Origins of Modern Animals (The Cambrian) Flashcards
For Exam 3, May 6th (19 cards)
What is biomineralization?
When minerals produced by an organism are used to harden or stiffen existing tissues, creating bones and shells
What are the benefits of having a skeleton?
5 are listed here
Support for muscles (allows for movement), floatation devices, chemical storage, opening things like food, protection
What are some common skeletal materials?
4 most common + 2 others
Most common: Calcium Phosphate, Calcite, Aragonite, Silica
Others: Chitin (insects) and Lignin (woody trees)
What were skeletons like before biomineralization?
They were probably hydrostatic (using fluid in their bodies to move, which works well in smaller organisms because of gravity)
What is a Laggerstatte? Under what conditions does it form?
3 conditions listed
A great fossil site, which forms in areas with:
- Lots of sediments = quick burial
- Low oxygen levels = less rapid decay
- Cold environments = less rapid decay
How does levels of oxygen impact body shape and lungs?
Low oxygen levels (like those of early Earth) make it difficult for life to absorb sufficient amounts of O2 for survival, leading to:
- Flat bodies
- Wrinkles and sacs on the lungs in order to increase surface area
How does surface area and volume impact lung functioning?
They have to be similar in order for lungs to work, but volume always increases faster than surface area, so there must be wrinkles/folds
What were the Ediacaran Fossils? What does this suggest about Dickinsonia?
Early members of modern animal groups like corals, jellyfish, worms, and mollusks (clams, snails, etc.)
Dickinsonia: an early type of worm that grew by adding to its body (which was very flat b/c of low O2) similarly to modern animals
We’ve also discovered cholesteroids in them, which is only found in animals
We see a large increase in biomineralization in the Cambrian Explosion. Why?
Combination of the Arms Race Hypothesis and Magic Time Hypothesis
What is the Arms Race Hypothesis?
Things became biomineralized because of selective pressure (it was adaptive because of increasing levels of interspecies competition)
Things evolve in response to other things (competition)
What are the pros/con of the Arms Race Hypothesis?
Pros: explains the sudden appearance of shells across different lineages (for protection due to predation) and the diversity of mineralogy
Cons: there was a lack of predators in the Cambrian (why would they be evolving shells if there were no predators hunting them?)
What is the Magic Time Hypothesis?
The chemistry of the ocean at this time was at a perfect level for life to flourish
- High levels of atmospheric O2 = more collagen formation (which is what skeletons form around)
- More calcium promotes formation of shells because its toxic in high quantities (but safe to store in the shell)
How does the Magic Time Hypothesis relate to the carbon cycle?
More carbon sinks (photosynthesis, burial, absorption) = more O2 in atmosphere = more collagen
What are the pros/cons of the Magic Time Hypothesis?
Pros: explains the sudden appearance of shells without requiring the presence of predators
Cons: doesn’t explain the diversity in skeletal mineralogy
How do sea levels change and how does this affect marine life?
Melting/Forming of glaciers will cause a transgression or regression (respectively)
A transgression would = more space for marine organisms
Why were most organisms from this time bilateral?
It’s more efficient for movement and functioning of the limbs b/c it’s less costly to have a left/right axis than to have one in all directions (radial symmetry)
Explain the evolution of the eye. What were some organisms that had early eyes and what was their sight like?
We see early organisms (trilobites) with simple eyes made of calcite (evolved in a way to combat the double refraction effect of calcite)
Deeper water organisms had less eyes, but they were more complex or evolved
Starfish see only shadows
How difficult is it to evolve the ability to see?
It doesn’t take very long and it’s actually evolved many times
Summarize the order of events (starting with Hadean) thus far (i.e. end of the Cambrian)
Iron Catastrophe, Atmosphere Formation, Moon Formation, first evidence of prokaryotic and photosynthetic life, GOE, Extensive Glaciation, slowing down albedo effect, first true animal fossils, biomineralization, Ediacaran Fauna, Cambrian Explosion, evolution of eyes
