Cambrian Explosion Flashcards
Examples of fossil records
- Partial or complete remains (e.g. bones, shells)
- Traces (e.g. footprints, “shadows”
How is preservation biased (4)
- Hard parts preferred over soft
- Abundant species preferred
- Long-lived species preferred
- Large geographical range
When was the first multicellular eukaryotic organism and 1st multicellular organism w/sexual reproduction
~2.1-1.8 bya
1.2 bya (small algae)
Three theories behind multicellularity
Symbiosis, cellularisation, coloniality
Problem with symbiosis
Would require fused genomes of two species into one
Problem with cellularisation
No known example
Problem with coloniality
Many colonial protists, some with cell specialisation
5 requirements to be animal
- Multicellular
- Eukaryotic
- Heterotrophic
- Structural proteins (e.g. collagen), nerve & muscle cells
- Unique sequence of development, regulated by Hox genes
What was the earliest evidence of bilateral symmmetry
Doushantuo microfossils
- aquatic, microscopic multicelllar organisms
- lived 635-551 mya
What was the earliest known large multicellular organism
Ediacaran fauna
- lived 600-542 mya
- discovered in 1947 in ediacara hills
- occur around world
What happened to ediacaran legacy
Preservation bias
Predation
Competition
Change in environmental conditions
Describe Cambrian explosion
- Modern animal phyla appear in fossil record suddenly, dramatically and simultaneously
- All major body parts
- Hard body parts
- All 35 living phyla (+a few more)
Why did animal life appear so suddenly
- Threshold oxygen lvls crossed
- Nutrient lvls may have risen, increasing primary productivity & therefore consumer productivity
Ecological reasons for why animals diversify so quickly
- New niches arose w/evolution of animals
- Predation led to selection for increased size
Geological reasons why animals diversify so quickly
- Active metabolism possible w/oxygen availability opened new ways of life
- Supportive collagen can only be formed in presence of o2
