Transcript fossils

Fossil Record
Recap
 Who can explain to me:
 What is a homologous structure?
 If two organisms share a homologous structure,
what does that say about they relation to each
other?
 What does that say about what their common
ancestor looked like?
 What is a vestigial organ?
 What does a cladogram show?
 What is extinction?
Objectives
 Have a general understanding of the
timeline of life
 Be able to use fossil evidence to
determine ancestry
Fossils
 What is a fossil?
(155 mya, 15 cm
wingspan)
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Fossils
 What is a fossil? A fossil is any trace or
remains of an organism, preserved by natural
processes.
 Fossilized skeletons are the obvious example, but
that’s not all that fossils are limited to.
 Fossils include fossilized droppings, tracks, eggs,
nests, tracks, body imprints, and even whole
bodies preserved in ice, tar, or amber.
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(Baby Psittacosaurus in their nest, killed in
Volcanic eruption 100+ mya)
Fossils
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 Preserved baby wooly mammoth, that’s its REAL
body! Preserved in ice for a little over 10,000 years.
 From such preserved bodies, we’ve sequenced all the
mammoth’s mtDNA and most of its nuclear DNA. Scientists
are also working on extracting viable gametes.
 This, too, is a fossil even though it’s not a rock
skeleton mold.
Fossils
 Coprolites, or fossilized animal dung,
indicate diet, behavior, infections, and
more about the animal.
 It also provides information about the
ecosystem. Even if there’s no independent
imprint of a plant, it can still be recorded in
the droppings of local herbivores, for
instance.
 T-Rex coprolite 50 cm long:
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Fossils
 The oldest insect preserved in amber
comes from 146 million years ago.
Amber has also preserved bacteria,
archaea, plants, and protists.
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Fossils
 There are nearly 100 different ways to
date a fossil.
 Carbon-14 dating, potassium-argon dating,
uranium-lead dating, biostratigraphy…
 Some methods are more chemistry-based,
others are more exclusive to geologists
 Scientists use many of them on each fossil
to be confident of their results.
History of Life
 The “Tree of Life” is vast, beginning 3.8 billion years ago and
with more extinct species than living ones. Humans have only
occupied a small fraction of it. Observe:
 Earth is 4.6 billion years old.
 The first thing that met all the characteristics of life
developed 3.8 billion years ago.
 The first multicellular organism developed 1 billion years
ago.
 The first animal developed 600 million years ago.
 The first species in the genus Homo developed 2.5 million
years ago.
 The first Homo sapiens developed 200,000 years ago.
 http://www.wellcometreeoflife.org/
Using the Fossil
Record
 How can the fossil
record be used with
respect to
evolutionary history?
 The broad trend:
Fossils show that
the form and
structure of
organisms have
changed over time.
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Using the Fossil
Record
 How can the fossil
record be used with
respect to
evolutionary history?
 The broad trend:
Fossils show that
the form and
structure of
organisms have
changed over time.
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decompressor
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Using the Fossil Record
 Fossils also provide
information and the where
and when.
 Dating the fossil tells you the
when.
 The location of the fossil tells
you about the range. (We’ll
do a lab of this soon.)
 Geologists love us
evolutionary biologists, our
fossils have the added
benefit of giving them more
data on tectonic plate shifts.
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Using the Fossil Record
 You find two fossils in the same layer of
rock. One is a plant, the other an insect.
From this, you can conclude:




A.
B.
C.
D.
The insect ate the plant
The insect laid its eggs on the plant.
They lived at the same time.
They lived at different times.
Using the Fossil Record
 You find two fossils in the
same layer of rock. One
is a plant, the other an
insect. From this, you
can conclude:
 C. They lived at the
same time.
 Your conclusions about
their lives will depend on
more than just finding them
in the same layer.
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Using the Fossil Record
 Remember the refrain?
 More _____ = More ______ = More
______ Last Common Ancestor
Using the Fossil Record
 Remember the refrain?
 More SIMILAR = More RELATED = More
RECENT Last Common Ancestor
 Fossils are used to determine ancestry by
comparing them with living organisms and
other fossils.
 Fossils show homologous and vestigial structures
just like living creatures do.
 For example!…
 This fossil is
dated to 145
mya. What are
your
observations?
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 Do you notice
any
homologous
structures that
this species
shares with
birds?
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Using the Fossil Record
 Do you notice
any homologous
structures that
this species
shares with
birds?
 Feathers on
wings, tail, body
 Fused clavicles
 Opposable big
toe
 Many more
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 Do you
notice any
homologous
structures
that this
species
shares with
dinosaurs?
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Using the Fossil Record
 Do you notice any
homologous
structures that this
species shares with
dinosaurs?
 Jaws with pointy
teeth
 Long bony tail
 Three claws on each
arm/wing
 Killing claws on toes
 Many more
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Using the Fossil Record
 This species is called Archaeopteryx. Which
of the following are appropriate conclusions
we can draw?
 A. Archaeopteryx shares a common ancestor with
birds.
 B. Archaeopteryx shares a common ancestor with
dinosaurs.
 C. The common ancestor for Archaeopteryx and
birds had feather-like structures.
 D. The common ancestor for Archaeopteryx and
dinosaurs had a bony tail.
 E. Archaeopteryx is more closely related to birds
than to humans.
Using the
Fossil
Record
 All of the above.
 Archaeopteryx is a
classic “intermediate
form,” a creature with
features definitive to
two groups.
 It’s not a true bird, or a
true dinosaur. It has
recent common
ancestry with both.
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Problems
 Five problems incoming. A sticker if you
get all five correct.
Essential Points About Fossil
Formation
 A fossil is a trace or remains of an organisms that’s
been preserved by natural processes.
 These can include fossilized bones, imprints, tracks,
amber or ice-preserved bodies, etc.
 Any organism can leave a fossil, though this
happens more easily to some organisms than to
others.
 We have fossils of everything from bacteria to plants to
many kinds of animals
 There are more nearly a hundred different ways to
date a fossil. Scientists use many of them on each
fossil to be confident of their results.
Essential Points About Life
History
 The “Tree of Life” is vast, with more extinct
species than living ones. Most of the Earth’s
history has been lifeless, or has only featured
unicellular life. Humans are a very recent
arrival.
Essential Points About Fossil
Data
 Fossils show that the form and structure of organisms
have changed over time.
 They also provide information about where & when.
Fossils found in the same layer of rock come from
organisms that existed in the same time period.
Deeper layers of rock come from further back in
history.
 Fossils are used to determine ancestry by comparing
them with living organisms and other fossils.
 Fossils show homologous and vestigial structures just like
living creatures do.
Extinction!
 What is an extinction?
 If species are all constantly evolving all
the time according to the pressures of
their current environments, why do
extinctions happen?
Videos
 http://videos.howstuffworks.com/hsw/12
698-windows-into-the-past-how-fossilsform-video.htm
 How fossils form

http://www.wellcometreeoflife.org/
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History of life