Cambrian explosion

Outline the potential drivers of the Cambrian explosion.

What experienced major diversification and when?

Marine taxa at high taxonomic levels, 541-530 Ma

What did the diversification of marine taxa mean?

rapid expansion of phyla and classes

What occurred in the Cambrian explosion?

• Increase in skeleton/ shell-secreting organisms

• Diversification and complexation of animals

Cloudina

Earliest mineralising organism; tube-shaped fossil; fossils from Ediacaran

What are Cloudina a precursor for?

small shelly fauna that diversify in Cambrian stage 2

Trace fossils…

… rose in numbers

Reasons for apparent low diversity before

• no hard parts and poor preservation

• lack of rock record

Reason for low diversity before

• lack of O2 in deep ocean (lack of habitable environments) → not enough oxygen to diversify and live complex lives

• snowball earths

Why apparent high diversity after?

• hard parts evolved → more preservation

• more complex rock record

Reasons for high diversity (6)

• Build up of oxygen increased habitable seafloor

• end of snowball earth and transgression of shallow seas onto continental masses

  → very habitable

  → shallow seas great for diversifying life

• tectonics increase nutrient flux to oceans (increased weathering and erosion of continental rock)

• skeletons evolved due to increased predation pressure

• more oxygen increased metabolic yield → increased complexity (could grow skeletons)

• mat grazing cleared seafloor → diversification

what was the cause of the oxygen increase? (4)

• enhanced nutrient supply and carbon burial

• ecosystem engineering species - sponges (consuming dissolved organic carbon)

• greening land surface

• atmospheric oxidation in late Neoproterozoic with delayed ocean oxygenation in Cambrian