1. AP Biology – Lecture #4
Big Idea #1 – Life continues to evolve within a changing environment
Adapted from Rebecca Rehder Wingerden ©

2. Speciation and extinction have occurred throughout the Earth’s History.
Speciation rates can vary, especially when adaptive radiation occurs when new habitats become available.
Monotremes
(5 species)
Ancestral
mammal
Ancestral
Cynodont
Marsupials
(324 species)
Eutherians
(5,010 species)
MYA
Adaptive radiation of mammals: Fossil evidence indicates that mammals underwent a dramatic adaptive radiation after the extinction of terrestrial dinosaurs 65.5 mya. Although mammals originated about 180 mya, the mammal fossils older than 65.5 mya are mostly small and not morphologically diverse.

3. Speciation and extinction have occurred throughout the Earth’s History.
b. Species extinction rates are rapid at times of ecological stress. • Five major extinctions (mass extinctions)

4. Speciation and extinction have occurred throughout the Earth’s History.
Ordovician-Silurian mass extinction
(443 mya): Third largest extinction,
85% of sea life was wiped out. An ice
age has been blamed for the
extinctions - a huge ice sheet in the
southern hemisphere caused climate
change and a fall in sea level, and
messed with the chemistry of the
oceans.
Late Devonian mass extinction
(359 mya) Three quarters of all
species on Earth died out. Life
in the shallow seas were most
affected. Changes in sea level,
asteroid impacts, climate change
and new kinds of plants messing
with the soil have all been blamed
for these extinctions.

5. Speciation and extinction have occurred throughout the Earth’s History.
Permian mass extinction (248 mya)
Nicknamed The Great Dying, 98% of
species died out. Proposed causes;
asteroid impact, flood basalt eruptions,
catastrophic methane release, a drop in
oxygen levels, sea level fluctuation or
some combination of these. Marine
creature were affected and insects
suffered.
Triassic-Jurassic mass extinction
(200 mya) Roughly half of all the
species became extinct. Climate
change, flood basalt, eruptions and
an asteroid impact have all been
blamed for this loss life. Many types
of animals died out, including
marine reptiles, some large
amphibians, and large numbers of
cephalopod mollusks. Strangely,
plants were not so badly affected.

6. Speciation and extinction have occurred throughout the Earth’s History.
Cretaceous-Tertiary mass extinction
(65 mya) Also known as the K/T
extinction - is famed for the death of
the dinosaurs. It’s suggested that the
decline was due to flood basalt
eruptions affecting the world’s climate,
combined with drastic falls in sea level.
There is also evidence of a huge
asteroid or comet hitting the seabed
near the Yucatan Peninsula in Mexico.

7. Speciation and extinction have occurred throughout the Earth’s History.
Human impact on ecosystems and species extinction rates:
Is a sixth mass extinction underway?

8. Speciation and extinction have occurred throughout the Earth’s History.
Bozeman Biology: Speciation and Extinction (13:00 min.) speciation-and-extinction
Nova: Last Extinction Megabeasts’ Sudden Death (53:00 min.)