Origin of Animals / Cambrian Explosion

Question 1

What was the first animal?

Answer 1

Phylum porifera: the sponges

Question 2

What is an animal?

Answer 2

• multicullular
• aerobic
• hetrotroph
• ingests then digests
• mobile
• diplontic life cycle
• specialized tissues from different layers during the early stages of development

Question 3

Describe Edicaran lifeforms

Answer 3

Sessile (slow moving) meanderers
No eyes or complex sensory system
No shells/hard surfaces
Eat microbial mats off the sea flor

Question 4

Name 6 big developments from the Cambrian explosion

Answer 4

1. Burrowers/swimmers: life goes 3D
2. Active predation
3. Shells (appear at Ediacaran and diversify in Cambrian), exoskeletons, spines
4. Bilateral symmetry/body segmentation
5. Complex eyes and other complex sensory systems
6. Big time diversification

Question 5

What three general things sparked the Cambrian Explosion?

Answer 5

1. Change in environmental conditions
2. Bilaterian Developmental Toolkit
3. Changes in ecological interactions

Question 6

Change in environmental conditions =

Answer 6

• Increased continental erosion (higher levels of minerals: calcium for shells; atmospheric oxygen)
• Increased oxygen leads to higher levels of activity

Question 7

Evolution of the bilaterian developmental toolkit =

Answer 7

• Diversification of bilateral symmetry
• Homeobox gene duplications (Hox genes)
• Independent evolution (in different animal groups) of nervous systems, sensory systems, brains, circulatory systems, respiratory systems

Question 8

What are the two groups of bilateral animals?

Answer 8

Deuterostomes and protostomes

Question 9

What are protostomes?

What are deuterostomes?

Answer 9

Blastopore becomes mouth.

Blastopore becomes anus

Question 10

Give an example of bilateral symmetry, radial symmetry, and no symmetry.

Answer 10

• Beetle
• Coral polyp
• Sponge

Question 11

Hox genes are present…

Answer 11

In all bilateral animals

Question 12

Changes in ecological interactions =

Answer 12

• increased O2 = active predation and grazing
• opened up microbial mat to gain access to ocean floor sediment = burrowing
• evolutionary arms race between predator and prey
• coevolution = greater diversity and ecological complexity

Question 13

What is adaptive radiation?

Answer 13

Rapid production of many descendant species from a single lineage

Question 14

What are the three hallmarks of an adaptive radiation?

Answer 14

• Monophyletic group
• Speciate rapidly
• Diversified ecologically into many niches