Cambrian explosion Flashcards
What occurs between the Ediacaran and the Cambrian?
A step up in phyla and classes (Cambrian explosion)
What is there very little of after the Cambrian?
Existence of new phyla and classes (inhibited by hard fossil bias)
How is the Cambrian divided?
Into stages due to their being no formal recognition of the boundaries
What is the main difference between the Ediacaran and present day environments?
No life in the upper water column or within the sediment
What is Cloudina?
Present on the boundary between Ediacaran and Fortunian it is the earliest mineralising organism (worm like)
What is couldina a precursor?
To small shelly fauna which diversify in Cambrian stage 2 (Tommotian)
What are some examples of ‘small shelly fossils’?
Stem brachiopod
Problematica
Palaeoscolid worm
What are examples of fauna from Chenjiang China?
Anomalocaris
Arthropods
What fauna are an indicator of the Cambrian explosion?
Domination of arthropods
What formation occurred after Chenjiang?
Sirius Passet - Greenland
What is the boundary like at Sirius Passet?
An unconformity between stage 3 Cambrian and the Upper most Ediacaran
What fossils are present at Sirius Passet?
Microbial mat trace fossils
What fauna are present in the Sirius Passet?
Anomalocarids
Palaeoscolecids
Vetulicolians
Halkieria
What is the anomalocarid thought to be have been like in the Sirius Passet?
A filter feeder of plankton
What are the 2 taphonomy types in Siriuspasset?
Typical Sirius Passet preservation
Burgess shale type
What is preservation like with the typical Sirius Passet preservation?
Fauna mainly articulated
Mouldic
Infauna very rare
3D gut contents and body axes
Easily decomposed tissues not preserved (or not well-preserved)
No size limitations on preservation
What is Burgess shale type preservation like?
Preservation as carbon/clay films
Fauna preserved sub-parallel to
bedding
What formation occurred after Siriuspasset?
Emu Bay - South Australia
What has one of the oldest records of with arthropods in Emu Bay?
Eyes
What rock sequence formed after Emu Bay?
Burgess shale - British Columbia Canada
What was the relative abundance of species in the burgess shale?
33% Arthropoda
22% Porifera
14% Algae
15% others
How much were arthropods of relative abundance of species in the burgess shale?
60%
What is the relative abundance of different lifestyles in the Burgess shale?
Epibenthic 64% (just above or on sediment)
Endobenthic 13%
Nektobenthic 12% (water column above sediment)
11% Nektonic (upper water column)
What is the simplified burgess shale food web split into?
Active predators
Scavengers
Grazers and filter feeders
Algae
What happens to the sediment as life progressed through the stages of the Cambrian?
The sediment geochemistry changes as it is exposed to oxygen (substrate revolution)
How are hopeful monsters produced?
When genome duplication occurs producing redundant genes
What evidence of the first predators are there?
Holes on the exterior of Cloudina showing shift from microbial mat to predation
How are Uranium, Oxygen and Carnivorous fauna related?
Increased uranium in sediment record shows greater oxygen in environment which is needed for predation and increased activity
How did oceanic ventilation occur?
Development of Eukaryotic bacteria created mixing of a ‘stagnant’ ocean full of cyanobacteria
What are O2, Nutrients and substrate mobility like as you transition from land to sea?
All have greatest concentration near shore and decrease as distance form shore increases
What happened that created high energy environments in the Cambrian?
Flooding creating high energy pools which might have had enough energy for diversification
Why is it thought calcium shells were first developed?
Calcium is toxic so to get rid of a waste product
