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We will be talking about the fossil stories and determining their ages. To know the homologue of a species. A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, etc.
3.
I. THE FOSSIL RECORD
• Provides the best proof of the
history of life showing how
extinct species have lead to
today’s species
“Lucy”, 3.2 MY
Archaeopteryx, 150 MY
4.
Becoming a Fossil (Part 1)
(excerpts from Bill Bryson’s book)
In order to become a fossil, several things must happen. First, you must die
in the right place. Only about 15% of rocks can preserve fossils, most
being sedimentary rocks. So the deceased usually needs to become buried
in sediment, the best chance is being buried underwater and decomposing
without exposure to oxygen, allowing the bones and hard parts, and
sometimes soft tissue, to be replaced by dissolved minerals, creating a
petrified stone version of itself. Then as the sediments in which the fossil
lies are pressed, folded and pushed about by Earth’s processes, the fossil
must somehow maintain an identifiable shape. Finally, after tens of
millions to hundreds of millions of years of being hidden away, it must be
found and recognized as something worth keeping.
• Why do you think the fossil record (almost 95% of it ) is mostly marine life?
Formation of Fossils (Summary)
• Organism is buried in sediment under water (sometimes: ice, amber or tar)
• Hard parts (bone& shell) are slowly replaced by minerals dissolved in water
5.
The Story Fossils Tell
• What type of rock is it?
• Provide an observation & an inference about this fossilized animal.
• If this fossil was found in central Cumberland County, PA, how old is
it? (Use the Geologic Map on next slide)
6.
• What type of rocks are most common in Bucks County?
• What age fossils might you find in Bucks County?
7.
Transitional Species (Common Ancestors)
• Location where two species evolutionary
path connect on the “tree of life”
• Scientists search for common ancestors
in the fossil record to show the
evolutionary connection between species
& how they change over time.
10.
Transitional Species Example – Whale Evolution
* Read more on Whale Evolution in the textbook (pgs 112-113)
* Whale Evolution video clips
11.
Becoming a Fossil (Part 2)
(excerpt from Bill Bryson’s book)
It isn’t easy to become part of the fossil record. The fate of
nearly all living things (over 99.9% of them) is to decompose to
nothing. Even if you make it into the small pool of organisms, that
don’t breakdown to nothing, the chances of being fossilized are very
small. Only about one bone in a billion, it is thought, ever becomes
fossilized. If that is so, it means that the complete fossil legacy of all
the Americans alive today (that’s about 300 million people with 206
bones each) will only be about 50 bones, one quarter of a complete
skeleton. That’s not to say that any of these bones will actually be
found. Fossils are in every sense extremely rare. Most of what has
lived on Earth has left behind no record at all. It has been estimated
that less than 1 species in 10,000 has made it into the fossil record.
What we have in the fossil record is the smallest of samplings of all
the life that has existed on Earth.
12.
Completeness of the Fossil Record?
13.
How do we know how old a fossil is?
TWO Ways to Date Fossils
• Relative age dating
– approximation of dating by
comparing rock layers
• Absolute age dating
– Precision of dating by
measuring radioactive
decay of elements in rock
14.
Relative Age Dating
• Relative age dating follows the Law of Superposition (older rocks
are found under younger rocks)
• Exception to the rule – unconformities (break in the rock record)
• Index Fossil – an organism that lived during a specific period of
time and is abundant.
15.
Absolute Age Dating
• Radioactive Elements: unstable atoms giving off radiation (protons & neutrons) to
become stable.
– Ex: Uranium-238 & Carbon-14
• Radioactive dating: Radioactive decay (going from unstable to stable) occurs at a
constant rate called a half life. Each radioactive element has its own half life.
• Half life: the amount of time it takes for half the radioactive atoms in a substance to
become stable.
• Examples:
– Uranium-238 has a half-life of 4.5 billion yrs (becomes Lead)
– Carbon-14 has a half-life of 5730 yrs (becomes Nitrogen)
Example of Absolute Age Dating
Red Dots are radioactive elements
Green Dots are stable elements
– *****PUT ANOTHER EXAMPLE ON THE BOARD
16.
II. Comparative Anatomy
• Homologous Structures
• Vestigial Structures
17.
Homologous Structures
• body parts from different organisms that
have the same structures, but different
functions, supporting the idea of a shared
common ancestor
• EX: vertebrate forelimb bones
20.
Homologous Structures Analogous Structures
Similar in anatomy Dissimilar in anatomy
Doing dissimilar functions Doing similar functions
Develop in related animals Develop in unrelated
animals
Inherited from a common Not inherited from recent
ancestor common ancestor
Similar developmental Developmental pattern is not
pattern similar
Similar structure and Origin Dissimilar in structure and
origin
21.
Homologous OR Not?
Cephlopod
Cnidarian
Arthopod
24.
Homologous OR Not
As already discussed Homologous Structures between
species provide evidence that the species shared a
common ancestor, as shown in the mammal forelimb
examples, displaying the same structure but adapting
different functions for their forelimbs.
Some times in nature, unrelated species will evolve
similar functions through different evolutionary paths
using unrelated structures. These types of structures are
called Analogous Structures and they do not show
evidence of evolution from a common ancestor.
25.
Which limb is NOT homologous in each set? Why?
Human
Octopus Lizard
Human
B
Lizard
Bird
Whale
Grasshopper
26.
Common Ancestors
Homologous structures are
inherited from common
ancestors. The octopus limb
could only be homologous to
the lizard limb if they both
inherited the limb from a
common ancestor. This
family tree shows how the
octopus is related to
vertebrate limbs. Vertebrate
limbs and octopus limbs
evolved independently after
their point of common
ancestry, so they were not
inherited from a common
ancestor. Therefore, they
are not homologous, they are
considered analogous. The
same is true of the
grasshopper leg.
27.
Homologous OR Not
GAME
Helpful Hint: For each set of pictures, ask yourself
if the structure or adaptation evolved between the
species from a shared common ancestor OR did the
structure evolve independently between the two
species showing no common ancestor linking the
structure or adaptation together.
DIRECTIONS: Keep Score of how many you and
your group get correct.
28.
1. Are the wings of a bat (mammal) and the
wings of a robin (bird) homologous?
29.
2. Fins of a shark (fish) and the fins of a dolphin
30.
3. The limbs of an eagle and the limbs of a penguin?
31.
4. Wings of a dragon fly and the wings of a butterfly?
32.
5. Are all of these different leaves Homologous?
33.
6. No limbs on a water snake (reptile) and no limbs on
an eel (fish)?
34.
7. Opposable thumbs of the primitive primate, bush
baby, and our opposable thumbs?
35.
8. The front teeth on a beaver and the tusks on an elephant?
36.
9. The scales on a brown trout (fish) and the
scales on a lizard (reptile)?
37.
10. Gliding adaptation of the marsupial sugar glider from
Australia and the placental gliding squirrel of the Americas?
38.
Answers
1. No (they do not share a common ancestor with wings)
2. No (they do not share a common ancestor with fins)
3. Yes (both are birds that have adapted different uses for their wings)
4. Yes (both are insects that evolved from insects with wings)
5. Yes (all are types of modified leaves from different plants)
6. No (they do not share a common ancestor without limbs)
7. Yes (both are in the primate family which all have opposable thumbs)
8. Yes (both are mammals with modified front teeth)
9. No (they are not closely related, fish and reptile, scales evolved
independently)
10. No (they are different groups of mammals, placental and marsupial, that do
not share gliding ancestors)
39.
Vestigial Structures
• structures that are found in an organism but appear
to serve no function (reduced in size)
• they are remnants of an organism’s evolutionary past
– Ex: Whales and snakes have pelvic bones; manatees “sea
cows” have finger nails on their fins
– Humans?
• ear muscles
• canine teeth
• Goose bumps
• appendix
• Tail bone
• Wisdom teeth
41.
The same muscles
(arectores pilorum) that
enable a cat to do this:
also enable us to do this:
42.
III. Comparative Embryology
• similarities in the developmental pattern of
organisms exist because of a common ancestor
– vestigial gill slits/pouches
– bony tail
– covered in a fine hair
– Two chambered hearts
Human embryo Pig embryo Chicken embryo
43.
Comparative Embryology in Vertebrates
•All vertebrates are
similar in early
stages of
development.
•Differences
accumulate as
development
continues.
•New development
instructions are
added to old
instructions inherited
from ancestors.
44.
Comparative Embryology in Vertebrates
•All vertebrates are
similar in early
stages of
development.
•Differences
accumulate as
development
continues.
•New development
instructions are
added to old
instructions inherited
from ancestors.
46.
IV. Comparing Genetics
• An organism’s evolutionary history is held in their DNA
sequence (genetic code)
• If a species changes, their DNA changes
• Genetic testing compares the similarity of DNA between
organisms
• The more closely related the species are to each other
the more similarities they share in their DNA
• Ex. Chimpanzees & Humans have over 98% the same DNA
48.
Cytochrome c
Cytochrome c is a protein organisms need for
respiration. Proteins are made of an amino acid
sequence that is determined from our DNA
sequence. So if the amino acids in the cytochrome
c protein is slightly different between species it
also means their DNA is slightly different.
Virtually every organism uses cytochrome c;
however, each species’ cytochrome c differs
slightly from other species. The differences
among cytochhrome c exist in the amino acid
sequence which were produced by mutations in
the species DNA. These mutations occurred after
the ancestors of the living species diverged.
Therefore, if two species shared common
ancestors until fairly recently, their DNA and
proteins are likely to be more similar.
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