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