Lecture 5: The Cambrian Explosion Flashcards
The Ediacaran saw the arrival of…
Bottom dwellers (on the sea floor), e.g cyanobacteria and sponges.
Mobile multicellular animals, e.g heterotrophic browsers and grazers
First mineralised hard parts appear, e.g cnidarians
Arthropods (first pelagic (swimming) animals, trilobites and crustacea)
As we move into the Precambrian (~530 Ma)…
The ‘small shelly fauna’
= greater diversity
tiny (few mm) molluscs, brachiopods arrived with hard parts much more easily fossilized
Why did mineralisation occur/ origins of the skeleton?
Rising O2 and changing seawater chemistry
Larger body size needed support
Hardened excreted waste Ca?
What was common in the early Cambrian ecosystem?
shelly faunas
molluscs, brachiopods, echinoderms, arthropods
soft bodied animals
- high diversity
- high abundance
(although still only ~3% mineralised)
Rulers of the Cambrian seas
the anomalocarids
up to 1 m long
diverse (top) predatory group
‘sponge’ = body ‘shrimp’ = grasping appendages ‘jellyfish’ = jaws
What was the Cambrian explosion?
The appearance of diverse and complex animal life, in a relatively short period of time.
Ediacaran fauna
First metazoans (animals made up of more than one type of cell) that required atmospheric oxygen for their growth.
What evidence do we have for a carnivore in the late proterozoic?
Small holes in the shells, likely some sort of sponge
What is the defining factor for the Cambrian?
When do we first see visible life?
The appearance of trilobites (one of the earliest known groups of arthropods)
We used to see visible life in the Cambrian but we now see it in the Ediacaran.
Causes of Cambrian Explosion
- Rise in Oxygen: Allowed life to get big. Size needs oxygen especially when secreting a skeleton.
Formation of collagen required >10% present atmospheric levels
Higher oxygenation favours predators - Ecological Feedback: Cambrian Arms Race. Argronomic Revolution
A metazoan arms race
Start to see organisms exploit new niches…
Burrowers:
escaping predation
or were they?
What life like a little more than half a billion years in the Cambrian?
All life was aquatic.
Most life was relatively small.
Many animals had unusual body layouts.
Characters of an arthropod?
Bilateral symmetry Segmented body Hard exoskeleton Jointed legs Many pairs of legs
Which statement best describes the “Cambrian Explosion”?
It was the time when many new animal body plans rapidly developed
Stromatolites succumb to grazing pressure and so…
cannot survive so retreat to marginal stressed habitats
