1.2 Introduction into mammals and evolution Flashcards
What are the geological timescales defiend by?
What are the geollogical timescales (learn this and you have basically learnt everything) - keep drawring it out
• Defined by changes in flora and fauna which are in turn influenced by global events, which in turn influenced by global events and tectonic plates - the continental drift of tectonic plates
Continental drift: tectonic plates
When was the Earth formed?
What is it formed off?
What do the junctions between the moving plates cause?
At what rate are these plates moving?
The surface of the earth is divided into tectonic plates (French map) shows the known tectonic plates that divide the surface of the earth. The Earth formed about 4.5 billion years ago – it’s a solid outer crust floating on molten layer. The molten layers below the plates have convection currents run through them – those convection currents drive the plates – junctions between the plates moving – subduction one under the driver. This causes things like Earth quakes and vulcanism
These plates are moving about the same rate fingernail grows – whole surface of the earth changes dramatically – over thousands of years the whole surface of the earth has changed dramatically
Late Proterzoic
How many million years ago?
What were the key features at this time?
- -at this time polar region is frozen over, polar ice capes come and go over geological time
- -We haven’t got a great deal of land mass most of the globe is covered in sea – the pan-african and panthalassic ocean. You can see in the white outlines the continents that we see today .
- -No complex life at this time.
Cambrian explosion – ‘explosion of life’
How many million years ago?
What were the key features at this time?
What is the cambrian explosion thought of now?
What funa showed that there were multicellular organisms before?
What examples of things we recognize today date back to the cambrian?
What happens to rocks from this time?
This is a period which we see an explosion of multicellular life. The Cambrian explosion is now described as a little bit of an artefact – in recent years multi-cellular fossils have been found which pre-date the Cambrian this whole funa called the: Ediacaran fauna – almost jelly like multiple cellular organisms that don’t fossilise very well because there isn’t any hard parts, named after a mountain range in Australia but such fossils also occur in the UK – massive groups of organisms that is now better known in the fossil record that pre-dates the Cambrian explosion but now nothing like them exists [all extinct] because during the Cambrian we see the appearance of things we recognize today such as molluscs and arthropods
The geological timescale and continental movement the surface rock is constantly being destroyed and recycled again, really old rocks get broken down and recycled again.
Late Cambrian
How many million years ago?
What were the key features at this time?
514 mya
Beginning of the Palaeozoic Era
• First multi-cellular organisms and invertebrates appeared during the Cambrian, 500-570 mya, the so-called
Late Cambrian (cont)
How many million years ago?
What were the key features at this time?
- Pikaia (sub phylum Cephalochordata)
- Burgess Shale in British Columbia
- Originally classified by Walcott as a polychaete
- Reclassified by Simon Conway Morris as a chordate, based on primitive notochord
Middle Ordovician
How many million years ago?
What were the key features at this time?
- Increase in land mass – still predominately ocean land masses, climate change going on still
- Ancient oceans separated the barren continents of Laurentia, Baltica, Siberia and Gondwana
- The end of the Ordovician was one of the coldest times in Earth history; ice covered much of the southern region of Gondwana survive today (lampreys and hagfish)
Middle Silurian
How many million years ago?
What were the key features at this time?
- Continents begin to collide as Paleozoic Oceans close
- Laurentia (north) collides with Baltica, closing the northen branch of the Iapetus
Ocean and forming the ‘Old Red Sandstone’ continent (Scotland Highland Boundary Fault)
• Coral reefs are predominant expand and land plants begin to appear – you can find really good fossilized sea bed
Early Devonian
How many million years ago?
What were the key features at this time?
Give an example?
- The Age of Fish!
- By the Devonian [age of the fishes] the early Paleozoic oceans were closing, forming a ‘pre-
- Pangea’ now moving into a time that is important for mammal evolution
- Freshwater fish were able to migrate from the southern hemisphere continents to North America and Europe
- Forests grew for the first time in the equatorial regions of Artic Canada
- First bony fish appeared, about 390 mya
- First Tetrapods (amphibians) also appeared during the Devonian, about 350 mya
- Ichthyostega was an early example
Late Carboniferous
How many million years ago?
What were the key features at this time?
Late Carboniferous (306 mya)
• Pangea begins to form during Early Carboniferous
- During the Early Carboniferous the Paleozoic oceans between Euramerica and Gondwana began to close, forming the Appalachian and Variscan Mountains
- Ice cap grows at the South Pole
- Four-legged vertebrates evolve in the great coal swamps near the Equator
- First reptiles and insects appear, about 280-320 mya.
- By the Late Carboniferous the continents that make up modern North America and Europe had collided with the southern continents of Gondwana to form the western half of Pangea
- Ice covers much of the southern hemisphere and vast coal swamps formed along the equator
Late Permian
How many million years ago?
What were the key features at this time?
(255 mya)
- Vast deserts covered western Pangea during the Permian as reptiles spread across the face of the supercontinent
- Mammal-like reptiles emerge and dominate the Permian, the earliest amniote ancestors of mammals (see later lectures)
- In the mid-Permian pelycosaurs are replaced by therapsids
End Permian extinction
What percentage of marine species went extinct? and what percentage of terrestrial vertebrates?
- At the end of the Permian was greatest extinction of all time; an estimated 96% of marine species and 70% of terrestrial vertebrates became extinct
- The formation of Pangaea, causing a clear loss of large areas of continental shelf ecosystem, may have been a factor, although other causes (vulcanism, bolide impact, methane release from sea floor) have been implicated
- This may have been exacerbated by the sea level dropping, due to midoceanic ridges collapsing, further reducing the amount of continental shelf habitat
Early Permian mammal-like reptiles
What is the example?
Dimetrodon (Order Pelycosauria, sub-class Synapsida)
Most died out at the end permian extinction
Late Permian mammal-like reptiles
What is the example?
Dicynodon (Order Therapsida) these are most advanced on the earlier pelycosauria
Early Triassic
How many million years ago?
What were the key features at this time?
- Dinosaurs emerged in the late Permian, and ruled through the Triassic and Jurassic ‘age of reptiles’
- However, mammal-like reptiles were hanging on… (eg Thrinaxodon)
- … and by the late Triassic, early Jurassic, early mammals are on the scene (eg Megazostrodon)
- At the end of the Triassic, Pangea began to rift apart
- The supercontinent of Pangea, mostly assembled by the Triassic, allowed land animals to migrate from the South Pole to the North Pole
- Life began to re-diversify after the great Permo-Triassic extinction, and warm-water faunas spread across Tethys
Thrinaxodon (Order Therapsida)
They got smaller and were doing well in the background on the dinosaurs, it took a while for things to recover
Even by the Triassic we got what we would define as a mammal artist impression
Late Jurassic
How many million years ago?
What were the key features at this time?
152 MYA
All the continents joing up to form pangea, duriing the mezasoic all of these land masses were seperating this is a crucial trend that effect mammal evolution right up till today
We will be spending time looking at the living mammals effect
- Birds first appear in the Jurassic period (eg Archaeopteryx)
- In the Early Jurassic, dinosaurs spread across Pangea
- By the Early Jurassic, south-central Asia had assembled; wide Tethys Ocean
separated the northern continents from Gondwana
• Though Pangea was intact, the first rumblings of continental break up could
be heard…
- … and in the Middle Jurassic the supercontinent of Pangea begins to break apart
- By the Late Jurassic the Central Atlantic Ocean was a narrow ocean separating Africa from eastern North America
- Eastern Gondwana had begun to separate form Western Gondwana
Late Jurassic
Example?
Megazostrodon (Subclass Prototheria) well known fossil – egg laying mammal
KT boundary
What event took place?
Where was it?
(66 mya)
- Impact of a 10 mile wide comet at Chicxulub (gulf of Mexico) causes global climate changes that killed the dinosaurs and many other forms of life
- By the Late Cretaceous the oceans have widened, as India approaches the southern margin of Asia
