3 The Cenozoic - Rise of Mammals Flashcards
End of dinosaurs and the K-Pg mass extinction
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’
Rise of Mammals
First eveolved 220MYA
‘Minor’ tax on until 65.5MYA —> K-Pg mass extinction saw large reptiles disappear - small mammals underwent radical increase in diversity
What defines a mammal
- Lactation
- Middle ear with 3 bones
- Jaw hinge
- Fur
(other common characteristics —> placentation /endothermy — warm blooded)
When do nearly all clades of mammals appear by
45 MYA
Mammal faunas
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
Great American interchange
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
Plant metabolism and ecosystem changes in the oligocene - Oligocene environment
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
C4 metabolism - shifts photosynthesis from being a…
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
C4 clade of plants is ecologically and economically important
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
Define a primate
- Adaptations for tree climbing and brachiation
- Rotating shoulder joint
- A separate big toe / thumb
- Stereoscopic vision - ability to see in 3D and perceive depth
- Large brains
- Claws into flattened nails
- Typically 1 offspring per pregnancy
- Upright bodies
Primate evolution
Primates evolved in africa and later spread to Madagascar (lemurs radiation - SA (new world monkeys) but none in AUS and NA
Madagascan lemurs
Madagascar separated from africa 150 MYA - populated later by various mammal taxa that then readjusted
New world monkeys
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
Reproductive isolation for new and old world monkeys
Due to reproductive isolation, new world monkeys and old world monkeys underwent separate adaptive radiations over millions of years
New world monkeys - South America
Africa
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.
Human origins
Relationship of humans and apes was Darwins most controversial idea
Genome sequencing is clear - chimpanzees / Bononbos are our closest living relative
‘Transitional form’ - Ardipithecus
Chimp / human ancestor skeletons in Ethiopia from 4.2MYA
Chimp like brain size / human like sexual dimorphism / foot and hand structure - bipedal
Pattern of peopling
Genetic origins in Africa ‘Mitochondrial Eve’
Reconstructing the past with aDNA (ancient DNA)
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
aDNA fragmentation
aDNA is fragmented, damaged but can use massive parallel sequencing to obtain deep reads against a ‘modern’ polished scaffold
3 Clades
- Denisovians
- Neanderthals
- Modern Humans
Neanderthal biology
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’
100-300KYA H.sapiens, Neanderthals, denisovians
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
Macroevolution musings - Punctuated equilibrium dynamics (Darwin)
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
Darwin was wrong about…
macroevolution and pattern follows punctuated equilibrium
Punction and equilibrium
Periods of massive change (punction) and periods of relative statsis (equilibrium)
Biological events
Evolution of photosynthess
Endosymbiosis (x2)
Hox gene duplications - jawed vertebrates
Evolution of vascular plants - oxygen, insects and mass extinctions
Flowering plants
Some important mutations are very rare - so stochastic
Genome duplications - more Hox arrays / evolution of jawed vertebrates (took 100MYA)
Long term evolution experiment - test of repeatability
Clone of E.coli - into 12 populations / same media, maintained in parallel
Passaged every 3 days for >30years (10,000 E.coli generations)
