Lec 8: Diversification - Moving onto land Flashcards
What is life like during the Proterozoic?
- no life on land
- photosynthesis evolves
- eukaryotes evolve
- bacterial mats grow fast
What happens at the beginning of he Proterozoic?
the great oxygenation event
What was life like during the Cambrian?
- shells and hard bodies dominate
- animals become more motile
- explosion of new body types in animals
- first chordate (pikaia), ancestor of all vertebrates
What was life like during the Ordovician?
- first vertebrates evolve from Pikaia
- complex animals and plants have evolved, but have not left the water
Why is desiccation a barrier to adapting to land?
- organisms dry out easily (especially smaller ones)
- they cannot be waterproof, because they need to allow for the passage of water and gases in and out of their bodies
Why is gas exchange a barrier to adapting to land?
- Gases are absorbed differently whether they are in air or dissolved in water
- organisms need a new system of gas exchange
Why is reproduction a barrier to adapting to land?
- aquatic organisms need water for reproduction
Why is buoyancy a barrier to adapting to land?
- water supports body tissues, air does not
- need supporting structures
Why are temperature fluctuations a barrier to adapting to land?
- land changes temperature much faster and much more drastically than water
Why are vision and hearing barriers to adapting to land?
- light and sound waves move differently through air and water
- organisms need to adjust vision and hearing
Why is mineral nutrition a barrier to adapting to land?
- water contains dissolved minerals for added nutrition
- since many aquatic animals are immobile, they need a way to supplement on land
Why is UV radiation a barrier to adapting to land?
- water filters UV light and protects life
- after the ozone layer was created, life could survive on land
Name the 8 barriers to adapting to land.
- UV radiation
- mineral nutrition
- sound and light
- buoyancy
- desiccation
- temperature fluctuations
- gas exchange
- reproduction
What prompted plants to move to land? Which were the first plants to do so?
- they are autotrophs. advantageous to grow in shallow waters, near light
- green algae (which evolved from cyanobacteria), appeared 0.75 Ga
What caused algae to evolve to forms that could survive entirely on land?
- Populations of algae were exposed to periods of drought.
- individuals which could tolerate extended periods of desiccation were selected
What are the biological lines of evidence for plants’ adaptations to life on land?
existing plant species had traits which predisposed them to being able to adapt to land
Name the plant adaptations to life on land (6)
1) in response to desiccation:
- developed the cuticle and multiple cell layers on the epidermis
- evolved roots
2) Gas exchange
- evolved stomata to allow gas to enter, could also be closed to prevent plant from drying out
3) Reproduction
- evolved spores that could survive desiccation, and eventually seeds
4) Buoyancy
- evolved structural support in the form of fibers and compounds
5) Temperature fluctuation
- traits evolved to prevent desiccation also helped them survive temperature fluctuations
- eventually evolved other methods to survive extreme weather
6) Mineral Nutrition
- roots allowed plants to get nutrients from soil
How long after plants did animals start moving onto land? Why?
30 - 100 MY
late silurian to early devonian
Before plants moved to land, there was no food for animals
When did the first land plants appear?
During the Ordovician
Which group of animals moved onto land first and why?
Arthropods moved onto land to escape predation during the Cambrian, but were not permanent terrestrial species.
By the Devonian (410-360 Ma), arthropods were present on land and their diversity increased rapidly
Which of our ancestors emerged from the water, and when?
- The Ichthyostega, a lobe-finned fish, emerged in the Late Devonian (370 Ma)
- it is the shared ancestor of all tetrapods
What were animal adaptations to desiccation?
1) Physical
- waxy coating
2) Behavioral
- living in damp habitats, at night
- concentrate waste
What were animal adaptations to gas exchange?
- in aquatic animals, gills have a membrane that o2 diffuses across
- in insects, small openings in exoskeleton keep membranes wet
- in vertebrates, small openings (trachea) and the lungs evolve
What was animals’ solution to reproducing on land?
internal fertilization
- prevents desiccation of ova and sperm
amniotic egg
viviparity
- egg retained in female after fertilization
How did eggs and animals’ behavior towards them change?
amniotic egg
- allows reptiles to lay eggs on dry land
fewer eggs produced
- burying eggs
- incubation response
What were animals’ adaptations in terms of buoyancy?
- arthropods: chitin exoskeleton
- vertebrates: cartilage and bone skeleton
- mollusks
calcium shell and hydrostatic skeleton
What were animals’ adaptations to temperature fluctuation?
development of strategies for thermoregulation
- homeothermy: ability to regulate body temp
–> metabolism: more energy, more food
–> behavior
How did animals’ ears and eyes change in response to their move to land?
- eyes become a sealed chamber filled with fluid
- ears became specialized to airborne wavelengths
Land colonization was only possible after …
the great oxygenation event
