Skeletons in the Rock: After the Explosion

Question 1

Most of the modern animal phloem started after the Cambrian explosion (particularly invertebrates)
Why?

Answer 1

This is due to established ocean/hydrophere system, as well as higher oxygen level, formation of ozone and increasing nutrient levels
Before this in the Edicaran period, most organisms were simply and unicelluar

Question 2

When did the Cambrian explosion occur

Answer 2

541Mya during the Cambrian periods

Question 3

What is the significane for the Cambrian Explosion and life on Earth now?

Answer 3

• It resulted in the divergence of most modern metazoan phyla and was accompanied by major diversification of other organisms
• Over the proceeding 70-80My, the rate of diversification increased, and the variety of life began to resemble that of today

Question 4

What is a species

Answer 4

Two organisms which have similar characteristics and can produce fertile offspring

Question 5

Name some examples of appearances of animal phyla which occured after the Cambrian explosion

Answer 5

• Anthropods with hard exoskeletons
• Brachiopods
• Bryozoans
• Crustaceans
• Echinoderms (e.g. sea urchins)
• Molluscs (e.g. bivalves + gastropods)

Question 6

Why did the Cambrian explosion happen

Answer 6

• A big increase in free oxygen in the atmopshere and oceans
• The development of an ozone layer to protect the planet’s surface from harmful extraterrestrial ultraviolet radiation
• A tipping point in biological evolution e.g. lots of new, benefical innovations/adaptations
• An evolutionary ‘army race’ - innovations for predators led to denfensive adaotations

Question 7

What are Marine Metazoans

Answer 7

Marine organism which occured in ‘middle life’

Question 8

What does Palaeozoic mean

Answer 8

Old life

Question 9

What does Mesozoic mean

Answer 9

Modern life

Question 10

What is the significance of Cambrian Fauna

Answer 10

All Cambrain Fauna all now cease to exist

Question 11

What are Vascular land plants

Answer 11

They are advanced land plants
Not including organisms like algae

Question 12

Explain the shape of the graph showing the number of Marine Families after the Cambrian Explosion

Answer 12

• There is a sharp rise at the end of the Cambrian, indicating high levels of diversification likely due to many empty niches
• The plateo after that indicates Ecospace becomes full, reached capacity
• The great dying at the end of the Paleozoic
• Recover and radiation heading into the Mesozoic period with lots of current modern biota present

Question 13

How during the Paleozoic dud the oceanic marine families reach capacity of 450 families but during the Mesozoic the number of oceanic mesozoic species exceeding 780

Answer 13

Prior to the Jurassic, there was a marine connecting the oceans across America (gulf of Mexico)
This allowed different species to mix, which could trigger evolution
However the reason for this disparity is not quite solved

Question 14

What is a Paleobiology Database

Answer 14

A complication of data on marine metazoans minus tetrapods from fossil collections that represent small geographical areas and narrow time ranges
Data is binned into 49 uniform time intervals using 44,446 collections
This has allowed the previous graph to be formed by Sepkoski

Question 15

What is the issue with Sepkoski graph

Answer 15

Pull of the recent - an example of bias - modern things are very self evident
Genera are pulled forward to the recent or only to their last fossil occurences
However this is the best science can manage

Question 16

What is the issue with some fossil records

Answer 16

• Rock environments and which ones are exposed
• Inconsistent sampling effort and bias on ‘times’ analysed
• Some taxa fossilise better, e.g. bigger and robust
• Never can find the first and last individual of a species
• Pull of the recent
• Impossible to correct for these biases - even if correction were possible, we have no idea what we are missing, and thus no idea what a ‘corrected’ record looks like