Fossil Evidence of Evolution

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Fossil Evidence of Evolution
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Contemporary Scientific History of the Universe
13.7 billion years in 30 volumes -each volume
450 pages -each page 1 million years
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What is a fossil?

• physical evidence of an organism that lived long
  ago.
• Examples skeletons, shells, leaves, seeds,
  imprints, tracks, and even fossilized feces and
  vomit.
• The vast majority of fossils are the remains of
  the hard parts of extinct organisms.

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How do fossils form?

• Fossils form when body parts or impressions are
  buried in rock before they decompose.
• The evidence is preserved in the rock through
  geochemical processes. Fossils are not usually
  the actual bodily remains.
• Fossilization is an extremely rare event.
• Most ancient species are not represented in the
  fossil record.

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What is the fossil record?

• the collection of fossils that represents the
  preserved history of living things on earth.
• The fossil record provides the dimension of time
  to the study of life.
• It shows that Earths organisms have changed
  significantly over extremely long periods of time.

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(each layer period of time)
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The fossil record is not perfect...but

• It abundantly documents continuous change.
• It is sequential in nature.
• It contains numerous examples of evolutionary
  transitions.
• It is continually growing as new fossils are
  discovered.

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General Patterns in the Fossil Record

• Deeper rock layers were laid down before the
  layers above them. Thus, fossils in lower layers
  are older than those in upper ones.
• Fossils occur in a definite sequential order,
  from species that appear primitive to modern
  appearing ones.
• The species representing different lines of
  descent become more similar to each other as they
  approach their common ancestors.

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• Comparison of the earliest members of four
  families of odd-toed ungulates.
• (a) Hyracotherium (Horses)
• (b) Hyrachyus (Rhinos)
• (c) Heptodon (Tapirs)
• (d) Eotitanops (Brontotheres)

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• Fossils document the evolution of the modern
  camel from ancestral forms existing in much
  earlier geologic ages.
• Because we can consistently trace lineages like
  this backwards in time, evolutionary descriptions
  of earths history fit the facts of the geologic
  record.

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Fossils Form in Sedimentary Rock
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• The Geologic
• Time Scale
• Earths history is organized into four distinct
  ages
• Precambrian
• Paleozoic
• Mesozoic
• Cenozoic
• The boundaries between these major periods of
  geologic time are defined by major changes in the
  types of fossils found in the rocks deposited
  during these eras.

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Geologic Time Scale See page 337
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Geologic Time Scale
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Dating the Fossil Record

• The discovery of radioactivity enabled scientists
  to accurately determine the ages of fossils,
  rocks, and events in Earths past.
• Determining the age of a rock involves using
  minerals that contain naturally-occurring
  radioactive elements and measuring the amount of
  decay in those elements to calculate
  approximately how long ago the rock formed.

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Age Determination Using Radioactive Isotopes

• Radioactive isotopes are useful in dating
  geological materials because they convert or
  decay at a constant, and therefore measurable,
  rate.
• Age determinations using multiple radioactive
  isotopes are subject to very small errors of
  measurement, now usually less than 1.

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Step 1 List ALL of the long-lived radioactive
nuclides.
150Gd 2.1 x 106 no 152Gd 1.1 x
1015 yes 153Dy 1.0 x 106 no 174Hf 2.0 x
1015 yes 176Lu 3.5 x 1010 yes 182Hf 9 x
106 no 187Re 4.3 x 1010 yes 190Pt 6.9 x
1011 yes 192Pt 1.0 x 1015 yes 205Pb 3.0 x
107 no 232Th 1.40 x 1010 yes 235U 7.04 x
108 yes 236U 2.39 x 107 yes - P 237Np 2.14 x
106 yes - P 238U 4.47 x 109 yes 244Pu 8.2 x
107 yes 247Cm 1.6 x 107 no
10Be 1.6 x 106 yes - P 40K 1.25 x
109 yes 50V 6.0 x 1015 yes 53Mn 3.7 x 106 yes
- P 87Rb 4.88 x 1011 yes 93Zr 1.5 x
106 no 97Tc 2.6 x 106 no 98Tc 1.5 x
106 no 107Pd 7 x 106 no 115In 6.0 x
1014 yes 123Te 1.2 x 1013 yes 129I 1.7 x
107 yes - P 135Cs 3.0 x 106 no 138La 1.12 x
1011 yes 144Nd 2.4 x 1015 yes 146Sm 7.0 x
107 no 147Sm 1.06 x 1011 yes
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Step 2 Order Nuclides by half-life
Listing of nuclides by Half-Life 50V 6.0 x
1015 yes 144Nd 2.4 x 1015 yes 174Hf 2.0 x
1015 yes 192Pt 1.0 x 1015 yes 115In 6.0 x
1014 yes 152Gd 1.1 x 1015 yes 123Te 1.2 x
1013 yes 190Pt 6.9 x 1011 yes 138La 1.12 x
1011 yes 147Sm 1.06 x 1011 yes 87Rb 4.88 x
1011 yes 187Re 4.3 x 1010 yes 176Lu 3.5 x
1010 yes 232Th 1.40 x 1010 yes 238U 4.47 x
109 yes 40K 1.25 x 109 yes
235U 7.04 x 108 yes 244Pu 8.2 x
107 yes 146Sm 7.0 x 107 no 205Pb 3.0 x
107 no 236U 2.39 x 107 yes - P 129I 1.7 x
107 yes - P 247Cm 1.6 x 107 no 182Hf 9 x
106 no 107Pd 7 x 106 no 53Mn 3.7 x 106 yes -
P 135Cs 3.0 x 106 no 97Tc 2.6 x
106 no 237Np 2.14 x 106 yes - P 150Gd 2.1 x
106 no 10Be 1.6 x 106 yes - P 93Zr 1.5 x
106 no 98Tc 1.5 x 106 no 153Dy 1.0 x 106 no
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Step 3 Eliminate nuclides continually produced
by ongoing decay processes
Nuclide Half-Life In
Nature? (years) 50V 6.0 x 1015 yes 144Nd 2.4
x 1015 yes 174Hf 2.0 x 1015 yes 192Pt 1.0 x
1015 yes 115In 6.0 x 1014 yes 152Gd 1.1 x
1015 yes 123Te 1.2 x 1013 yes 190Pt 6.9 x
1011 yes 138La 1.12 x 1011 yes 147Sm 1.06 x
1011 yes 87Rb 4.88 x 1011 yes 187Re 4.3 x
1010 yes 176Lu 3.5 x 1010 yes 232Th 1.40 x
1010 yes
Nuclide Half-Life In
Nature? (years) 238U 4.47 x
109 yes 40K 1.25 x 109 yes 235U 7.04 x
108 yes 244Pu 8.2 x 107 yes 146Sm 7.0 x
107 no 205Pb 3.0 x 107 no 247Cm 1.6 x
107 no 182Hf 9 x 106 no 107Pd 7 x
106 no 135Cs 3.0 x 106 no 97Tc 2.6 x
106 no 150Gd 2.1 x 106 no 93Zr 1.5 x
106 no 98Tc 1.5 x 106 no 153Dy 1.0 x 106 no
FACT Every nuclide with a half-life of less
than 80 million years is missing from our region
of the solar system, and every nuclide with a
half-life of greater than 80 million years is
present. Every single one!
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Intermediate Forms

• So many transitional fossils have been found
  that it is often hard to tell when the transition
  actually occurred.
• Actually, nearly all fossils can be regarded as
  intermediates because they are connections
  between their ancestors and their descendants.

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Example The Transition to Land
365 million years ago
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Video
385 million years ago
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Direct Ancestor or Close Relative?

• Ancestor-descendant relationships can only be
  inferred, not directly observed.
• No matter how long we watch, no two fossils will
  ever reproducewe must look for other ways to
  determine relatedness.
• Because genetically similar organisms typically
  produce similar physical features, we can use
  fossils to help us recognize related species in
  the history of life.

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Archaeopteryx An Intermediate Form Between
Reptiles and Birds
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Archaeopteryx An Intermediate Form

• While considered the earliest bird, it retained
  many distinctly reptilian features.
• A mosaic of 24 distinct anatomical features
• 3 bird-like
• 17 reptile-like
• 4 intermediate
• Are dinosaurs still alive?

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Feathered Dinosaurs from the Liaoning Fossil Beds
in China
Caudipteryx zoui
Microraptor gui
Sinornithosaurus millenii
Mei long
Sinosauropteryx prima
Video The Liaoning Forest
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Reptile to Mammal Transition

• In mammals, each half of the lower jaw is a
  single bone called the dentary whereas in
  reptiles, each half of the lower jaw is made up
  of three bones.
• Evolution of this jaw articulation can be traced
  from primitive synapsids (pelycosaurs), to
  advanced synapsids (therapsids), to cynodonts, to
  mammals.

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• Two of the extra lower jaw bones of synapsid
  reptiles (the quadrate and articular bones)
  became two of the middle-ear bones, the incus
  (anvil) and malleus (hammer).
• Thus, mammals acquired a hearing function as part
  of the small chain of bones that transmit air
  vibrations from the ear drum to the inner ear.

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Evolution of Turtles

• Turtles have a shell and no teeth, both unique
  traits among reptiles.
• Scientists predicted that the oldest turtles
  should show evidence of these changes.
• November 2008 The oldest known turtle,
  Odontochelys, has an incomplete shell and teeth.

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Evolution of Snakes

• Snakes are tetrapods with no legs.
• Evolution predicted primitive fossil snakes with
  evidence of limbs.

• Evolution also predicted intermediate forms
  between lizards and snakes.
• Adriosaurus, a fossil lizard with hindlimbs,
  reduced forelimbs, and an elongated body.

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Evolution of Bats

• Until recently, the oldest known bats in the
  fossil record, like modern bats, could fly and
  echolocate.
• Scientists long wondered which ability came
  first, and they predicted the existence of fossil
  species that had one, but not both, of these
  abilities.

Palaeochiropteryx tupaiodon 47 mya
Icaronycteris index 50 mya
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Prediction Confirmed!

• Flying evolved first, echolocation came after.
• Onychonycteris finneyi is the most primitive
  known species of bat
• Lacks evidence of echolocation.
• Short, broad wings with claws on all five fingers
  (modern bats have no more than two claws).
• Longer hind legs and broader tail than modern
  bats.
• Shorter forearms than modern bats suggest less
  efficient flying.

Onychonycteris finneyi 52.5 mya
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Evolution of Whales

• The evolution of whales and dolphins is one of
  the best-documented transitions in the fossil
  record.
• Fossil, morphological, biochemical, vestigial,
  embryological, biogeographical, and
  paleoenvironmental evidence all support the
  inference that whales evolved from four-legged
  land-dwelling mammals.

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• The descent of whales from land-dwelling mammals
  is well documented by transitional fossils.
• The tentative reconstruction shown here is based
  on extensive fossil evidence.
• Many of these transitional fossils have features
  that were exactly what paleontologists had
  predicted they would find in ancient whales.
• For instance, the fossils show transitions in
  dentition (teeth), the ear canal, the loss of
  hind limbs, the development of the tail fluke,
  and the transition of the nostrils to the
  blowhole.

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The fossil record shows that whales and dolphins
probably evolved from a group of hoofed mammals
called Artiodactyls. Evidence suggests that these
were the same ancestors of a well-known group of
hoofed mammals called Mesonychids. Mesonychids
had notched, triangular teeth similar to those of
early predatory whales. Paleontologists
previously considered Mesonychids ancestral to
whales, but they now consider them to be a
sister group instead.
Mesonyx, a primitive mesonychid
60 million years ago
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Artists visualization of Sinonyx, another
primitive Mesonychid
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Later fossils in the series show the Pakicetids,
a group of carnivorous land mammals with
peculiarities in the bones of the ear that have
only been found in whales. Pakicetid teeth look a
lot like those of fossil whales, but are unlike
those of modern whales. The shape of their teeth
suggests that they were adapted for hunting fish.
Pakicetus
50 million years ago
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Artists visualization of Pakicetus, a Pakicetid
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Later, a species existed that had front forelimbs
and powerful hind legs with large feet that were
adapted for paddling. This animal, known as
Ambulocetus, may have moved between water and
land. Its fossilized vertebrae show that this
animal could move its back in a strong up and
down motion, which is the method modern whales
and dolphins use to swim and dive. It also had a
nose adaptation that enabled it to swallow
underwater, the ability to hear underwater, and
teeth similar to primitive whales.
Ambulocetus
47-48 million years ago
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Artists visualization of Ambulocetus natans
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A later fossil in the series, Rodhocetus, shows
an animal with smaller functional hind limbs and
even greater back flexibility. The ankle bones
are similar to existing hoofed land mammals such
as the hippopotamus. The forefeet of Rodhocetus
had hooves on the central digits, but the hind
feet had slender toes which may have supported
webbing. This suggests that Rodhocetus was
predominantly aquatic.
Rodhocetus
46-47.5 million years ago
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Artists visualization of Rodhocetus
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Maiacetus
At about the same time, a species known as
Maiacetus also existed. This species had big
teeth that were well-suited for catching and
eating fish, suggesting that they made their
living in the sea. However, other evidence
suggests that they may have came onto land to
rest, mate, and give birth.
47.5 million years ago
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Artists visualization of Maiacetus
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Artists visualization of Protocetus
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Basilosaurus fossils represent a recognizable
whale, with front flippers for steering and a
completely flexible backbone. This animal had
small hind limbs, although they are thought to
have been nonfunctional.
hind limbs
Basilosaurus
35 - 45 million years ago
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Artists visualization of Basilosaurus
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Dorudon was a primitive whale that also had small
hind limbs. When they were first found in the
same deposits as Basilosaurus, the two animals
were so similar that Dorudon were thought to be
baby Basilosauri. They are, in fact, different
species, and now baby Dorudon are also well known.
Dorudon
37 million years ago
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Artists visualization of Dorudon
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Evolution of Modern Whales

• Toothed whales have full sets of teeth throughout
  their lives.
• Baleen whales only possess teeth during an early
  fetal stage and lose them before birth.
• Fossil evidence indicates that the ancient whale
  Janjucetus, with skull features that make it the
  earliest known baleen whale, also had a full set
  of teeth.

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Artists visualization of Janjucetus
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Both Teeth and Baleen?

• The skull of an ancient toothed whale called
  Aetiocetus has holes for blood vessels that were
  likely used to nourish baleen.

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Artists visualization of Aetiocetus
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Evolution of the Blowhole
Nostrils at front of skull
Nostrils at top of skull
Pakicetus 50 million years ago
Beluga Whale Today
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Evolution of Echolocation

• Fossils demonstrate that whales acquired
  underwater hearing in stages.
• Pakicetus lacked the fat pad extending to the
  middle ear which modern whales have.
• Basilosaurus, transmitted sound to the middle ear
  as vibration from the lower jaw.
• Todays toothed whales can echolocate, the melon
  directs sound outward and the lower jaw works as
  a receptor.

Melon
Pakicetus 50 million years ago
Basilosaurus 35-45 million years ago
Tursiops Bottle-nosed Dolphin
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Giving Birth

• Modern whales are born tail first to prevent
  drowning in the birth canal.
• Fossil evidence shows a Maiacetus baby with its
  head facing the birth canal, suggesting that this
  species still gave birth on land.

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Other Transitional Fossil Series

• Primitive fish to sharks and rays.
• Primitive fish to bony fish.
• Amphibians to reptiles.
• Land mammals to manatees.
• Five-toed ancestors to horses.
• Bipedal apes to humans.

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Conclusion

• Many critical gaps in our knowledge remain.
• These gaps may or may not be filled by new
  evidence in the future.
• However, it is certain that important discoveries
  will continue to be made that will likely
  intrigue us, possibly surprise us, and definitely
  enrich our understanding of the evolutionary
  history of life.