Devonian – the Age of Devonian – the Age of FishFish
DunkelosteusDunkelosteus
Life on LandLife on Land• First fossils of life on landFirst fossils of life on land
– Ordovician PeriodOrdovician Period– Possibly Middle CambrianPossibly Middle Cambrian
• Why did Earth go so long without Why did Earth go so long without life on land?life on land?
• What prevented life from inhabiting What prevented life from inhabiting the land?the land?
Barriers to life on landBarriers to life on land• DehydrationDehydration• Osmoregulation: fresh vs. salt waterOsmoregulation: fresh vs. salt water• Reproductive dispersalReproductive dispersal• SupportSupport• Food supplyFood supply• Temperature extremesTemperature extremes• Exposure to UV and other radiationExposure to UV and other radiation
Life on LandLife on Land• What do you suppose the earliest What do you suppose the earliest
colonizers were like?colonizers were like?• Where would they have lived?Where would they have lived?• What advantages might there be to What advantages might there be to
living on the land?living on the land?
The Fossil Record:The Fossil Record:• Limited record of marine Limited record of marine
macrophytes – macrophytes – environmental environmental requirements vs. requirements vs. preservationpreservation
• Ordovician (Middle Ordovician (Middle Cambrian?) - spores in Cambrian?) - spores in marine sedimentary rocksmarine sedimentary rocks
• Spores indicate primitive, Spores indicate primitive, moss-like (non-vascular) moss-like (non-vascular) plantsplants
First Vascular Land First Vascular Land PlantsPlants
• Conducting tissueConducting tissue• StomatesStomates• No true roots – simple “hold fasts”No true roots – simple “hold fasts”• Appeared in Late Silurian to Early Appeared in Late Silurian to Early
DevonianDevonian
CooksoniaCooksonia
RhyniaRhynia
AglaophytonAglaophyton
AsteroxylonAsteroxylon
ArchaeopterisArchaeopteris – Middle – Middle DevonianDevonian
Archaeopteris/CallixylonArchaeopteris/Callixylon
Callixylon/ArchaeopterisCallixylon/Archaeopteris• The “Gilboa The “Gilboa
Forest”Forest”• First forest – First forest –
Gilboa, NYGilboa, NY• A new ecosystemA new ecosystem• New conditions – New conditions –
adaptations to adaptations to shadeshade
ZosterophyllZosterophyll – Middle – Middle DevonianDevonian
What about Animal Life?What about Animal Life?• Rhyniaphytes show scars from Rhyniaphytes show scars from
arthropod (insect) predationarthropod (insect) predation• Why would arthropods be first to Why would arthropods be first to
colonize land?colonize land?• What about vertebrates?What about vertebrates?
EusthenopteronEusthenopteron
EusthenopteronEusthenopteron – a – a “missing link”“missing link”
AcanthostegaAcanthostega – an early – an early amphibianamphibian
LatimeriaLatimeria – a modern – a modern crossopterygiancrossopterygian
IchthyostegaIchthyostega – First – First AmphibianAmphibian(M. Dev.)(M. Dev.)
IchthyostegaIchthyostega
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