9. Skeletons in the Rocks

Question 1

When did the Cambrian explosion occur?

Answer 1

Approx 541 Ma

Question 2

Across how many years did the Cambrian explosion take place?

Answer 2

13-25My

Question 3

What were organisms like before the Cambrian explosion?

Answer 3

Mostly simple and unicellular

Question 4

What major feature appeared significantly for the first time in the Cambrian explosion? How does this compare to previous Ediacaran biota?

Answer 4

Animals with hard shells - in comparison to soft bodied Ediacaran biota.

Question 5

What are 6 examples of animal phyla that first appeared during the Cambrian explosion?

Answer 5

Arthropods, brachiopods, Bryozoans, Crustaceans, Echinoderms, Molluscs

Question 6

What environmental factors are speculated to have caused the Cambrian explosion?

Answer 6

Big increase in free oxygen, the development of the ozone layer protected life from harmful UV

Question 7

What ‘biological tipping point’ accelerated evolution and diversification?

Answer 7

Increasingly advantaged predators caused an increase in evolution of their prey to compete.

Question 8

Are Cambrian fauna still widespread?

Answer 8

No, mostly extinct

Question 9

Who was John ‘Jack’ Sepkoski?

Answer 9

A palaeontologist who studied the fossil record and diversity of Life, he created a famous graph of marine lifeforms over time.

Question 10

How are the four defined sections of the Sepkoski graph explained?

Answer 10

Initial curve (Cambrian and Ordovician): rush to fill ecospace
Flat line (Silurian, Devonian, Carboniferous, Permian): ecospace full, little excess nutrient
Permian Extinction
Recovery during Triassic, Jurassic, Cretaceous, and Cenozoic

Question 11

What is significant about the number of marine families stabilising at around 450 in the Paleozoic?

Answer 11

We’re now at 780, a vastly higher number

Question 12

What are some suggested reasons that marine life has higher diversity now than in the Palaeozoic?

Answer 12

Changing of conditions, there is new marine connection now due to newly connected seas

Question 13

What skews Sepkoski’s data that could affect perceived diversity in modern times?

Answer 13

‘Pull of the recent’
- Modern period looks diverse because it’s easy to measure things that are still alive, and recent fossils are more likely to still be intact.

Question 14

What did Alroy do to reduce sampling bias?

Answer 14

Limited references per period (periods of 11My) since some are more investigated.

Question 15

Why are some species more likely to be represented in the fossil record? (fossil record bias)

Answer 15

Some taxa fossilise better (e.g. more robust ones)
Some taxa survive dissolution better
Certain periods are studied more
Certain regions are studied more
Some environments don’t form rock, or rock formation is less common

Question 16

Why is it hard to gauge species duration from fossils?

Answer 16

Never find the first or last individual of a species.

Question 17

What are some pros of Alroy’s data over Sepkoski’s?

Answer 17

• Digital data, can be manipulated more easily and individual genus’s can be studied
• Less sampling bias

Question 18

What database did Alroy use?

Answer 18

Palaeobiology database

Question 19

What types of animal were Alroy and Sepkoski studying? What did Alroy remove from this?

Answer 19

Marine metazoans (Alroy removed tetrapods too)

Question 20

Why is it harder to study short-lived species?

Answer 20

Short lived species are less likely to be preserved