Transcript LECTURE 4: Paleozoic Era: Silrian/Devonian

LECTURE 5: Paleozoic Era
Silurian/Devonian Periods
(439 mya- 360 mya)
What Index Fossil appears at the
Beginning of the Silurian?
• Parakidograptus
acuminatus
– Extinct group:
graptolite
(hemichordate)
What Significant Events Happened
during the Silurian and Devonian?
• Life emerged from the water and colonized
the land.
– Plants (green algae evolved into bryophytes, then
tracheophytes) and animals (insects)
KEY DEVELOPMENTS:
– The development of vascular plants, pollen and
seeds
• provided plants with a way to reproduce and survive on dry
land, creating new habitats
– The development of jaws
• allowed fishes and other emerging vertebrates to catch larger
prey
– The development of tetrapods—
• limbed animals—would pave the way for animals that could
walk on land
Why did Plants Move onto Land?
• The ozone layer shielded life like water once
did
– Gave protection from the sun’s harmful radiation.
Only water had provided this protection before
• Soils had formed that could nourish plant life
– Bacteria, algae, and fungi had gained an early
foothold on land, secreting organic acids that
broke rock down into its mineral elements.
Nutrient-rich soils formed as these organisms
died and their decaying matter combined with the
minerals.
– The next Plants to evolve were vascular plants
What Adaptations are Required
for Land Plants?
• Stand Upright (no support form water)
• Tolerate UV radiation
• Tolerate Climate Changes
• Be able to acquire nutrients from substrate
other than water
• Produce gametes (seeds) that can move in
the air
How did Plants Evolve?
1. Green Algae
2. Bryophytes (430 mya)
•
•
•
Non- vascular
Moist areas
Mosses/liverworts (spores)
3. Seedless Tracheophytes (420 mya)
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•
Vascular
Ferns, horsetails
4. Seed Producing Tracheophytes (365
mya)(Gymnosperms)
First land plants
(Bryophytes)likely similar to
extant leafy liverworts…….
What is the Oldest Fossil Plants?
• Cooksonia – 428 mya
– Bryophyte
– Small, few cm long
– No leaves, roots
horizontal stems
with hairs
connecting to soil
What was a Trimerophyte?
• Trimerophyte (seedless vascular plant)
– stems with branches
Pertica quadrifaria
• these leafless plants are early
relatives of every seed-bearing
plant, fern, and horsetail living
today
• By the end of the Devonian:
– Extensive forests (club moss and horse tail
ancestors) with tall trees (Seedless TracheophytesLycophytes)
– These plants later were out competed by seed
plants and nearly all have gone extinct
Why did Jaws Evolve?
• The vertebrate jaw can be traced back to 440 mya
• Most jawless fishes went extinct,but jawed fishes
became the ancestors for most modern fishes today.
• Jaws evolved from gill arches (Gnathostomes- jawed
Fish)
– From Jawless fish (Agnathas)
• Helped fish catch food
– Jaws allow mouths to open wide and catch larger prey
– Jaws with teeth can bite, crush, and chew.
• Protected by bony, overlapping plates, Placoderms were among the
first fishes with jaws
Placoderm fish armored head
Dunkleosteus terrelli
Devonian (417-354 million years ago)
Cleveland, Ohio
Stretching up to twenty feet long and sporting powerful jaws (no teeth)
equipped with tooth-like plates, Dunkleosteus was one of the world’s
first large vertebrate predators.
FISH GROUP
KEY FEATURE
Jawless Fish (agnathas)
500 mya
- no jaws
- no paired fins
- gave rise to placoderms,
cartilaginous and bony fish
Placoderms – First Jawed Fish
(Gnathostome)
439 mya
-Jaws without teeth
- Armored fish
-Paired fins
Cartilaginous (Chondrichthyes)
395 mya
- cartilage skeletons
- no swim bladder
- no lungs
- internal fertilization
Bony (Osteichthyes)
Actinopterygians (ray-finned)
Sarcopterygians (lobe-finned)
- gills
- lungs
- swim bladder
- some developed fleshy lobe fins
(gave rise to amphibians)
When did Tetrapods Evolve?
• Fish were the first animals to develop “feet” about
370 mya
– Sarcopterygian fishes had muscular lobes at the bases of their
paired fins. Within these lobes were large bones, one of which
connected the rest of the fin bones to the body, like toes on a
foot
– Their fins were made for walking.
Over time, some Sarcopterygian fishes may have begun using
their muscular, lobed fins to "walk" in shallow, swampy waters,
pushing their way through dense plant growth
– Tetrapods branched out to include many familiar animals.
From one type of Sarcopterygian fish evolved the first tetrapods:
• vertebrates with four paired limbs and digits (fingers and toes)
What is a Coelacanth?
• "living fossil" – only
lobe-finned fish in
existence
• Evolved about 360
mya
• paired lobe fins that
extend away from its
body like legs and
move in an alternating
pattern, like a trotting
horse
What is the Evidence for
Tetrapod Evolution?
• Homologous Structures
– The front fins of certain sarcopterygian
fishes and the front limbs of tetrapods
share the same bones: humerus,
ulna, and radius.
– The hind fins of certain sarcopterygian
fishes and the hind limbs of tetrapods
share the same bones: femur, tibia,
and fibula.
• Sarcopterygian fins are paddle-like,
while tetrapod limbs have digits
(fingers and toes) that grip the ground
Eusthenopteron: "Fish with Legs"
(Transition to tetrapod)
Panderichthys (“Fish with Fingers”)
Tiktaalik- 375 mya
• Extinct Sarcopterygian
• They may have begun using their muscular,
lobed fins to "walk" in shallow, swampy waters,
pushing their way through dense plant growth
• Eventually they would move from shallow waters
to land
Acanthostega- 365 mya
• First Fish with Digits (8 of
them) on each limb
• Probably Stayed in
shallow waters
– Limbs could not support
weight
Ichthyostega – 360 mya
• First 4-legged land animal- Amphibian
– Stayed near water
What were the Characteristics of
Early Tetrapods?
• It lived in the water
and had a long,
fishy tail
• But its feet had 8
digits (more than
any living tetrapod
has today)
What Happened at the End of the
Devonian Period (360 mya)?
• Mass Extinction #2
• Continental Movement
– Continents had moved over
the South Pole
– Because of the pole’s yearround cold climate, snowfall
accumulated on the
continents, forming glaciers
• The climate became too cold
for many species
• With much of Earth’s water
frozen into glaciers, sea levels
dropped. Lower sea levels
would have robbed life of their
habitat in the shallower oceans.
Who was Impacted by the Mass
Extinction?
• Up to 70% of all marine species may
have died out
– Reefs, and the life they supported, were
devastated
– Many species of corals, brachiopods,
trilobites, and mollusks disappeared
– The armored fishes—placoderms and
ostracoderms—were completely wiped out
Sea Levels and Temp vs. Time