Evolution: Lecture 7

Question 1

What are fossils?

Answer 1

Preserved remnants (or traces) of past life in the physical world (rocks).

Question 2

What are the types of fossils?

Answer 2

– Mineral components
– Petrified organic material
– Casts
– Trace fossils (footprints etc)

Question 3

What do we get from fossils?

Answer 3

• Information about past ecosystems; climate; sea levels etc., & dating of geological record
• More direct view of evolutionary history than from living organisms

Question 4

Where are most fossils found?

Answer 4

Most fossils are found in sedimentary rock. This is found in the bottom of lakes and oceans.

Question 5

What is sedimentary rock composed of?

Answer 5

It is composed of layers building up, showing us the passage of time in that particular area.

• We find fossils in here as well which are preserved in the rocks. Things die and remains can be caught within the rocks.

Question 6

What are index/indicator fossils?

Answer 6

They are common, widespread fossils characteristic of particular periods of earth’s history. The fossils are the same in one area and another, therefore we can use it to determine histories. If we know that an organism existed at a particular time in one area and we observe to in a different area, we can make assumptions that they are there.

• Crucial for ‘relative dating’ in geological record.
• It works out how old rocks are and old sea levels, etc.

Question 7

What do fossils do?

Answer 7

They give us context to the age and order of species evolution.

Question 8

What is the geological record?

Answer 8

A standard time scale that partitions the Earth’s history into four eons and their subdivision of eras, periods, and epochs

Question 9

How old is the earth?

Answer 9

Earth is around 4.6 billion years old.

Question 10

When did microbial life arise?

Answer 10

3.5 billion years ago

• 3/4 of the earth’s time there has been active life.

Question 11

When were fossils of animals and plants common?

Answer 11

• Fossils of animals & plants common in the last ~550 million years: “Phanerozoic Eon”
• Phanerozoic divided into three ‘Eras’: Each Era subdivided into several ‘Periods’

Question 12

What are the eras in order from oldest to youngest?

Answer 12

Palaeozoic
Mesozoic
Cenozoic

Question 13

What was the last period of the palaeozoic era?

Answer 13

The last period of the palaeozoic era was the Permian period.

Question 14

What was the first and last periods of the mesozoic era?

Answer 14

The first was the Triassic period
The last was the Cretaceous period

Question 15

What are the first and most recent periods of the Cenozoic era?

Answer 15

The first is the Palaeogene period
The most recent is the Quaternary period.

Question 16

What was the geological record made using?

Answer 16

It was made using index fossils and specific dates were only figured out later.

Question 17

What happened when the geological record had abrupt changes?

Answer 17

When there were abrupt changes in the geological record (fossils) the period was deemed to have changed a lot. It was seen as VERY important.

Question 18

What are mass extinctions?

Answer 18

Many species extinct in very short time then replaced by new species.

Question 19

What are the causes of mass extinctions?

Answer 19

Causes: large environmental changes.

Plausible examples:
– Massive volcanic activity
– Impact by asteroid or comet

Question 20

Why are mass extinctions important?

Answer 20

They are of major importance in history. When a majority of life goes extinct, the biodiversity changes drastically.

• This is because only survivors can have speciation events and change.

Question 21

How many big extinctions were there?

Answer 21

There were 5 large ones: most of them marking the ends of eras/periods.

Question 22

End-Permian mass extinction?

Answer 22

Occurred 252 million years ago. The most devastating mass extinction.

• roughly 95% of all life in water went extinct.
• 90% of all species went extinct
• many large taxa went extinct (50% of Families)

Why did it occur? Hypothesized to be volcanic activity

Question 23

End-Cretaceous mass extinction?

Answer 23

~65 million years ago

• Most recent ‘big’ mass-extinction
• Extinction of ~50% of species on earth
  – e.g. dinosaurs (other than birds)
  – Several marine invertebrate groups

Question 24

What is adaptive radiations?

Answer 24

Rapid speciation and evolutionary change in underexploited habitats. The results are that many species come to be over a short period of time. There are a small number of competitors.

Two types: Regional and World-wide

Question 25

Regional Adaptive radiations?

Answer 25

Colonisation of new island chains

Question 26

World-wide adaptive radiations?

Answer 26

– Occur following mass extinction events.
– Only surviving lineages can radiate!
– Replacement in fossil record.

Question 27

Example: Hawaiian ‘Silversword alliance’?

Answer 27

Plant group, endemic to Hawaii
(very isolated, ‘young’ island group)

~50 species; great variation in size, shape

All descended from one species, in last ~5 million years.

Question 28

World-wide adaptive radiation of mammals after End-Cretaceous extinction?

Answer 28

Large land animals went extinct, smaller mammals adapted to become larger after the death of dinosaurs.

Question 29

How do complex adaptations evolve?

Answer 29

What ‘Darwinian’ evolution proposes:
– evolution through many small steps
– every ‘step’ should improve fitness.

Question 30

What is Gradualism?

Answer 30

New variants arose that were only slightly different, gradually changing. Each change had to improve fitness. It cannot be something that leads to eventual fitness, must be direct.

Question 31

Example of complex adaptations?

Answer 31

The camera eye is the type of eye that the giant squid has. It has a lens that opens and closes to adjust to the amount of light. It is moved by muscles to see different distances.

• Example of convergent evolution

Question 32

Mechanisms for evolution of complex adaptations?

Answer 32

1) Intermediates that are actually capable of functioning

2) Modification of existing structures with different functions

3) Larger ‘steps’ (than imagined by Darwin).
- Changes in developmental regulation
- Origin of novel genes, e.g. Gene duplication

Question 33

Intermediates that are actually capable of functioning?

Answer 33

Things that could be adaptations in their own right. In many cases, simpler forms of complex structures are functional.

– Evidence: Organs of different
complexity in related species
– Step-wise evolution plausible

Question 34

Modification of existing structures with different functions?

Answer 34

Changes from existing adaptations rather than from scratch. Involves exaptation

Question 35

Exaptation?

Answer 35

Structures adapted for one function are coincidently useful for another function.

Question 36

Example of Exaptation?

Answer 36

Feathers evolved in dinosaurs to be insulators as they are warm-blooded animals (like birds). Other feathers were used as display for communication between them.

• They don’t need barbules as they are just for thermoregulation or display. They could also be used to “glide” as a flight surface.

Question 37

The evolution of developmental regulation?

Answer 37

• Mutations affecting genes that control development
• Small genetic change can result in large, coordinated changes in phenotype.

Question 38

Example of Developmental Regulation? Homeotic genes?

Answer 38

Hox genes: control the identity of segments along developing animal body.

Wild fruitfly = one set of wings
Homeotic mutant = two sets of wings as one segment takes the identity of the other.

Question 39

New genes (gene duplication)?

Answer 39

At a part of the chromosome there is a gene duplication event. Over time, independent evolutionary change occurs where one can acquire a new function.

Question 40

What are paralogs?

Answer 40

Two related genes in one genome.

Question 41

Example of globins by gene duplication?

Answer 41

• Gene duplication – resulting in ancestral genes for Hemoglobin
  subunits & Myoglobin
• Later gene duplication, resulting in α- and β- globin gene families