GSC 111 Chapter Notes - Chapter 14: Rugosa, Ordovician, Devonian
13 Jan 2017
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Chapter 14: The Middle Paleozoic Word
1. Renewed Diversification of Life
a. After the great mass extinction in the ocean at the close of the Ordovician Period,
many decimated taxa diversified once again, surpassing the Ordovician
evolutionary, radiation
i. Superior reef builders and swimming predators
ii. Plants spread over land
iii. Near the end of the Devonian Period, vertebrate animals invaded the
terrestrial realm
b. Life recovered and expanded in aquatic habitats
i. Most of the marine taxa that had flourished during the Ordovician Period
rediversified after the mass extinction at the end of the Ordovician.
ii. Brachiopods attained higher diversities than before, bivalves invaded
nonmarine habitats
iii. Luxuriant reefs
1. Corals and stromatoporoids diversified in new ways
a. Produced reefs larger than any in the Cambro-Ordovician
age
b. Coral-stome reef community persisted for 120 million
years
c. Assumed enormous population in the Devonian Period
2. In areas subjected to strong wave action, the growth of coral-
strome reef followed a characteristic ecological succession:
a. Sticklike tabulates and rugose corals colonized an area of
subtidal seafloor
b. Low mound was formed when these fragile forms were
encrusted by platy and hemispherical tabulates and colonial
rugose coral
c. As the mound grew up toward the sea surface,
stromatoporoids and algae encrusted the seaward side,
forming a durable ridge. Tabulates and colonial rugose
occupied a zone of quieter water behind the ridge, and
beyond them was a lagoon in which mud-sized sediments
accumulated along with skeletal debris
3. Inhabited by brachiopods and bivalves, snails. Crinoids, bryozoans
iv. New swimming invertebrates
1. Many were predators
2. Most prominent was ammonoids
a. Coiled cephalopod mollusks evolved from a group of
straight-shelled nautiloids during Early Devonian time
3. Another group was eurypterid arthropods
a. Distant relatives of scorpions
b. Swimmers with clams
v. Jawless fishes
1. Adapted to both marine and freshwater conditions
2. Diverse number of fish in the Silurian and Devonian periods
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3. Ostracoderms:
a. Name means bony skin
b. Small animals with paired eyes like those of vertebrates
c. Lacked jaws
d. Covered by bony arm
e. Small mouths allowed them to consume only small items of
food
f. Some dad flattened bellies that were adapted to a life of
scurrying along the bottoms of lakes and rivers while others
had curved bellies
g. Upper fin of the asymmetrical tail was elongate for some
while for others, the bottom was elongate
i. Elongate lower fin suggests a life of more active
swimming
h. Lacked bony internal skeletons
i. Lacked mobile fins
j. Disappeared at the end of the Devonian
vi. Fishes with jaws
1. Appeared in the late Silurian
2. Also marine and freshwater
3. Called acanthodians
a. Elongate animals with numerous fins supported by sharp
spines
b. Features of modern fish
i. Fins were paired
ii. Scales rather than bony plates covered bodies
iii. Had jaws
1. Could prey on other animals
c. Probably predators
d. Declined in the end of the Devonian
4. Jaws evolved from bars that supported the gills of primitive fishes
5. Evolution produced primitive teeth along jaws by enlarging
denticles in the skin that overlay ancestral gill bars
6. Placoderms:
a. On top of food web
b. Heavily armored jaw fish
c. Uppermost Silurian and Lower Devonian freshwater
deposits
d. Did not diversify in ocean until late Devonian
7. Sharks
a. Most important group of fish in Devonian seas
b. Primitive
8. ray-finned fishes:
a. dominated Mesozoic and Cenozoic seas
b. include most familiar marine and freshwater fish
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