3 The Cenozoic - Rise of Mammals

Question 1

End of dinosaurs and the K-Pg mass extinction

Answer 1

After 186 MY of dominance, dinosaurs disappear from fossil record 65.5MYA

Iridium - one of the most common elements in meteriotes —> meteorite impact killed the dinosaurs

Followed by ‘Compost Earth’

Question 2

Rise of Mammals

Answer 2

First eveolved 220MYA

‘Minor’ tax on until 65.5MYA —> K-Pg mass extinction saw large reptiles disappear - small mammals underwent radical increase in diversity

Question 3

What defines a mammal

Answer 3

1. Lactation
2. Middle ear with 3 bones
3. Jaw hinge
4. Fur

(other common characteristics —> placentation /endothermy — warm blooded)

Question 4

When do nearly all clades of mammals appear by

Answer 4

45 MYA

Question 5

Mammal faunas

Answer 5

Some areas have distinct mammal faunas

The faunas reflect how the planet looked 65MYA (distinct faunal areas include Eurasia-Africa-NA / SA / AUS / india / Madagascar)

- India + Asia 35MYA 
- NA + SA - 3MYA

Question 6

Great American interchange

Answer 6

Isthmus of Panama closure 3MYA - movement of land species in both direction but mostly north to south. 41% of SA mammals have evolutionary origin in North / Central American primates from south

Question 7

Plant metabolism and ecosystem changes in the oligocene - Oligocene environment

Answer 7

Lower atmospheric CO2 at 500ppm

Lower water availability —> lower CO2 availability - plants closed stomato to avoid stress

C4 metabolism evolution - more efficient at low CO2, high temperatures

Question 8

C4 metabolism - shifts photosynthesis from being a…

Answer 8

1 cell to a 2 cell system —> concentrates CO2 at the site of the key enzyme, rubisco

New leaf form - Kranz anatomy - each mesophyll cell adjacent bundle cell - more vascular tissue

Question 9

C4 clade of plants is ecologically and economically important

Answer 9

Warm season grasses and tropical grasslands rely on C5 metabolism

Many crop plants - maize, sorghum, sugar cane

1% plant species are C4 grasses - 30% of plant biomass

Eventually produced the grassland ecosystems of the tropics - rise of the Great African Herbivores

Question 10

Define a primate

Answer 10

1. Adaptations for tree climbing and brachiation
2. Rotating shoulder joint
3. A separate big toe / thumb
4. Stereoscopic vision - ability to see in 3D and perceive depth
5. Large brains
6. Claws into flattened nails
7. Typically 1 offspring per pregnancy
8. Upright bodies

Question 11

Primate evolution

Answer 11

Primates evolved in africa and later spread to Madagascar (lemurs radiation - SA (new world monkeys) but none in AUS and NA

Question 12

Madagascan lemurs

Answer 12

Madagascar separated from africa 150 MYA - populated later by various mammal taxa that then readjusted

Question 13

New world monkeys

Answer 13

First fossils - 35 MYA

Still uncertainty on the origins of new world monkeys

Found in the New world around 30 MYA (late Oligocene)

At the time new world monkeys arose the continents of South America and Africa had drifted apart

Question 14

Reproductive isolation for new and old world monkeys

Answer 14

Due to reproductive isolation, new world monkeys and old world monkeys underwent separate adaptive radiations over millions of years

New world monkeys - South America

Question 15

Africa

Answer 15

Miocene apes lived in dense forests

Approx 100 species of apes lived in this time

Cooling and drying of the climate/ Ape species returned to Africa

Earth movements produced the rift valley in Africa around 8MYA

Forests shrank and open habitats expanded

Miocene apes went into a big decline, but human ancestors were some of the Miocene apes who lived through these events.

Question 16

Human origins

Answer 16

Relationship of humans and apes was Darwins most controversial idea

Genome sequencing is clear - chimpanzees / Bononbos are our closest living relative

Question 17

‘Transitional form’ - Ardipithecus

Answer 17

Chimp / human ancestor skeletons in Ethiopia from 4.2MYA

Chimp like brain size / human like sexual dimorphism / foot and hand structure - bipedal

Question 18

Pattern of peopling

Answer 18

Genetic origins in Africa ‘Mitochondrial Eve’

Question 19

Reconstructing the past with aDNA (ancient DNA)

Answer 19

DNA preservation - dry, cold

Human remains in dry places: mammoths in very cold places - whole genome of extinct species

Doesn’t work for more than 1.8MYA

Question 20

aDNA fragmentation

Answer 20

aDNA is fragmented, damaged but can use massive parallel sequencing to obtain deep reads against a ‘modern’ polished scaffold

Question 21

3 Clades

Answer 21

1. Denisovians
2. Neanderthals
3. Modern Humans

Question 22

Neanderthal biology

Answer 22

Near complete genomes - mutations in melanocortin 1 receptor (MRC1) - likely to have pale skin and red/ginger hair

Shared mutations with H.sapiens in FOXP2 - language associates

Shared mutations with H.sapiens in TAS2R38 - can taste ‘bitter’

Question 23

100-300KYA H.sapiens, Neanderthals, denisovians

Answer 23

aDNA provides direct evidence that Neanderthals and denisovians interbred - hybrid individuals

Direct evidence of inbreeding - Neanderthals with excess himozygosity

Indirect evidence of Neanderthal-human interbreeding - modern genome 0-4% Neanderthal

Question 24

Macroevolution musings - Punctuated equilibrium dynamics (Darwin)

Answer 24

evolution as gradual accumulation of changes over long periods of time. Mutation rate (input for micro-evolutionary processes) is more or less constant, but macroevolutionary change is not

Question 25

Darwin was wrong about…

Answer 25

macroevolution and pattern follows punctuated equilibrium

Question 26

Punction and equilibrium

Answer 26

Periods of massive change (punction) and periods of relative statsis (equilibrium)

Question 27

Biological events

Answer 27

Evolution of photosynthess

Endosymbiosis (x2)

Hox gene duplications - jawed vertebrates

Evolution of vascular plants - oxygen, insects and mass extinctions

Flowering plants

Question 28

Some important mutations are very rare - so stochastic

Answer 28

Genome duplications - more Hox arrays / evolution of jawed vertebrates (took 100MYA)

Question 29

Long term evolution experiment - test of repeatability

Answer 29

Clone of E.coli - into 12 populations / same media, maintained in parallel

Passaged every 3 days for >30years (10,000 E.coli generations)