Paleontology is the study of past life based on fossil and fossilization record. The fossils are the petrified remains or impressions or imprints of the hard parts of the ancient organisms. They are preserved in the sedimentary rocks (gradual deposition of soil particles in layer after layer) or other media like volcanic ash, ice, sand, mud, etc. to study about evidences from Paleontology. Examples: Archaeopteryx left bones and feathers in the form of impression.
Note:
Dinosaurs left foot print on the hard rocks called Imprints.
Leonardo da Vinci (1452-1519) is called father of Paleontology.
Georges Cuvier (1800) is called father of modern Paleontology.
Paleozoology is the branch of Paleontology which deals about the study of animal fossils.
Four general types of Fossils
They are Unaltered, Petrified, Moulds and Casts and Prints
Unaltered
Whole bodies of extinct organisms have been found frozen in ice at the poles (fossilized resin of confers). Example: Elephant like Wooly mammoths were found buried in ice inSiberia.
Petrified
According to evidences from Paleontology the fossil includes the hard parts of extinct organisms such as bones, shell, teeth, etc. Sometimes these hard parts are found unchanged but mostly they are found with their organic parts or completely replaced by deposition by minerals. Replacement of organic parts by minerals deposition is called petrification.
Moulds and Casts
Evidences from Paleontology suggests that moulds of hardened and fossilized mud that surrounds an extinct organisms have retained true copies of their shapes. During moulding buried organisms are completely replaced by minerals.
Prints
It includes print of print of foot, wings, bone, skin, etc. in soft mud.
Evidences from Comparative Cytology
According to evidences from comparative cytology all forms of life come from cellular level. The cell is structural and functional unit of life. This indicates basic relationship among living forms. All cells contain cell membrane made up of double layered lipo proteins. They have DNA - RNA protein information and communication system. All the cells utilize the glycolytic pathway and have a Krebs cycle and an electron transport system as pointed by the evidences from comparative cytology.
Embryology is the study of development of an egg into the adult. Evidences from Embryology based on comparative developmental studies of embryos of various organisms. Some examples are: All multicellular start their life as a Zygote. Zygote is a single celled and comparable to Protozoa. Zygote undergoes a series of events like morula, blastula and gastrula. Cell of blastula organize to differentiate into two germ layers i.e. Ectoderm and Endoderm (in diploblastic animals). Blastula changes into gastrula. During gastrula stage (in triploblastic) the third germ layers mesoderm originates. According to Evidences from Embryology the developmental stages upto gastrula stage in all metazoans are similar i.e. Monophyltic origin. The development of heart in embryos of fish is two chambered and same condition of the heart retained in adult stage. The development of heart starts as two chambered in amphibia, reptiles, birds and mammals but become three chambered in adult amphibia, three and half in reptile (in crocodile 4 chambered), in aves and mammals four chambered. The presence of gills slits is one of salient characters of chordates; which remains as such in primitive characters (protochordata). The gill pouch and gill slits develops into gills in fish for aquatic respiration. But in adult amphibia, reptiles, aves and mammals replaced by lungs for Aerial respiration.
Von Baer (1828) Von Baer suggests basic principles of Evidences from Embryology development, which are as follows: During development general characters appear before special characters. From more general, the less general and finally the special characters appear. During development, an animal develops progressively from the form of other animals. Young stages are like young stage of ancestors or embryonic stages of lower animal, but not like adults of those animals.
Biogenetic Law Biogenetic Law was proposed by Ernest Haeckel (1866), also called Recapitulation Theory. He studied a lot about Evidences from Embryology. It states that ontogeny repeats phylogeny. It means all organisms during their development receives ancestral characters (ontogeny). This historical evolution is called phylogeny.Ontogeny: It means development of organs, Phylogeny: It means ancestral characters. Example: Gills, gill slits, tail, tail fin, lateral line, sense organs, etc. in the tadpole larva of frog.
Direct and indirect proofs of existence of evolution are:
Evidences of Organic Evolution from Comparative Anatomy Study of functional anatomy is called Tectology.
Evidences of Organic Evolution from Homology and Homologous Organs The structures which are different in appearance and perform different functions but have similar basic structure and origin are called homologous organs. The relationship between the structures having common basic plan and similar development origin is called homology or divergent evolution. Some important examples are: Fore limbs in vertebrates like flippers (paddles) of whale or seal, wings of bat, cat's paw, front foot of horse, human hand and wings of birds. They are built on same pentadactyle plan (5- digits) but performs different functions. They show similar arrangement of structure like bones, blood vessels, muscles, nerves, etc. Function: In seal – swimming, bird and bat – flying, in cat – running and walking, in horse – running, in man – grasping.
Evidences of Organic Evolution from Analogy and Analogous Organs The organs which are different in the basic structures and developmental origin but appear similar and perform similar function. The relationship between structures of different groups of animals due to their similar function is called analogy or convergent evolution. Example: Wings of insects and birds. They are different in basic structure and origin. Insects wing are formed from integument while the bird wing is modified fore limb. They are analogous organ, as both are flat and are adapted for flight. Fins of fishes and the flippers of whale are of similar function but structurally different. The sting of honey bees and scorpions perform similar function and look alike. They are analogous structures because the sting of honey bee is a modification of its ovipositor while that of scorpion is modified by last abdominal segment.
Evidences of Organic Evolution from Vestigial Organs Those organs of the body which were functional in ancestors but non-functional in the descendants. Example: There are about 90-100 vestigial organs in man. Important vestigial organs in man are – Coccyx (tail bone), nictitating membrane (third eyelid), muscles of ear pinna, caecum, vermiform appendix, canine, body hair, mammary gland in male, segmental muscles on abdomen, etc. Hind limbs in Python, Pelvic girdle and pinna of whale, wings of flightless birds, etc are example of vestigial organs. Snake do not possess legs because legs are degenerated during evolution.
Evidences of Organic Evolution from Connecting Link The living organisms having intermediate characters between two group are called connection link. Example: Virus, Euglena, Proterospongia, Peripatus, Neoplina, Balanoglossus, Dipnoi, Archaeopteryx, Prototheria. Protopterus (Lung Fish): It is a connecting link between bony fish and Amphibia. In fish paired fins, dermal scales, lateral line system and gills. In amphibians internal nares, lungs and 3 chambered heart. Ornithorhynchus (Duck billed Platypus) and Tachyglossus (spiny and eater) are egg laying mammals. They act as connecting links between mammals. Mammalian characters are hair, diaphragm, mammary glands etc. while reptilian characters are large coracoid, being oviparous, laying eggs and having cloaca.
Evidences of Organic Evolution from Living Fossils Those animals which underwent little change during long geological periods. Some important living fossils are:
Limulus and Peripatus – Arthopoda Nautilus and Neopilina – Mollusca Lingula – Brachiopoda Latimeria – Coelacanth fish Sphenodon – Reptilia Didelphis – Opossum
Evidences of Organic Evolution from Missing Links Those extinct organisms which had the characters of two different groups of animals and confirm the path of evolution as lie in between these groups. Arcaeopteryx, also called lizard bird. It is a missing link between reptiles and birds. Evidences of Organic Evolution from Reptilian Characters: Presence of similar teeth in Jaws.
Each finger ending into a claw.
A long tail with free caudal vertebrae.
Presence of keelless sternum.
Evidences of Organic Evolution from Avian Characters: Presence of feathers of the body. Rounded cranium. Forelimbs modified into wings, have three fingers. Presence of furcula or wish bone. Above mention characters show that the birds have evolved from reptilian ancestors. So birds are glorified reptiles (Huxley).
Evidences of Organic Evolution from Atavism or Reversion The sudden appearance of some ancestral features in some individuals is called atavism. It means non functional organs of the ancestors become functional in descendants. Examples: Large canine in man, thick hair on body, functional nipples in male, elongation of tail bone, etc.
m cellular level. The cell is structural and functional unit of life. This indicates basic relationship among living forms. All cells contain cell membrane made up of double layered lipo proteins. They have DNA - RNA protein information and communication system. All the cells utilize the glycolytic pathway and have a Krebs cycle and an electron transport system as pointed by the evidences from comparative cytology.
