Devonian

1
Devonian the Age of Fish
2
Dunkelosteus
3
Life on Land

• First fossils of life on land
• Ordovician Period
• Possibly Middle Cambrian
• Why did Earth go so long without life on land?
• What prevented life from inhabiting the land?

4
Barriers to life on land

• Dehydration
• Osmoregulation fresh vs. salt water
• Reproductive dispersal
• Support
• Food supply
• Temperature extremes
• Exposure to UV and other radiation

5
Life on Land

• What do you suppose the earliest colonizers were
  like?
• Where would they have lived?
• What advantages might there be to living on the
  land?

6
The Fossil Record

• Limited record of marine macrophytes
  environmental requirements vs. preservation
• Ordovician (Middle Cambrian?) - spores in marine
  sedimentary rocks
• Spores indicate primitive, moss-like
  (non-vascular) plants

7
First Vascular Land Plants

• Conducting tissue
• Stomates
• No true roots simple hold fasts
• Appeared in Late Silurian to Early Devonian

8
Cooksonia
9
Rhynia
10
Aglaophyton
11
Asteroxylon
12
Archaeopteris Middle Devonian
13
Archaeopteris/Callixylon
14
Callixylon/Archaeopteris

• The Gilboa Forest
• First forest Gilboa, NY
• A new ecosystem
• New conditions adaptations to shade

15
Zosterophyll Middle Devonian
16
What about Animal Life?

• Rhyniaphytes show scars from arthropod (insect)
  predation
• Why would arthropods be first to colonize land?
• What about vertebrates?

17
Eusthenopteron
18
Eusthenopteron a missing link
19
Acanthostega an early amphibian
20
Latimeria a modern crossopterygian
21
Ichthyostega First Amphibian(M. Dev.)
22
Ichthyostega