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Evolution and Paleontology
The Origin of Species
by Charles Darwin: 1856
Evolution:
• Genetically based changes [due to mutations]
in populations of organisms over successive
generation.
• Changes can result in the formation of new
species.
• Two basic principles of evolution:
1. Variation between individuals
2.Natural selection: a process in which
selected traits are passed on preferentially
from one generation to the next
Basis of Natural Selection:
• The number of adult individuals of a
species is limited by the
environment.
• There is a competition for existence
• Therefore, organisms become
adapted to their environment.
Adaptations: inherited characteristics that help
an organism to survive in a particular
environment.
• Protective coloration-coloration of an animal
which is similar to its environment.
• Protective resemblance-the shape of an
animal’s body is similar to the shape of an
object in its environment.
• Mimicry-similarity in appearance of one
animal to another that has protective value
(Monarch-Viceroy butterflies).
1. Role of geographical separation: necessary
to create new species
Separate species of Galapagos Island finches
were related to an ancestral species from
mainland.
Some Evidence for Evolution
1. Fossils
2. Morphology and Vestigial Characteristics
3. Comparative embryology
4. DNA sequences
Fossils
• Impressions or traces of ancient plants
or animals (the field of paleontology).
Examples of fossils – preserved material
pseudo fossils - rock structures that resemble fossils
but are not
•
•
•
•
Amber-resin specimens
Original remains - a mummy
Gastroliths - gizzard stones swallowed by dinosaurs
Artifacts - stone tools or weapons made by ancient
people
• carbonized forms - carbon remains of organic matter
Examples of fossils – traces
• Mold - all organism is dissolved away, only a cavity
remains. An imprint is an impressions of leaves or
stems in mud or sand
• Cast - the cavity of organism has been filled, and has
formed a replica of the organism
• Mineralized forms - replacements by silica, lime,
calcite, or pyrite
• Coprolites - excrement
Figure 19.4 Revealing Layers, Grand Canyon
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Strata of sedimentary rock with fossils embedded
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Fossils and Related Modern species
• Trilobite: arthropod, related to Horseshoe
crab.
• Belemnite: mollusk with a long internal
skeleton, related to squid.
• Fern fossil: related to modern fern
• Crinoids: echinoderm that looks somewhat
like a flower, related to sea lily
Fossils and Related Modern species
• Calamites - primitive vascular plants, related
to Horsetail and fern.
• Brachiopod - related to mollusk and annelid,
but a separate phylum, has shell with 2
unequal sides
• Diatomaceous Earth – related to diatoms
(have silica shell)
• Shark’s teeth - related to modern shark
Fossilized sea urchin, at least 65 million years old
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Figure 19.16 A Possible Early Flowering Plant, 125 million years old
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Figure 3 Transitional Creature, between fish and tetrapods, 375 million years old
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Figure 16.10 Trilobite, extinct, 370 million years old
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Chapter Opener 19, Crinoids, 360 million years old
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
Brachiopod fossils, 450
million years old. The
largest individuals measure
1.5 cm (0.6") across.
Spiriferina, an extinct brachiopod,
with visible skeleton of the
lophophore
Calamite fossils, 330 million years old
stems
folliage
Belemnites, extinct, 150 million years old
Radioactive “clocks”
• Method based on radioactive decay of isotopes.
• Radioactive isotopes break down (and transform into another
element) at a constant rate called the “ half –life”, which varies from
seconds to billions of years.
Carbon-14 method
• Carbon-12 and carbon-14 are isotopes of carbon. Carbon-14 is
radioactive.
• All living organisms contain a tiny bit of carbon-14. When the
organism dies, its radiocarbon decreases at a constant rate.
• The half-life of C-14 is 5600 years
Comparative Morphology
Homologous structures:
Similar structure, due
to inheritance from a
common ancestor.
But different functions.
Comparative embryology
Molecular
Clocks
DNA sequencing:
gene base sequences
change over time
through the process of
mutation.
*Molecular clock
shows which species
are more closely
related and about how
long it’s since they
have shared a
common ancestor
*