Devonian

Silurian and Devonian:

Silurian and Devonian:
– High sea levels
– Shallow, epi-continental seas
– Diverse marine life
– Existing species radiated, new species evolved, especially reef ecosystems
– Large jawed fishes
– On land: plants emerge, thrive in Devonian, as do insects, other vertebrates

Renewal of Life
• Coral-strome reefs flourished
– Greatest size in Devonian
• Ecologic succession
– Tabluates and rugose corals colonized seafloor
– Other animals populated reef

Swimming animals originated

Swimming animals originated
Ammonoids:

– coiled cephalopod mollusk
-Evolved from straight nautiloids in Early Devonian
-Widespread
-Guide fossil

Jaw evolution

Jaw evolution
– Devonian
– Bars supported gills in primitive fishes
– Modified gill bars led to jaws

Fishes

Fishes

• Placoderms
– Very large fishes
– Predators
– Dominated freshwater environments

Late Devonian, fishes diversified in the seas

Late Devonian, fishes diversified in the seas

– Dunkleosteus
• 7 m long armored fish
• Unarmored tail
• Bony plate around eye, bony teeth

Cladoselache
– Small shark
– Often found with Dunkleosteus

Ray-finned fishes

Ray-finned fishes
– Devonian
– Bones radiate from fins to support fish
– Cheirolepsis; related to
trout, tuna, bass, herring

Sharks

Sharks
– Mid-Devonian appearance
– Primitive and small
• 1 m

Lobe-finned fishes

Lobe-finned fishes
-paired fins, attached by single shaft
-gave rise to ALL TERRESTRIAL VERTEBRATES.

• Baragwanathia
– Non-marine
– Large (1 m height)

Plants

Spores: wider range for reproduction
Ferns
– Early Devonian
• Definitely land plants
• Possess upright stalks

Lycopods
-Club mosses:

-small, required water for reproduction

Early and Middle Devonian evolution

Early and Middle Devonian evolution

Early Devonian spore plants
restricted to marshes
– Required water for reproduction
– Development of the seed freed
plants from water
-allowed higher rates of photosynthesis

-seedless Archaeopteris formed first wide-spread forests

 

Late Devonian Plants

Late Devonian Plants
-Large trees evolved as leaf size increased
-allowed higher rates of photosynthesis;

-seedless Archaeopteris formed first widespread forests

Seed bearing plants

Seed bearing plants
-Seeds allowed plants to move away from constantly wet environments, colonize dry habitats

-Land plants with roots stabilized soil, prevented erosion; major change in pre- vs. post-Devonian
time period

Early Terrestrial Animals

Early Terrestrial Animals
-Some fragmentary, simple terrestrial animal fossils from Late Silurian
-Once land plants expanded, more invertebrate animal fossils found in early Devonian sediments:
-Millipedes, flightless insects that ate plant debris
-Scorpions, centipedes, spiders - carnivores
-Interestingly, no herbivores, like leaf eaters; dead plant material supported early terrestrial food webs

Vertebrates:

Vertebrates:

-four-legged vertebrates most closely related to fish like frogs, toads, salamanders were first out of the oceans onto land
-Amphibians lay eggs in water, spend early part of life there, then metamorphose into air-breathing land dwellers
-Paleozoic amphibians were a lot bigger than those present today

-Lobe-finned lung fishes probably used them when lakes or streams dried up; allowed animals to move
onto land

Other traits similar between amphibians and lobe-
finned fishes:

Other traits similar between amphibians and lobe-
finned fishes:
-complex tooth structures

Animals Invade Land

Animals Invade Land
• Late Devonian meandering
stream deposits; intermediate
between lobe finned fish and
amphibians in body form

Tiktaalik

Tiktaalik

Fish-like features:
-fins
-scales
-lower jaw
Amphibian-like features:
-toe-bones in front fins
-flexible wrist bones
-crocodile-like skull, nostrils on upper surface

Amphibians

Amphibians
– Latest Devonian
– Return to water to lay eggs
– Flexible neck
• Ichthyostega
• Intermediate between
amphibians and lobe finned fishes
• Had toes

-came after Tiktaalik

Euramerica:

Euramerica: Laurentia + Baltica + Avalonia; connected landmasses that now make British Isles

Euramerica: lots of shallow, carbonate reef formation

Early Devonian Paleogeography

Early Devonian Paleogeography
Euramerica= Laurentia, Baltica, Avalonia
High sea level

–melted Ordovician glaciers

-large land mass at equator with no glaciers changes albedo
-Lots of shallow shelf at
low latitudes —> carbonate
deposition, reef habitat

Euramerica:

Euramerica:
Warm, dry climate
-Abundant reefs
-Evaporites
Paraná Basin (S. Amer.):

-Cool water fauna

–burrowing bivalves

Devonian Western Euramerica

Devonian Western Euramerica
• Abundant moisture around equator
– Coal
• Dry in rain shadow
– Evaporites

Antler Orogeny

Antler Orogeny
– First orogeny for western Laurentia/Euamerica
– Island arc accreted
• Ophiolites

Western Euramerica
– Klamath Mountains
– Sierra Nevada Mountains
– Deep-sea deps 100 miles inland

-1st phase of west coast
mountain building!

Late Devonian Glaciation: Tillites over southern Gondwanaland, Why?

Evolution of land plants
-pulled CO2 out of atmosphere, stored as organic matter
-increased rates of silicate weathering, also lowers atmospheric CO2
-lead to a mass extinction

Late Devonian Glaciation
• 1st Extinction event:

Late Devonian Glaciation
• 1st Extinction event:
-Atrypid brachiopods
-Reefs, and reef builders, including siliceous sponges
-Ammonites
Survivors:
-bivalves, gastropods, bryozoans

àTransformed tropical marine ecosystems, cold ones survived.

Terrestrial plant extinctions, too

Late Devonian Glaciation geochemistry:

Late Devonian Glaciation geochemistry:

Brachiopod shells record elevated d 13C,d 18O values
• Silica secreting sponges increase, reefs decreased

Late Devonian Glaciation
• 2nd Extinction event at very end of Devonian:

Late Devonian Glaciation
• 2nd Extinction event at very end of Devonian:
-placoderm fishes; none survive into Carboniferous
-planktonic acritarches never recovered diversity.

àDevastated base (acritarch and coral-Strome reefs) and top (placoderm fishes) of food web, re-organized marine ecosystems

Massive tillites deposited in present day Pennsylvania, 30°S; Gondwanaland glaciers extended towards equator.