Download Fossil

Chapter 15 – Theory of
Evolution
15-2: Evidence of Evolution
The Fossil Record

Fossil evidence shows a long history of
Earth – constant change + diversity
 Shows
forms of organisms appeared, lasted for long
periods of time, and then disappeared, only to be
followed by newer forms of life that also eventually
disappeared
Nature of Fossils
 Fossil

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
Trace of a long, dead organism
Found in sedimentary rock layers
Examples:
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Shells
Bones
Teeth
Woody stems (plants)
Whole organisms
Molds
Casts
The Age of Fossils

In, 1669, Steno proposed
the PRINCIPLE OF
SUPERPOSITION

Stated that successive layers of
rock or soil deposited on top of
one another by wind and water

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Layers known as strata
The lowest layer was the
oldest; the top layer was the
youngest
Fossils found in same layer, are
the same age
Geologic Time Scale

Timeline of when
organisms existed

Based on fossil
evidence
The Age of Fossils

Relative age

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States that a fossil is
younger or older
than another fossil
Absolute age

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Its actual age in
years
Can be determined
by radiometric
dating
Distribution of Fossils

Fossil Record inferences:
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Different organisms lived at different times
Today’s organisms are different from those in
the past
Fossils found in adjacent layers are more like
each other than fossils found in deeper or
higher layers

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Lived during same time periods
Can compare when and where different
organisms existed
Transitional species
The fossil records describes a gradual
sequence of forms over time
 Transitional species have intermediate
features between ancestors + older
descendants

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Example:
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Whales
Distribution of Fossils(cont.)

Biogeography

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Study of the locations of organisms around the
world
It compares recently formed fossils with types
of organisms living in the same geographical
area

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Shows that new organisms arise in the areas where
similar forms already lived
Examples:
 Armadillos
 Kangaroos
Distribution of Fossils(cont.)

North + South America

Australia
Anatomy & Embryology

Anatomy

The study of the
body structure of
organisms

Homologous
Structures
 Structures that
originated by
heredity from a
common
ancester
 Ex. - Forelimbs
Anatomy & Embryology

Analogous
Structures
 Features that
have similar
functions but
do not derive
from same
ancestral
structures
 Ex – Wings or
Beaks
Anatomy & Embryology

Vestigial structures

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Structure that seems
to serve no function
but resembles
structures with
functional roles in
related organisms
Examples:
 Tailbone
 Pelvic bone in
whales/snake
 Appendix
 Wisdom teeth
Anatomy & Embryology

Embryology

Study of how organisms develop

Example:
 Vertebrates
Biological Molecules
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Organisms that share many traits should have a
more recent common ancestor than organisms
that share fewer traits
By looking at DNA, RNA, or Amino Acid
sequences, scientists can infer common ancestry
Developing Theory

Mid-1900s
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Integrated theory of natural selection with
genetics
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Called the Modern Synthesis of Evolutionary
Theory
 Widely accepted + applied by scientists
Phylogeny
 Relationships by ancestry among groups of
organisms
 Scientists create a phylogenetic “tree” to show
relationship/ancestry