Fossils and early
primate evolution
Chapter 6
introduction
• Over 99% of everything that has ever lived on Earth
has gone extinct
• Dinosaurs were the dominant species until 65 mya,
when an asteroid hit the earth and wiped almost all of
them out
• This left holes in the ecosystem
• One group that survived were the mammals
introduction
• Review:
• What features do mammals have?
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Hair on body
Live young
Milk to feed young
Constant body temperature
introduction
• Fossils have been known of since ancient Greece, and
Darwin used them in formulating his theory
• William Smith observed strata, or layers of rock that
contained extinct life forms
• Fossils are a way to document evolution of life on
Earth
• Phylogeny: evolutionary relationships
• Chronology: place in time
What are fossils?
• Preserved remains of organisms
• Most are bones, teeth, and shell, or things easily
preserved
• MOST THINGS THAT EVER LIVED WERE
NEVER FOSSILIZED
• This leaves big gaps in the fossil (and evolutionary) record
we try to fill in
• To fossilize, organism must be immediately covered with
sediment, protected from animals, and be in extreme dry
or cold conditions
What are fossils?
• Taphonomy: study of what happens to a fossil from
the time it died until it is discovered
• Fossils are found in different types of rock
• Sedimentary: made from sediments; creates strata
• Volcanic: common for hominins; important for dating
Limitations in
record
• The more samples we have, the better we know the
fossil record
• Some animals well represented, some have only a few
samples
• Fayum Depression (Egypt) is important for primate
fossils
• Would primates living in tropical rainforests preserve
well?
Geologic time
• Have to have new perspective of geologic or
evolutionary time (millions of years, not day-to-day)
• Earth is 4.6 billion years old
• We have recorded major changes of Earth into
• Eras: Paleozoic, Mesozoic, Cenozoic
• Epochs (smaller divisions of eras)
Geologic perspective
• Also have to remember that geography was not always
the same
• Millions of years ago all the continents were connected
into one mass called Pangaea, so this allowed animals
and plants to migrate easily
• Plate tectonics gradually broke this up and made the 7
continents we have today
Early beginnings
• Land animals evolved from aquatic animals
• Lungfish had sacs that they could store air in, as well
as gills
• Also had bones in their fins
• They could move from one pond to another
• Natural selection pushed some of them on land
permanently into land reptiles
• Amphibians are dependent on water (must lay eggs in
it)
• Reptiles have an amniote egg, which does not need
water  land animals
Mammals
• After dinosaur extinction, there were different kinds of
mammals
• Monotremes (mammals that lay eggs)
• Marsupials (have a pouch and embryonic young)
• Placentals (mammals with internal fetal development)
• Monotremes and marsupials are now only in Australia
Mammals
age
• Early thinkers could not fathom the time we measure
now
• Had to adapt to scientific and mathematical
explanations, not biblical ones
• **Law of Superposition: the higher the fossil is in
strata, the younger it is
Dating techniques
• There are two methods of dating fossils
• Relative: compares fossils and tells age as older or
younger in comparison
• Absolute (Chronometric): uses measurements,
chemicals, and math to get a numeric age frame
Relative dating
• Stratigraphic correlation: matches physical and
chemical makeup of different sites of strata
• Ex. If you know the age of volcanic ash, you can date a
fossil older or younger depending on its position to ash
• Chemical dating: uses chemical changes
• Bones absorb flourine from soil; can compare levels to tell
which is older or younger
Relative dating
• Biostratigraphic (Faunal) Dating: if you know when
an animal lived, that can help you date the strata and
other layers of strata around it
• Uses index fossils: animals whose time frame is wellknown
• Example: mammoths are so well-known that they are
good index fossils for dating other nearby remains
Absolute dating
• Relative dating provides an order of what came first,
second, later, latest…etc.
• Absolute dating gives actual ages (numeric)
• Radiocarbon Dating: uses the decaying of carbon
(C14) to get age
• **only used on things that used to be alive
• **only dates back 50,000 years
• Would this be helpful for ancient human ancestors?
Radiocarbon dating
• Carbon is an isotope that changes over time
• All living things are made of carbon
• When a living thing dies, the carbon starts to decay
into nitrogen
• Can measure how much carbon has decayed/how
much is left
• Half-life: the time it takes for half the carbon in the
body to decay. 5,730 years
Absolute dating
• Another method is Radiopotassium or
Potassium/Argon Dating:
• volcanic rock has potassium isotopes
• The potassium decays into argon
• If you date the rock, you know the date of the fossil
inside it because it was formed when the rock formed
• Use the half-life to measure this rate
• Half-life is 1.3 billion
• **only used on rock, and not living things
• **can date much, much older fossils
• Is this helpful for dating ancient human ancestors?
Molecular dating
• DNA is helpful for dating as well
• Idea of Molecular Clock: closely related species have
more similar DNA
• Also trace amount of mutations
• Can use genetic DNA and mtDNA to trace ancestry
and phylogeny
Molecular dating
• For example:
What do you notice about the
placement of humans in the ape
phylogeny?
Ancient climate
• Foaminefera: tiny holes in fossil shells help us
understand levels of oxygen in paleoclimate
• Help us know what eras were hot and humid and
which were cold and dry
• How would this affect primate evolution?
• Human evolution ? (Revisit these questions after we learn
the human ancestors)
• Also think how this would affect sea level and therefore
migration between land masses
Review questions
• What is the difference between relative and absolute
dating? What are examples?
• What types of fossils would be dated with
Radiocarbon and what types with Radiopotassium?
• How can fossils help us recreate evolutionary
relationships, ancient climate, and ancient diet?
Part II
Fossil Primates
• Review of primate features:
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Bone protects eyes
Forward-facing eyes with binocular vision
Grasping hands
Nails instead of claws
Large brain
Long gestation and parental invenstment
Why Primates?
• We know primate features (ch. 5)
• Now focus on why and how these evolved in fossil record
• Arboreal hypothesis: unique primate features are due to life in
trees
• Vision for leaping, hands for grasping branches, intelligence for
understanding 3D space
• But a lot of animals live in trees
• Visual Predation Hypothesis: early primates hunted insects and
unique traits helped with this
• Nails and precision grip to grab bugs, vision to see them
Why Primates?
• But what role do the features of primates play in finding fruit, the
main diet of most primates?
• Vision: can see if fruit is ripe from a distance
• Grasping toes let them hold on to branches while they picked
fruit with hands
• Angiosperm radiation hypothesis (angiosperm means flowering
plant)
• In Cenozoic, primates and fruit evolved together
• All three hypotheses give good explanations
First Primates?
• In Paleocene (between 65-55 million years ago (mya)), the first
primates arose
• They evolved out of mammals.
• …what event happened that led to mammals appearing?
• Plesiadapiforms
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Adaptive radiation of mammals
Many went extinct, probably because of competition with rodents
Lack many of the primate features, but had nails
Very base of the family tree
Proprimates, or the precursor to the primate line
First True Primates?
• Euprimates: true primates, have primate features (eyes protected
by bone, grasping, nails, larger brain)
• Two groups:
• 1. Adapids
• Ancestors of Prosimians/Strepsirrhine
• Resemble lemurs
• 2. Omomyids
• Ancestors of Anthropoids
• Resemble tarsier
Anthropoids Evolve
• In the Oligocene (35-24 mya), there was rapid cooling of the
globe
• This changed habitats
• Most fossils from this time come from the Fayum site in
Egypt
Anthropoids Evolve
• Two main groups:
• 1. Parapithecids
• Primitive, early anthropoids
• 2-1-3-3, so may be ancestor of modern
______________________
• 2. Propliopithecids
• More common group
• 2-1-2-3, so ancestor of _______________________
• Aegyptopithecus is called the “dental ape” because he looked
like a monkey but had a Y-5 molar
Anthropoids Evolve
• Two main groups:
• 1. Parapithecids
• Primitive, early anthropoids
• 2-1-3-3, so may be ancestor of modern Platyrrhines
• 2. Propliopithecids
• More common group
• 2-1-2-3, so ancestor of Catarrhines
• Aegyptopithecus is called the “dental ape” because he looked
like a monkey but had a Y-5 molar
Anthropoids Evolve
• Parapithecid:
Anthropoids Evolve
• Propliopithecid (Aegyptopithecus):
Anthropoids in South
America
• Platyrrhines originated in Africa, but are found only in S
America today
• How did they get there?
• Either they migrated across the ocean or through Antarctica
(which was much warmer then)
• Continents were closer together, oceans may have been
lower, land bridges available
Apes
• Warmer weather accompanied another radiation of primates
• Proconsul (20 mya) is an ape ancestor, the first true Hominoid
• Ape-like dentition
• Adaptations for eating fruit
• However, still small and in trees
• All four limbs equal length
• Not knuckle-walker like apes today
Apes Leave Africa
• Apes began in Africa and then spread to Europe and Asia
• Dryopithecus: Europe, larger body, teeth adapted for fruit,
slow growth and development, larger brains, longer arms
than legs (modern ape locomotion)
Apes Leave Africa
• Sivapithecus:
• found in Asia
• thick enamel for eating tough foods
• ancestor of modern orangutans (skulls almost identical to
modern orangutans)
Apes Leave Africa
• Gigantopithecus:
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Also in Asia
largest primate to ever live
up to 10 feet tall
teeth adapted for tough food
lived up to time of humans
Video
• NOVA “First Primates”
http://www.pbs.org/wgbh/nova/evolution/firstprimates.html
• Use the following page for a study sheet (the next slide is
the same WS you got in class)
• Put any useful information under the picture (geography,
features, especially who they are ancestors of)
• Pg. 183 has a diagram of fossils
Plesiadapiforms
Propliopithecidae
(Aegyptopithecus)
Adapids
Proconsul
Omomyids
Dryopithecus
Sivapithecus
Parapithecidae
Gigantopithecus