon. The organic remains then carbonized and the process is called carbonization.

Permineralization:

Shells and bones which are somewhat porous may be made more dense by the deposition of mineral substances by ground water. Hard parts altered in this way are permineralized, and the process is called Permineralization.

Recrystallization:

In this process the original microstructure of organism is lost and shell is converted into a mosaic of interlocking crystals. This occurs as the internal physical structure of some shells is changed by shuffling of molecules as the result of solution and repercipitation.

TRACES OF ANIMALS

Molds and Casts:

Following the burial of the hard parts of an organism sedimentary materials are packed closely around them and if there are cavities, these commonly are also filled by sediments. The impression of skeletal remains in adjoining rock constituents is called a mold. A mold is termed as external mold if the shape of the outer sides of the hard parts. A mold is said to be internal if the impression reveals the form and marking of inner surface.

            Many shells and skeletons buried in sediments are removed by solutions. Where skeletal parts are thus removed the matrix, natural molds can be observed. Filling of the cavity by mineral matter or other substances form a cast.

Impressions:

An impression contains no actual plant material. It is merely the form of say a leaf with its outline and its veins impressed upon a bedding plane of very fine clay as slit. The famous clay pits at per year tenrassive yield Eocene plant remains which are preserved in this way.

                                        PHYLUM BRACHIOPODA

One of the chief divisions of invertebrate fossils consists of the brachiopods. They are marine invertebrates in which the soft parts are enclosed by two deposits of shell, termed as valves. The brachiopods are chiefly inhabitants of the shallow sea bottom. No brachiopods are known to have lived in fresh water. Two main classes of brachiopods are recognized, which are articulata having valves held together without hingement, and inarticulata having valves which bear teeth and sockets for articulation along edges hinged together.

               Following are the orders of brachiopods:

1- Orthida                                           2- Strophomenida                         3- Pentamerida

4- Rhynchonellida                               5- Spirifirida                                  6- Terebratulida       

Symmetry and orientation:

Small brachial valve or dorsal valve, occupies a dorsal position with respect to the animal.

Large pedicle valve or ventral valve, have ventral position with respect to the animal.

Morphological terms:

Beak: Initial point for the growth of valve.

Commisure plane: Line of junction between two valves, straight or wavy.

Inter area (Dethyrium): Plate of curved surface of a valve between the beak and hinge line typically bears the triangular or circular pedicle opening.

Fold and Sulcus: Brachiopod shell bears an anticline appearance in the brachial valve of the Sulcus syncline appearance in the pedicle valve.

Costae and pelica: Radial ridges originating from beak on the valve exterior. Pelica are also radial ridges visible on both valves exterior and interior.

 Hinge:

Knob like protrusion on pedicle valve fits into small depression on the brachial valve, called hinge.

Aductor scars:

These are marks and attachment sites of valve for closing the muscles.

Diductor Scars:

The marks and attachment sites of valve for the opening of muscle are called diductor scars.

PHYLUM MOLLUSCA

Mollusca comprise organisms so apparently different from each other that one would hardly guess their common kinship.

             Snails, slugs, cockles and host of other forms, living and fossils, all are united in this second largest phylum after arthropoda. About 80,000 living and 35,000 fossil spicies cover a huge range of habitates from deep seas, fresh water to th ehighest mountain tops. They are borrowers, filter feeders and predaters ranging  in size from a minute plankton to the largest invertibrate known which is gaint squid.

       There are various classes of phylum mollusca among which three are as following:

Gastropoda: (from cambrian to recent)

Cephalopoda: (upper cambrian to recent)

Pelcypoda: (ordovician)

Gastropoda:

They include animals which bear a coiled or uncoilled calcareous shells, and other has no hard parts. They are marine as well as fresh water and also terresterial. The shells of gastropods is univalve.

Morphological features:

Whorl: Individual coil is called whorl.

Spire: collectively whorls called spire.

Suture: the whorls lies in mutual contact by a line is called suture.

Collumela: Inner faces of the whorl united togather by a solid pillars is called collumela.

Umblicus: The cavity open at the base of the shell is called umblicus.

PHYLUM ARTHROPODA

Animals belong to this phylum are called arthropods ( “arthro”, means jointed and “pod” means foot) are invertebrates of highly varied forms, distinguished primerily by a segmented orgnization of the body and the possession of a hardened external covering called exoskeleton. It comprises of about 700,000 spcies.

            There are five main classes belong to this phylum, which are

1-     Insecta: Comprising the multitudinous host of insects.

2-     Chelicerata: It includes spiders, scorpions, ticks and mites.

3-     Myriapoda: Comprises of centipeds and milipeds.

4-     Crustacea: It contains lobsters, crabs, shrimps, crayfishes, ostracodes, and barnacles.

5-     Trilobutomorpha: It is the most important class of arthropods from geological point of veiw, its spcies are extincted. The animals belong to this class are called trilobites.

INTRODUCTION OF CLASS TRILOBITOMORPHA:

Tri = three/ Lobe = part / Morph = shape

This class was the chief representative of arthropods in the lower palaeozoic, and extinct in permian. The growth of the trilobites was the frist massive radiation  of arthropods into the marine environment, where they lived mostly in fairly shallow water crawling and grubbing along the bottom. The great majority lived this kind of benthic existence, although a few are known to have been free swimming or nektic. And although most trilobotes were less then 10 cm long, some have been discovered which were almost 70 cm from end to end. They are without doubt the most important fossils arthropods.

Morphology of trilobites:

From the word trilobitos it is clear that animal had three lobe construction. The body of trilobites is divided into three parts, the exterior one is called cephalon, and then comes thorax, which is the part have three axial lobes and the posterior one is called pygidium.

Cepholon:

It is the one of the most important part of trilobites, because the features of this parts are very useful during classification. Structure of cephalon are particularly concerned in ontogenetic development, and influenced by evolutionary trends.

Facial sutures: The cephalon of all trilobites, except the group called agnostida, is divided into structurally distinct elements by curved lines of partitions called facial sutures. The facial sutures of most trilobites are partly on the dorsal side of the cephalon, but may be restricted to the lateral and anterior mrgins, which is bounded laterally and anteriorly by the facial sutures,is termed the cranidium.

             The parts of the head shield which separate from the cranidium at the time of molting are known as free cheeks. Trilobites have doubler marginal sutures as a permitive feature are classed as protoparian, and those in which the marginal position of the sutures is interpreted to signify evolutionary specialization are called hypoparian. If the sutures anteriorly may run obliquely outward to the edge of cephalon, or posteriorly they may bend outward to the lateral margins of the head; trilobites having this types of sutures are known as proparian. The chief parts of the cranidium, which can be differentiated in nearly trilobites are the glabella and fixed cheeks.

Thorax:

Thorax is divided into three lobes. Each lobe of them are called right plural lobe, axial lobe and left plural lobe respectivelly. The areas on each sides on the thorax are termed as pleural lobes. The ventral surface of each thoracic segment bears a pair of biramous appendages. They are moved by muscles attached to the inside of the exoskeleton.

Pygidium:

It consists of solidly united somites. It may be composed of 1 to 30 or more segments. The shape of pygidium vary in different groups of trilobites. The ventral side of the pygidium carries as many pairs of biramous limbs as there are fused segments.

  

  

  

Taxonomy

It is the systematic biological classification of animals into different groups on the basis of their characteristics.

           The most fundamental unit of biological classification is spices. Next higher unit is genera, genera into order, order in class, class into phylum. Phylum is the largest unit of biological classification.