Cambrian Explosion

Question 1

When did the cambrian explosion happen?

Answer 1

right after the ediacarans. fuse for evolutionary life.

Fossils suggest that there were nothing before trilobites but thats wrong!

Question 2

What suddenly appeared in the early cambrian?

Answer 2

Biomineralized shells and skeletons, the majority of pHyla were emerging rapidly. and EVERY phyla that exists today emerged here.

Question 3

What is evidence of earlier biomineralization in ediacaran?

Answer 3

Sponge spicules! Fuse together to form scaffolding in sponges.
Biomolecular evidence from Oman - 635Ma.

Cloudina: found with Ediacarans
- primitive snidarian organism/tube dwelling??nobody is sure. Maybe its a worm that secretes calcium carbonate tubes.

Question 4

Where is the base of the cambrain and phanerozoic period?

Answer 4

Newfoundland, Fortune head. Identified by a trace fossil.
- bioturbation. Previous sediments were just horizonal laminates, with some stromatolites. now you have interaction, marked by a trace fossil called TREPTICHNUS PEDUM. - unknown metazoan. 542ma

Question 5

What is the 1st phase of the cambrian explosion?

Answer 5

Conodontomorphs.
Not conodonts!!!!
Found at top of precambrain, latest neoproterozoic. Simple vase shaped, maybe with teeth. pretty weird.

Question 6

What is the 2nd phase of cambrian explosion?

Answer 6

Small shelly fauna (SFF)
Diversify at Tommotian stage of cambrain, some seen in late neoproterozoic.

1. Skeleton of small creatures
2. mineralized parts of larger creatures

• cloudina, anabarites, anabarella, camenella, aldenella, sponge spicule, formitchella, lapworthwella

Most only a few mm long, and extinct after 3-4 million years.

Question 7

What are camenella?

Answer 7

Sclerites that were part of an articulated armour of plates. Maybe an armoured worm?

Question 8

What is the 3rd phase of the cambrian explosion?

Answer 8

follows tommotian.
BIG stuff here (trilobites)
where modern phyla evolve.

Question 9

What drove diversification?

Answer 9

1. Increased size
   - possibility of limbs and muscles on those limbs
   - interact with environment more effectively
2. UV and desiccation protection.
   - exploiting new shallower environments. since ozone is increasing, calcium carbonate hats can also allow for difficult environment habitation.
3. Predation
   - found holes in cloudina, possible teeth in SFF
   - this would drive evolution and natural selection.
4. Eyes. Improved visual systems to drive evolution.

Question 10

Describe visual pigments and their role in evolution of eyes.

Answer 10

Shared by many animals, early metazoans would just be able to detect light “eye spots” i.e. Euglena, protist.

When this was “depressed” into a cup, it improves sense of brightness and light direction. i.e. flatworms.

Deepen the pit and have a small opening allows for fuzzy imaging i.e Nautilus

Cover hole with a lense (transparent cells) to prevent material getting into eye and refract light towards retina. Makes lens and real image.

Bible lovers hate this evolutionary idea.

Question 11

What is Euglena?

Answer 11

A protist that had an eye spot.

Question 12

Who had the 1st eye system? describe it. main types?

Answer 12

Trilobites.
Compound (multiple) lenses of calcite, very sensitive to sudden movement.
Couldn’t cope with bright sunlight - sunshade/lip on eyes of trilobites found in shallow water. adaptations!!

Two main types.

1. Holochronal: lots of lenses, small, one corneal layer that directly contacts adjacent ones, no sclera in between.
2. Schizochroal: fewer lenses, larger lenses, individual cornea separated by sclera and a deep cornal membrane.

Variations in eye styles
i. Stalked eyes, Eyeless, Holochral large eyes. Weird things. Some lost their eyes cause they are burrowing trilobites.

Question 13

Who is Andrew Parker?

Answer 13

Thought camb explosion was solely driven by vision and eyes to improve hunting. Drive prey to develop armor etc.
THis doesn’t make sense cause animals hunt in many ways. it was likely a combo of factors.

Question 14

What are the 4 theories of explosion ?

Answer 14

a: darwin’s theory that it started in cambrian
b: stephen gould’s theory that there was more diversification in cambrian and then its been pruned.
c: very long fuse starting around 900MA
d: roots in precambrain but started a bit earlier.
We don’t know which one it is, just that A is wrong forsure.

Question 15

What happens by middle cambrian?

Answer 15

We have all major phyla and never get any more!

Question 16

What are brachiopoda?

Answer 16

lamp shells that were very important in paleozoic. still find them today!

Question 17

What are mollusca?

Answer 17

Diverse group of gastropods, bivalves and cephalopods.

Question 18

What are arthropoda?

Answer 18

diverse metazoan group that includes trilobites, crustaceans and INSECTS.

Question 19

What are echinodermata?

Answer 19

Starfish, crinoids etc.

Question 20

What are hemichordata?

Answer 20

Acorn worms, pterobranchs and graptolites!

Question 21

What are chordates?

Answer 21

the vertebrates!!

Question 22

What species are from ediacaran?

Answer 22

only cnideria and porifera!
Everything else except chordates are from early cambrain!!
all body plans will be from here

Question 23

What modes of life were in the early cambrian?

Answer 23

Fauna on the sea floor, free moving, suspension feeders (brachiopods, eocrinoids - relatives of sea urchins)
Stromatolites were more restricted, mostly in intertidal zone where others couldn’t live.

Question 24

What were the Archaeocyathids?

Answer 24

They took over the role of reef producers, types of sponge that pump water through bodies and filter useful material. Extinct by end of cambrian.

Question 25

How many of our ocean’s organisms are soft bodied?

Answer 25

60%

We were totally skewed in our perception before we had “windows” into the cambrian world.

Question 26

What is the Burgess SHale and Burgess shale type deposits? Where are they mostly found in North America?

Answer 26

Burgess shale: middle cambrain deposit in canadian rockies where they found soft bodied fossils.
Found others…

Chenjiang fauna in Yunnan province, more faunas in the ordovician.
(Se morocco fauna, Sirius Passet fauna, Wheeler shale fauna.

They were all found on the ancestral paleoequator!

Question 27

Why are lagershtattten so much more rare after middle cambrian?

Answer 27

Deeper and more extensive burrowing led to not as good preservation.
Stromatolites were sticking things together to preserve them but they’re becoming more rare.

Taphonomic window closing due to advancement of the biosphere.

Question 28

What are some “oddballs” of the cambrian?

Answer 28

Echinoderms.
- Asteroidea, Crinoidea, Holoturoidea, ophinuroidea, echinoidea.

• Water vascular system that allow movement due to pumping,
• 5 fold symmetry
• calcium carbonate plate skeleton.

Helicoplacus has these things but not 5 fold symettry, its like an ecinoderm but odd.
Homalozoa: just weird! no idea what it did.

Question 29

What are HOX genes?

Answer 29

Maybe why we don’t see the oddness in our world anymore. They are CONTROL GENES that tell the genome what to do.
- more recently, the more control genes you have. The rules become more strict. In cambrian it was more flexible, now all phyla are defined and obey all the rules.