How Humans Evolved- Chapter 10 From Tree Shrew to Ape
- During the Permian and early Triassic periods, the world’s fauna was dominated
by the therapsids, a diverse group of reptiles that possessed traits, warm bloode
and covered with hair, that linked them to the mammals that evolved later.
- At the end of the Triassic period, dinosaurs filled all the niches.
- One therapsid lineage, evolved and diversified to become the first true mammals.
- With the extinction of the dinosaurs at the beginning of the cenozoic era came
the spectacular radiation of the mammals.
Continental Drift and Climate Change
- The world has become much colder and drier in the last 20 million years, and
particularly variable in the last 800 000 years, these changes likely altered the
course of human evolution.
- Factor that contributed the the changing of the world is continental drift.
- Continents slowly wander around the globe, floating on the denser rock that
forms the floor of the deep ocean.
- 200 mya, there was a huge landmass, Pangaea.
- About 125 mya, Pangaea began to break apart.
- Northern half called Laurasia (North America and Eurasia minus india)
- Southern half, Gondwanaland (the rest of the continents)
- By the time the dinosaurs went extinct 65 mya, Gondwanaland broke up into
- Africa and india separated, india went north into Eurasia, the remainder stayed in
- Separated into south America, antarctia and Australia.
- South America did not join north America til 5 mya.
- Oceans serve as barriers that isolate certain species.
- Continental drift causes climate change, which influences human evolution.
- Size and orientation of the continents have effects on climate.
- Large continents tend to have severe weather.
- When continents restrict the circulation of water from the tropics to the poles,
world climates seem to become coler.
- In the period of peak warmth in the early Miocene, palm trees grew as far north
as what is now Alaska, rich temperate forests reached as north as oslo, and only
the tallest peaks in Antarctica were glaciated. The Methods of Paleontology
- Radiometric methods are used to date fossils.
- Potassium Argon Dating: used to date the age of volcanic rocks, found in
association with fossil material.
- When molten rock emerges from a volcano, argon gas is boiled out of the rock.
- Any argon left in the rock is due to the decay of potassium.
- The ratio of potassium to argon can be used to date volcanic rock.
- If a fossil is discovered in a geological stratum lying under the stratum that
contains the volcanic rock, palaeontologists can be confident that the fossil is
older than the rock.
- Argon-argon dating allows a more accurate dating of single rock crystals.
- Carbon 14 Dating: based on an unstable isotope of carbon that living animals
and plants incorporate into their cells.
- when the organism is alive the ratio of the unstable isotope to the stable isotope
is the same as the ratio of the two isotopes in the atmosphere.
- Once the animal dies, carbon-14 decays into carbon-12, you can measure the
ratio and estimate the amount of time since the organism died.
- Thermoluminescence Dating: based on an effect of high-energy nuclear
particles travelling through rock.
- when they travel through rock they dislodge electrons from atoms, so the
electrons become trapped elsewhere in the rock’s lattice.
- Electron-spin-resonance dating: determines the age of apatite crystals, an
inorganic component of tooth enamel, according the the presence of trapped
- Relative dating methods are magnetic reversals and extinct species.
The Evolution of the Early Primates
- With the breakup of Pangaea during the Cretaceous, angiosperms(flowering
plants) appeared and spread.
- Created new niches.
- Primates were one of the taxonomic groups that evolved to take advantage of
these opportunities. ( fruits, nutrients)
- Ancestors of modern primates were small-bodied nocturnal quadrupeds much
like contemporary shrews.
- Plesiadapiforms give us a clue about what the earliest primates were like.
- They varied from tiny-shrew sized creatures to animals as big as a marmot.
- Teeth were quite variable.
- They were solitary quadrupeds.
- They had claws on their hands and feet, and did not have binocular vision. - Carpolestes simpsoni, had an opposable big toe with a flat nail, but claws on
their other digits.
- The claws on its feet and hands probably helped it climb large-diameter tree
trunks, but it was also able to grasp small supports.
- Had low crowned molars, which are suited for eating fruit.
- Fields of vision did not overlap.
- Plesiadapiforms possess some but not all the traits that characterize modern
- Matt Cartmill : argued that forward-facing eyes provide binocular vision, grasping
hands and feet, and nails on the toes and fingers all evolved to enhance
predation on insects.
- Szalay and Dagosto: hands, feet, nails evolved to facilitate a form of leaping
- Sussman: traits that characterize primates evolved because they enhance the
ability to exploit plant resources.