1: The Cambrian Explosion

Question 1

Define Metazoan

Answer 1

Multicellular organism

Question 2

What characteristics do metazoans share?

Answer 2

Multicellular body formed from different kinds of cells
The ability to manufacture the protein collagen
A reproductive cell with gametes produced by meiosis
A nervous system composed of neurons

Question 3

Recent advantages in several fields have been important in addressing the problem of the origin of metazoans such as

Answer 3

• New fossil finds
• Phylogenetic analysis of anatomical and molecular data
• Molecular clock studies
• Molecular genetics of animal development

Question 4

Describe Ediacaran organisms

Answer 4

Have no mouth, gut or anus so they either fed through:
- Photosynthetic algae
- They took in their substance through the body wall
- Chemosymbiosis

Question 5

Define a Triploblastic animal

Answer 5

Ones with three germ layers allowing organs to develop

Question 6

Describe the early Cambrian

Answer 6

• Some shelly fossils are probably disarticulated elements of skeletal covering that had yet to evolve into a large discrete shell covering the entire organism
• They are almost certainly an adaptation against predation and probably represent either an extinct phylum close to the mollusca or some form of annelid (creature with no backbone)

Question 7

Describe the Middle Cambrian

Answer 7

During the middle Cambrian fossils appear, at the same time and worldwide of organisms with preservable hard parts. Interestingly these include essentially representatives of all modern phyla with hard parts
Why have no new phyla appeared since the cambrian explosion?
How do we explain the sudden dramatic increase in diversity and disparity and then its demise?
The cambrian explosion represents a true evolutionary burst to large size and greatly increased anatomical vairety as well as the appearance of fossilizable parts has fossils can only develop once they have formed armour

Question 8

Describe the environmental causes of Cambrian explosion

Answer 8

• Long lived ‘super continent’ broke apart
• Two extensive glaciation
• Boulder clay is bound by carbonates and above by cap carbonates
• Carbonates have exceptionally high C-isotope values reducing atmospheric C02 and leading to the glaciations
• Banded iron formations occurring and iron accumulates in the oceans
• Finally, short isotope excursion in the
  latest Precambrian coinciding with the extinction of skeletal fossils from microbial reefs
• Atmospheric 02 rises dramatically

Question 9

Describe the ecology during the late precambrian

Answer 9

Late Precambrian: Ediacaran animals inhabit the sea floor and are unprotected but have no predators

Question 10

Describe the ecology during the early-middle Cambrian

Answer 10

Early-middle cambrian: Triploblastic predators with teeth evolve and most ediacara organisms become extinct. Other multicellular organisms with armour evolve

Question 11

Describe the ecology during the late cambrian

Answer 11

Late cambrian: Predators become more efficient and multicellular animals evolve better armour and exploit more burrowing niches