Lecture 2: Origin of complexity. 1. Eukaryotes What are they? When do they evolve? When do they diversify? Evolution and the atmosphere 2. Metazoans What are they? Phylogenetic tree Evolution and preservation 3. The Ediacaran fauna 4. The appearance of hard parts
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What are they?
When do they evolve?
When do they diversify?
Evolution and the atmosphere
What are they?
Evolution and preservation
3. The Ediacaran fauna
4. The appearance of hard parts
5. Events at the base of the Cambrian
Large (about 100 mm),
Small (about 10 mm),
May use oxygen
Probably by endosymbiosis
DNA evidence around 3.8 Ba
Oldest fossil 2.1 Ba
Are both dates correct?
1.3 When do they radiate?
Fossils common after 1 Ba
Fauna dominated by acritarchs
Diversity peak at 700 Ma, then decline
1.4 Relationship to environment
Eukaryotes obligate aerobes
Free oxygen in atmosphere and ozone shield after 2 Ba
?Critical O2 level passed sometime in late Proterozoic?
Metazoans are multicelled animals
Molecular clocks record origin
Fossil evidence suggests origin in late
Precambrian, around 600 Ma
Most about 550 Ma, global distribution,
Cyclomedusa – a probable jellyfish with a pelagic mode of life.
Probably an ancestral arthropod, with a rudimentary head.
A problematic organism with three-fold symmetry not seen in modern animals.
Depending on your perspective, this is a worm, a soft coral or a completely extinct representative of a group of quilt-like animals, the Vendozoa.
Happened at or near 543 Ma
Defines the Precambrian/Phanerozoic boundary
Increases preservation potential many fold,
and hence quality of fossil record.
Diversity appears to increase here -
is this real or an artefact?
Skeletons are useful for
- increasing potential size
- increasing potential speed
- protection from predation