Ediacaran Biota Flashcards
The Cambrian explosion is said to data the start of modern life on Earth
Is there any evidence of life before this
- There was a highly enigmatic and diverse assemblage of fossils which emerged, flourished, and died out between ~600 and 540Mya
- This biota predates the Cambrian explosion but occurs after ‘Snowball Earth’ (Cryogenian)
- Occured in the Ediacaran period
What was the biota like in the Edicaran Period
- Characterised by sparse and very distinctive soft bodied (presumed marine) biota
- Comprising mainly frond-like and tubular organisms
- Largerly sessile (i.e. attrached and immobile)
- Most common Ediacaran taxa resemble bags/sacs, discs, fronds or segmented worms
Here is a map which shows where Ediacaran Biota fossil have been found
What is the issue with looking at this distribution
Continental configuration was very different to the present one, back in Ediacaran times
What is special about the Ediacaran Biota
- Edicaran Biota represents the first definite complex multiceullar organism with specialised tissue on the planet
- They apparently underwent an evolutionary burst at the Avalon Explosion (~575Ma)
Ediacaran biota became extinct closr to the start of the Cambrian explosion
Is there a reason for this?
- Perhaps the demise was due to new taxa outcompeting these older organisms, environmental change and predations
- It may gave been a failed evolutionary experiment with later multicellular life evolving independently - no apparent relationship with subsequent biotas
There are three distinct Ediacaran fossil association have been recognised
What are they?
- 580 to 575Ma - the Avalon biota
- 560 to 555Ma - the White Sea Biota
- 550 to 542Ma - the Nama assemblage
What was the name of the first macrofossil ever recorded from rocks of unequivocal Precambrian age
Charnia
Ediacaran biota record a transition from a global biota dominated by microscopic organisms, to a Cambrian world literally swarming with animals
What are the reasons suggested about why the Ediacardan Biota Emerge?
- The emergence from Snowball Earth allowed the release of high levels of oceanuc nutrients
- Oxygen began penetrating deeper into oceans and build up in the atmosphere
- The Rodinia supercontinent was riting apart, which caused substantial volcanic activity, nutrient production and creation of shallow seas, which created ideal conditions for new life to thrive
What are Microbial mats and how did they aid the first mobile organisms in the latest Edicaran times
- Microbial mats: associations of bacteria and other microorganisms covered the seafloor in a contineous manner
- These mats became a food source of the first mobile organisms
- Some of the bacteria in the mats helped to preserve the soft-bodied Ediacaran organims through coating thek in sulphide minerals
Why is it believed that Ediacaran biota have no relationship with any living organisms
Because the overall evolutionary relationships are so obscure, many researchers believe that Ediacaran biota has no relationship with any living organisms
If they left no descendants, they can be viewed as ‘failed evolutionary experiment - cannot relate to modern phylogentic groups
Because there is no genetic tree to modern organisms, three Ediacaran assemblages where made
What is suggested by the Avalon assemblages
Is defined at Mistaken Point, Newfoundland, Canada and is dominated by long-ranging deep water rangeomorphs, interpreted as filter feeders
What were the White Sea assemblage
represents the peak in diversity and is followed by a mass extinction
What were the Nama assemblage
Is named after Namibia where the fossils are not diverse, but well-preserved (preservational biases could be responsible)
They are thought to have lived in shallow water microbial mats
It includes many organic-walled tubular organisms, trace fossils, and the first calcifuing invertebrates (worm-world)
What are the 4 main theories for the extinction of the overwhelming majority of Edicaran taxa at the Precambria boundary
What are they?
- Competition from other organisms
- Grazing/Predation
- Environmental change
- Preservation (and sampling bias)
How is it suggested Ediacaran biota have died out through Grazing/Predation
Some existing Ediacaran forms, plus new grazing organisms which evolved in the Cambrian explosion, degraded, destabilised and/or destroyed the microbial mats that many Ediacaran organisms depended on
Alternatively, animals with exoskeletons which evolved in the Early Cambrain could have predated the relatively defenceless Ediacaram biota
