Lec 8: Diversification - Moving onto land

Question 1

What is life like during the Proterozoic?

Answer 1

• no life on land
• photosynthesis evolves
• eukaryotes evolve
• bacterial mats grow fast

Question 2

What happens at the beginning of he Proterozoic?

Answer 2

the great oxygenation event

Question 3

What was life like during the Cambrian?

Answer 3

• shells and hard bodies dominate
• animals become more motile
• explosion of new body types in animals
• first chordate (pikaia), ancestor of all vertebrates

Question 4

What was life like during the Ordovician?

Answer 4

• first vertebrates evolve from Pikaia

- complex animals and plants have evolved, but have not left the water

Question 5

Why is desiccation a barrier to adapting to land?

Answer 5

• 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

Question 6

Why is gas exchange a barrier to adapting to land?

Answer 6

• Gases are absorbed differently whether they are in air or dissolved in water
• organisms need a new system of gas exchange

Question 7

Why is reproduction a barrier to adapting to land?

Answer 7

• aquatic organisms need water for reproduction

Question 8

Why is buoyancy a barrier to adapting to land?

Answer 8

• water supports body tissues, air does not

- need supporting structures

Question 9

Why are temperature fluctuations a barrier to adapting to land?

Answer 9

• land changes temperature much faster and much more drastically than water

Question 10

Why are vision and hearing barriers to adapting to land?

Answer 10

• light and sound waves move differently through air and water
• organisms need to adjust vision and hearing

Question 11

Why is mineral nutrition a barrier to adapting to land?

Answer 11

• water contains dissolved minerals for added nutrition

- since many aquatic animals are immobile, they need a way to supplement on land

Question 12

Why is UV radiation a barrier to adapting to land?

Answer 12

• water filters UV light and protects life

- after the ozone layer was created, life could survive on land

Question 13

Name the 8 barriers to adapting to land.

Answer 13

• UV radiation
• mineral nutrition
• sound and light
• buoyancy
• desiccation
• temperature fluctuations
• gas exchange
• reproduction

Question 14

What prompted plants to move to land? Which were the first plants to do so?

Answer 14

• they are autotrophs. advantageous to grow in shallow waters, near light
• green algae (which evolved from cyanobacteria), appeared 0.75 Ga

Question 15

What caused algae to evolve to forms that could survive entirely on land?

Answer 15

• Populations of algae were exposed to periods of drought.

- individuals which could tolerate extended periods of desiccation were selected

Question 16

What are the biological lines of evidence for plants’ adaptations to life on land?

Answer 16

existing plant species had traits which predisposed them to being able to adapt to land

Question 17

Name the plant adaptations to life on land (6)

Answer 17

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

Question 18

How long after plants did animals start moving onto land? Why?

Answer 18

30 - 100 MY
late silurian to early devonian
Before plants moved to land, there was no food for animals

Question 19

When did the first land plants appear?

Answer 19

During the Ordovician

Question 20

Which group of animals moved onto land first and why?

Answer 20

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

Question 21

Which of our ancestors emerged from the water, and when?

Answer 21

• The Ichthyostega, a lobe-finned fish, emerged in the Late Devonian (370 Ma)
• it is the shared ancestor of all tetrapods

Question 22

What were animal adaptations to desiccation?

Answer 22

1) Physical
- waxy coating

2) Behavioral
- living in damp habitats, at night
- concentrate waste

Question 23

What were animal adaptations to gas exchange?

Answer 23

• 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

Question 24

What was animals’ solution to reproducing on land?

Answer 24

internal fertilization
- prevents desiccation of ova and sperm

amniotic egg

viviparity
- egg retained in female after fertilization

Question 25

How did eggs and animals’ behavior towards them change?

Answer 25

amniotic egg
- allows reptiles to lay eggs on dry land

fewer eggs produced

• burying eggs
• incubation response

Question 26

What were animals’ adaptations in terms of buoyancy?

Answer 26

• arthropods: chitin exoskeleton
• vertebrates: cartilage and bone skeleton
• mollusks
  calcium shell and hydrostatic skeleton

Question 27

What were animals’ adaptations to temperature fluctuation?

Answer 27

development of strategies for thermoregulation
- homeothermy: ability to regulate body temp

–> metabolism: more energy, more food

–> behavior

Question 28

How did animals’ ears and eyes change in response to their move to land?

Answer 28

• eyes become a sealed chamber filled with fluid

- ears became specialized to airborne wavelengths

Question 29

Land colonization was only possible after …

Answer 29

the great oxygenation event