Paleontological evidence of evolution

badshah

1. Background
Darwinian evolution permits two general predictions –
(1) if there were an evolution from simple forms to more complex ones, there must be certain structural,
developmental and chemical similarities between different forms of life
(2) there must be a means by which variation in populations arise, and are transmitted from generation to generation.
Paleontological evidence of evolution
Most convincing evidence that evolution has occurred comes from the fossil record of ancient creatures. The study of
ancient life is called palaeontology (Gr., paliaos = ancient + onta = existing things + logos = discourse). The science of
palaeontology links biology with geology and is concerned with the finding, cataloguing and interpreting of fossils.
Paleontology is key to the study of evolution for two reasons.
1. The discovery of fossils showing forms of animals that had never previously been seen began to cast serious doubt
upon creationist theories.
2. Fossils provide the only direct evidence of the history of evolution.

The fossil record provides snapshots of the past that, when assembled, illustrate a panorama of evolutionary change
over the past four billion years. The picture may be smudged in places and may have bits missing, but fossil evidence
clearly shows that life is old and has changed over time.
Early fossil discoveries
In the 17th century, Nicholas Steno shook the world of science, noting the similarity between shark teeth and the rocks
commonly known as "tongue stones." This was our first understanding that fossils were a record of past life.
Two centuries later, Mary Ann Mantell picked up a tooth, which her husband Gideon thought to be of a large iguana,
but it turned out to be the tooth of a dinosaur, Iguanodon. This discovery sent the powerful message that many fossils
represented forms of life that are no longer with us today.
Some theories explaining fossils
The theory of catastrophism Georges Cuvier (1769–1832). The theory of catastrophism holds that a
succession of catastrophes, fires and floods, have periodically destroyed all living things, followed each time by the
origin of new and higher types by the acts of special creation.
Theory Of Uniformitarianism James Hutton, John Playfair and Sir Charles Lyell in the eighteenth and early
nineteenth centuries. The geologic forces at work in the past were the same as those operating now. He arrived at this
conclusion after a careful study of the erosion of valleys by rivers and the formation of sedimentary deposits at the
mouth of rivers. He demonstrated that the processes of erosion, sedimentation, disruption and uplift, carried on over
long periods of time, could account for the formation of fossil-bearing rock strata.
Branches of Palaeontology
Palaeontology is subdivided into the following branches :
 Palaeobotany which deals with the study of plant fossils. It includes palynology which is the study of fossil
spores and pollen grains.
 Palaeozoology which deals with the study of animal fossils and includes invertebrate palaeontology and
vertebrate palaeontology.
 Micropalaeontology which deals with study of small microscopic fossils (microfossils) and their fragments,
e.g., foraminifera, fusulinids and ostracodes.
 Palaeoecology which is the study of ancient organisms and their environment.
Fossils
Fossils (Latin fossilis or fodere = to dig) are the remains or impressions of organisms preserved from the geologic
past. They are virtually anything that is formed by or derived from a prehistoric organism. This includes bones, wood,

2. shells, teeth, skin, pollen, tracks, burrows, and even faeces or dung. The fossil record provides us with evidence that
there were organisms that have become extinct.

How fossils are formed?????
1. Dying In/Near Water Example: trilobite • Water insulates from much decomp/weather • Bacteria eat soft
parts, leave exoskeleton
2. Rapid Sedimentation • Rapid coverage reduces decomp Land/mudslides River delta • Fine grains (clay) allow
detail; coarse grains (sand) don’t
3. Permineralization • Weight of additional layers compacts sediment, makes rock • Mineral-rich water
percolates down • Glues together particles; can replace exoskeleton with rock • Thus, trilobite-shaped rock is
left
4. Uplift • Great, but fossil now buried thousands of feet down! • Tectonic motion can shift around; sea floors
move to land • Of course, many fossils are also destroyed this way
5. Erosion • Still need exposure for discovery • Wind, rain, freeze/thaw, etc. can reveal the fossil • Hope that it
isn’t damaged in process!
Nature of fossils
Fossils are formed in a variety of ways, depending upon the organic material involved and environmental conditions.
They fall into the following two broad classes :
1. Unaltered fossils. Some specimens are preserved relatively unchanged from their original condition; teeth,
bones and shells occasionally are found virtually intact buried in sediments. Even more dramatically, remains of
organisms have been frozen in Arctic ice fields. Mammoths (an extinct form related to elephant) have been found in
their hairy entirety throughout Siberia and have served as an extensive source of fossil ivory. Their flesh was so well
preserved that it was eaten by dogs. Creatures (e.g., largest mammals such as elephants, mastodons and paramylodons)
have been trapped in asphalt or tar-pits at Rancho La Bera in Los Angeles (California). Likewise, in Poland two
skeletons of the woolly rhinoceros, with some of the flesh and skin preserved, have been found buried in oil-soaked
ground. The remains of great Iris deer are found in peat bogs of Ireland.
2. Altered fossils. The organisms become more or less completely changed by the infiltration of minerals from
surrounding rocks, e.g., bones and wood. For such fossils the term petrifaction is applied, i.e., turned to stone. The
petrified forests of Yellowstone National Park and the Arizona Painted Desert of the USA are well known examples of
petrifaction. In Yellowstone, volcanic ash covered the forest about 40 to 60 million years ago. This was followed by
partial mineralisation of the plant tissues by silica and quartz which came from the volcanic debris and was circulated
through the plants by ground water. Millions of years later the forest was exposed when the surrounding volcanic
matter was eroded away. In some regions as many as 27 layers of petrified forests have been discovered.
Significance of Fossils
The study of fossils has great significance. It helps in understanding the prehistoric forms, process of organic
evolution and in reconstructing palaeographic (It deals with study of ancient geography during different geological
eras and epochs) maps. Fossils are extensively used as indicators for prehistoric climate (salinity, sunlight and depth of
water and availability of oxygen, etc.) and as stratigraphic indicators as well. Recently, fossils are used commercially
to detect petroleum reserves, coal reserves, gas reserves and reserves of various metal ores.