The Cambrian Explosion

Question 1

What is Shcinderhannes bartelsi?

Answer 1

Great appendage arthropod from the Devonian and Cambrian

Question 2

Who notes the absence of a common ancestor for trilobites?

Answer 2

Darwin - shortly after we found it was the Cambrian

Question 3

Where is the Burgess Shale?

Answer 3

Canadian Rockies

Question 4

Who discovered the Burgess Shale?

Answer 4

Charles Doolittle Walcott

Question 5

What recognisable arthropod was found due to its jointed appendages?

Answer 5

Marella splendens

Question 6

What was early Cambrian, Burgess shale of Chengjiang?

Answer 6

Chengjiang

Question 7

Were there any new phyla after the Cambrian?

Answer 7

No

Question 8

Name an animal from the Edicaran that looks like a modern ‘sea pen’

Answer 8

Charnia wardi

Question 9

What was weird about fossils from Edicaran?

Answer 9

There were three different environments but very similar morphology, minimal variation. Same adaptations to different environments. Not active looking.

Question 10

How did we find out about the increase in oxygen from the Edicaran to Cambrian?

Answer 10

Chromium isotopes. Oxidised state is heavily enriched with heavy isotope. Heavy isotope soluble in water. So lots of oxygen, results in lots of oxidised chromium, soluble, flows into oceans, deposited in sedimentary rock.

Question 11

Why would more oxygen indicate a rise in disparity?

Answer 11

Oxygen is needed for larger animals, not physically possible to have big bodies with little oxygen

Question 12

What elements increased considerably in the oceans and why were they linked to increased animals?

Answer 12

Calcium, used for skeleton formation, phosphorous, a nutrient.

Question 13

Why did calcium and phosphorus levels rise?

Answer 13

Rising sea levels, shallow continental shelves, calcium and phosphorus washed into the sea

Question 14

What did rising sea levels mean?

Answer 14

Larger area for potential habitat, remember all animals were marine at this point

Question 15

Why is there an absence in the fossil record in the Edicaran?

Answer 15

Nature of body plans and lack of skeletons

Question 16

What animal was found to form burrows in the Cambrian and how was it found to do this?

Answer 16

Priapulida, modern day priapulids found in deep seas of Sweden, similar movement to fossils of ancient priapulida, forward backward motion.

Question 17

What was so special about Priapulida?

Answer 17

Burrowing = oxygen in marine sediment, allowing for other burrowing animals. Animals used to feed on algal mats but priapulid was first predator, changing ecology massively

Question 18

What might carbon isotope increase around the time of the Cambrian indicate?

Answer 18

Saw carbon isotope increase when mass extinction event at the end fo the cretaceous that wiped out the dinosaurs. Perhaps event occurred that wiped out all Edicaran animals, make way for Cambrian ones to occur? Or perhaps the increase in disparity in the Cambrian is what caused the change in isotopes. Can’t be sure of the order of events

Question 19

What is hypothesised to have happened to Edicarans?

Answer 19

Either wiped out, or ancient ancestors, some fossils have been likened to starfish and echinoderms.

Question 20

What are the environmental factors for the Cambrian explosion?

Answer 20

Increased oxygen levels
Increased sea level
Increased the habitat and minerals
less snowball earths and extreme glacial events.
Fast continental movement leading to methane burps and increasing temperatures.

Question 21

What are the developmental factors for the Cambrian explosion?

Answer 21

All of genes to make animals already exist in animals, thought would need new set of genes but just reuse.
At a certain complexity hard to change components because by changing a role of a gene you might change a vital function (developmental lock), might explain why we don’t get anything new.
Evolution of through-gut (mouth and anus) key to getting bigger animals. Body cavity evolution.
Allow to connect muscles within body cavity allowing for movement within the body and external force on the environment, changing the environment.

Question 22

What are the ecological factors for the Cambrian explosion?

Answer 22

Churning of marine sediment, origin of predation arms race.
Once you evolve certain number of body plans you saturate certain ecological niches, making it hard for new animals to invade that space (why we get no new animals)

Question 23

What are the theoretical factors for the Cambrian explosion?

Answer 23

Roughening of the fitness landscape.
Developmental system limits what can be produced morphologically, only having one selection pressure (food) very few optimal body plans to achieve that, once you get more selection pressures like weather and predators there becomes more solutions.