1. Fossil Record (Palaeontological evidences)
The evidences extract from different fields of biological science helps us to project the extent of evolution. Some of the key evidences are very crucial for study the biological evolution. Among the various field of evidences three perspective of evidences which support biological evolution are as follows.
Palaeontological evidences are those evidences which are lived in past and got preserved in the different layer of earth crust, it may be the plant remains or animal remains. Different layer of fossil record define different evolutionary period in the history of evolution.
Fossil are formed in various conditions based on the interaction with environment and by its nature. “The fossils may include original remains of the hard parts (bones,teeth, shell etc) in the sedimentary rocks, petrification of hard and soft parts, carbonised films, moods (impression of organism in rocks), casts (moods filled with foreign material) and as actual remains in peat, amber, asphalt, and ice. The land animals also get fossilised in amber (harden resin), asphalt (harden tar), volcanic ash, peat bogs, and sand deposits or in ice”.[ Source- Organic Evolution;12th edition,V.B.Rastogi ]
There are various categorisation of fossils which are as follows;
i) Unaltered fossils:
In this case due to the favorable condition the entire body of an animal gets preserved in entire body of an animal gets preserved in ice, asphalt, resin, amber, and oilsoaked ground.
e.g Wooly mammoths from Siberia in Artic Tundra gets preserved in ice for thousands of years.
ii) Altered fossils/Petrified fossils:
Petrified fossils are formed by the preservation of organic hard parts of the organism with the minerals. The preservation process is called petrification. Generally petrified fossils are formed in sedimentary rocks on the bottom of lake, rivers or in sea, where the animal’s hard parts gets preserved.
iii) Pseudomorphs and pseudofossils:
“Pseudomorphs are the casts of bodies of an individual that lived in the past. These are formed when the remains get embedded in sedimentary rocks for long times and get dissolved completely by the infiltration of water where the space created get filled with other crystals (mineral compound)”[ Source-Organic Evolution;12th edition, V.B.Rastogi]
Pseudo fossils are false fossils which are formed by the crystals made up of igneous rocks having the pattern resemble with outline of plants,their leaves etc.
iv) Molds and Casts:
Natural Molds are formed by the hardening of material that surrounds the burried organisms. Thier bodies disintegrate and leaving the hollow structure called moods. The surrounding material take the shape and size of the organism and seems as exact cast of the original organism.
v) Micro fossils:
Fossils of spores and pollens (polynofossils) and other vegetal remains are evidences for early environmental condition, by suitable environmental condition these are transformed to fossils fuels by thermal alteration.
e.g. Fossil fuel like coal, gas, and petroleum are formed from remains of phytoplankton, marine and terrestrial algae and lipid rich plants.
vi) Prints or Impressions:
The foot prints of animals or impressions of leaves, stems, skin, and wings etc; left in soft mud are preserved when it changes into a rock.
vii) Tracks and Trails:
The foot prints or tracks and trails of moving animals left in the soft mud get hardens into rocks.
viii) Coprolites:
These are the fossils of faecal matter or droppings. These are formed in association with the animal fossils. The study of coprolites provides information about thier food habits.
2.Transional forms or Connecting links:
The animal exhibiting character of two adjacent taxonomic groups are called connecting links. They afford a very good evidences of organic evolution.
The following are the important connecting links;
e.g.Peripatus:
Peripatus is a living connecting link between annelids and arthropods. It’s arthropods characters are having claws, jaws, haemocoel, trachae and dorsal tubular heart.
The annelidian characters are continuous muscle layers in the body wall, unjointed legs and nephridia. In view of these characters, it is believed that arthropods are originated from annelids.
e.g.Archaeopteryx is another fossil which has the connecting links between reptiles and birds.
3. Geological Time Scale:
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| Source – internet(ciai-fondazione.org) |
Geological time scale depicts the different fossils along with thier time of evolvement. “This scale is like the calender of earth’s past history indicating the evolution of life through chronological stratigraphy of rocks sediments”.[ Source-Organic Evolution;12th edition,V.B.Rastogi]”This period of history of life on earth has been divided into 3 major time frame called as eras which are divided into 12 periods and periods into epochs”.[ Source-Organic Evolution;12th edition,V.B.Rastogi]