Middle Paleozoic Marine Review
• Recovery from end-Ordovician mass extinction
• Strome-tabulate reef community
• Diversification of swimming predators
– Ammonoids, eurypterids
– Fish
Today
• The invasion of land by plants and animals
• Middle Paleozoic paleogeography
Earth History, Ch. 14
1
Earth History, Ch. 14
2
Origin of land plants
• Aquatic plants have got it made in the shade
– Buoyant water helps keep plant upright (no need for
strong roots)
– easy to extract water and nutrients from environment
• Requirements of land plants include:
– Rigid stalk or stem to remain upright
– Roots or buried stem for anchoring in soil
– Roots or buried stem for extracting moisture and
nutrients
Earth History, Ch. 14
3
Land plants
• Earliest land plants were non-vascular (Silurian)
– Consisted of a simple, rigid stem
– Must have lived in marshes or near water because they
lacked true roots, leaves, vascular structure
• Vascular plants originated in late Silurian time
– Possessed conductive tissue to (1) transport water and
nutrients from soil to plant tissues and (2) transport
food manufactured internally through photosynthesis
• Leaf-bearing plants originated in early Devonian
time
Earth History, Ch. 14
4
Vascular
land plants
spore organs
Rhynia (early Devonian)
water-transporting
vascular tissue
nutrient-transporting
vascular tissue
buried horizontal stem
Earth History, Ch. 14
5
Land plants
• Spores are plant reproductive structures
that develop into new adult plants: e.g., as
in modern ferns
• Spore-bearing plants must live in a moist
environment, because sperm must “swim”
to egg during fertilization in alternate
generations of life cycle
• Besides Rhynia, other spore-bearing plants
were lycopods and Archaeopteris—the
first plants to reach tree size
Earth History, Ch. 14
6
Land plants
Devonian lycopods were
mostly small and primitive.
Later, Carboniferous lycopods
grew to tree-size and lived in
swampy forests that were
preserved as coal.
Earth History, Ch. 14
7
Land plants
Archaeopteris,
a 100 ft tall
spore plant with
huge leaves
Earth History, Ch. 14
8
Land plants
• Advent of seeds was a critical
adaptive breakthrough that
permitted land plants to invade
drier areas
– Fertilization is accomplished by airborne pollen in seed plants,
moisture not necessary
• First seed plants were late
Devonian, then they quickly
spread to most terrestrial
environments
Earth History, Ch. 14
9
Geological significance of land
plants
• Coal—economic resource
• Soil stabilization
– Roots hold soil in place and help prevent erosion
– Prior to appearance of widespread land plants in Middle
Paleozoic, most streams were braided (choked with
sediment)
– Soil and roots increase rates of chemical weathering of
silicate minerals (which removes CO2 from
atmosphere)
Earth History, Ch. 14
10
Earth History, Ch. 14
11
Coincidence?
Dramatic decrease in
global CO2 associated
with diversification of
land plants
Earth History, Ch. 14
12
Earth History, Ch. 14
13
Land animals
• Terrestrial invertebrates were common by
early Devonian time
– Scorpions, insects
• First terrestrial vertebrates were
amphibian-like tetrapods (late Devonian)
– Derived from lobe-finned fishes
– Life cycle closely linked to aquatic habitat
Earth History, Ch. 14
14
diversity of vertebrate animals
Earth History, Ch. 14
15
Earth History, Ch. 14
16
“gap”
Earth History, Ch. 14
17
©Jason Downs
Ted Daeschler
Neil Shubin
Earth History, Ch. 14
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Meet Tiktaalik — the “fishapod”
image courtesy of Devoniantimes.org
Earth History, Ch. 14
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©Ted Daeschler
Fish-like traits:
Scales
Fins
Gills and lungs
Tetrapod-like traits:
Neck
Ribs
Flat head
Fin bones
Ear notches
Earth History, Ch. 14
20
©University of Chicago
Earth History, Ch. 14
21
Earth History, Ch. 14
22
Earth History, Ch. 14
©Nature Publishing Group
23
Early
tetrapod
(“fish with legs”)
Earth History, Ch. 14
24
Acanthostega
Earth History, Ch. 14
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Earth History, Ch. 14
26
Land animals
• 1st land-dwelling tetrapod???
Earth History, Ch. 14
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Amphibian
phylogeny
Earth History, Ch. 14
28