Lecture 26: Macroevolution part 3: Extinction

Question 1

Phanerozoic

Answer 1

• 5 major extinction episodes happened during the phanerozoic

-20-55% of families went extinct and 60-95% of species we extinct in 1 million years

Question 2

Mass extinctions (3)

Answer 2

-Global events

-Involve a wide rand of organisms

-Rapid relative to expected lifespan of taxa (ie they happen too fast)

Question 3

Causes of mass extinction (4)

Answer 3

-Global decrease in habitat quality and extent resulting from asteroid impact or tectonic plate movement

-results in temperature chamges and glaciation

-Changes atmospheric and oceanic composition

-Direct habitat loss (ex loss of shallow water bc it freezes or loss of high elevation bc O2 levels drop)

Question 4

Mass extinctions vs all extinctions

Answer 4

-Mass extinctions only account for 4% of all extinctions during the Phanerozoic Eon

-the other 96% occurred at normal rates as taxa with restricted ranges and limited dispersal are more likely to go extinct

Question 5

The terminal-ordovivian mass extinction (4)

Answer 5

-Lost 60% of marine genera

-25% of marine families including over 1000 marine invertebrates

-444 MYA

-Caused by the glaciation of southern supercontinent Gondwana which lowered the sea level, drastically reducing the continental shelf habitat

Question 6

The Permian-Triassic mass extinction (4)

Answer 6

-Happened at the end of the Paleozoic (251 MYA)

-The biggest extinction ever

-lost 90-95% of marine species and 70% of terrestrial verts over a few million years

-Normal levels of biodiversity did not recover for another 6 million years

Question 7

Causes of the permian-triassic mass extinction (3)

Answer 7

1. Glaciation on Gondwana resulting in global cooling and lowering sea level
2. Reduction of shallow continental shelf habitat due to Pangea formation
3. Large volcanic eruptions in what is now Siberia sent ash clouds and large amounts of sulfate into the air

Question 8

The Cretaceous-Paleogene (K-PG) mass extinction (4)

Answer 8

-Happened at the end of the mesozoic (65MYA)

-Many marine inverts went extince

-Non-avian dinos, pterosaurs and large bodied marine reptiles were WIPED OUT

-Evidence that a huge (10-15 Km WIDE) asteroid his the earth

Question 9

Evidence for the asteroid impact of the K-PG (3)

Answer 9

-High concentration of iridium at K-Pg boundary

-Iridium rare in Earth’s crust but abundant in extra-terrestrial objects

-massive crater 180km found in the 1990s was dated to 65 MYA

Question 10

How the K-PG asteroid killed everything (6)

Answer 10

-It hitting the ocean ejected material considerable distances

-Liquid vaporized water and SO2 ejected into the atmosphere, forming sulfuric acid causing acid rain

• SO2 also scatters solar radiation leading to global cooling and darkness

-Impact created widespread wildfires

-Impact created massive earthquakes, contenental landslides and set off volcanoes

-Impact caused a massive 4km tall tidal wave

Question 11

How plants survived (3)

Answer 11

-Leaves or whole branch systems that can wilt or be shed during periods of drought

• ability to die back to the ground and survive from one growing season to next as underground stems or rhizomes
• lie dormant during periods of adverse weather, survive for long periods of
  time in seed banks

Question 12

Is there another mass extinction going on rn? (3)

Answer 12

• in the big 5 extinctions, 50-90% of taxa went extinct however since the 1600s less than 1% of taxa have gone extince

-But current extinction rate is estimated to be 100-1000x greater than the background rate

-most loss attributed to human activity like colonization, habitat loss, and expanding human populations