Chapter 12
Pal eozoic Life
: Invertebrates
OVERYIEW
paleozoic was a 300 million year span during which organisms on Earth attained
considerable diversity at sea and on the iand. Th. udnaoc. and retreat of the sea onto and offthe
mntinents; the moviment of the continents from latitude to latitude; the advance and retreat of
glacial iceithe sutruing of the continents; the rise and erosion of mountains-'all contributed to the
Ixternal pressures on th. life forms of Euth. Some organisms adapted; others did not. During the
early stages of marine transgression upon the continentq marine organisms diversified as the
number olniches increased. As time went by there were apparently great pressures brougtr to bear
on some life forms and some became extinct. For example during tlre Cambrian, archa€ocyathids
became extinct. Other groups of organisms zuffered mass extinstion, which occurred drrring the
Late Ordovician, the Late Devoniarq and at the end of the Permian. fire largest of these mass
extinctions ocqrred at the end of the Permiaru when about 50 percelrt of all marine invertebrate
farnilies, 55 percent of all land animals, and 33 pe,rcent of all insects became extinct. Several
*oh*i*1as may be involved in mass extinctionq including rare combinations of ecologically
devastating uuerrtr like meteoritic impacq widespread volcanism and climate changg glaciations
and sea-level changes, and corfrinental motion and mountain building.
The Carrbrian was a time of many evolutionary innovations when most invertebmte groups
evolved. The Ordovician was a time of geat changes in the marine community, especially in the
shelly faunq and it ended in a mass extinction. Silurian and Devonian were zuccessive intervals of
diversificaion and recovery for many invertebrates and a time of vast reef development. Near the
end of the Devonian, a mass extinction decimated the marine communitg especially among reeG
building organisms. Carboniferou$ was atime of great diversification in.the land community The
pefinian *i" ao inte6ral best known for its terminal great mass qrtinction when most of Earth's
species became e*inct during a rdtrer brief intenral.
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fossil remains
found in these rocks, which forrned during
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Which ofthe following organisms ofthe Cambrian are now extinct?
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mollusks
echinoderms
trilobites
brachiopods
archaeocyathids
porifera
bivalves
graptolites
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Hard body parts are useful to the organism in at least wtrat five ways?
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Chapter lzPaleozoic Life: Invertebrates 136
were the most conspicuous element of the Cambrian marine invertebrate
6.
community and made up about
of the total Carnbrian fauna.
fufly recovered before becoming entirely extinct by the end of____-_-____.
8.
Most brachiopods of the Carnbrian were of the
type, which meens that they
lacked
9.
The
brachiopods became abundant during the Ordovician.
were benthonic,
10.
feeders that constructed
sessitre
structures on the sea floor.
I1.
Match the following:
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
rn.
pelagic
plankton
nekton
phytoplankton
benthos
epifauna
epiflora
sessile
mobile
zooplankton
herbivore
carnivore
primary producer
n.
zuspension feeder (filter feeder) o.
transformers and
decomposers
animal on the sea floor
organism lives on the sea floor
free floateq animal
does not move around
eats plants
swimmer
free floater, plant or animal
moves around
lives in the sea
rnanufactures food with light
plant that lives on the sea floor
eats anirnals
makes food
bacteria breaks down what is left
remove and conzume microscopic
plants, animals, and othor food
particles from water
12.
A prirnary food source for the Ordovician
suspension feeders
(filter feeders) was the
phytoplankton group called
Chapter lzPaleozoic Life: Invertebrates 137
is the name of a carnivorous wofin frorn the Burgess Shale.
13.
14.
The organisms which assumed the role
of reef-builders after the demise of
.,
archaeocyathidswere ._-_, _,. . -r
r
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the
and
were the Ordovician planktonic animals carried about by ocean currents.
15.
These fossils are commonly found in
shales.
are small toothJike fossils, which are composed
16.
of
a
mineral.
17.
The climatic change commonly cited as part of the driving mechanism of mass extinction
near the end of the Ordovician is
18.
The effect
of the end-Ordovician
extinotion upon organisms
of the Silurian was
and
19.
Rediversiffing groups
_.2.
20.
, .
of
Silurian were:
____.._.__.___-_
' . - .. , land
After the end-Ordovician mass extinction, the fossil record shows tow more
and
extinctions during the Paleozatc, including
2l
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A Silurian-Devonian eurypterid was an arthropod with
22.
mass
.
and
a cephalopod with detailed suture pattems, appeared during
and rapidly diversified.
_2
24.
and
nruch more severely than other groups
Late Devonian extinctions affected the
of organisrrrs. This mass extinction wa$ more keenly felt in the
reflkn, than
in higher latituds$,
Chapter l2Paleozoic Life: Invertebrates 138
Chapter 13
Paleozoic Life History: Vertebrates and Plants
OVERVIEW
Paleozoic seas abounded with fish and the Paleozoic landscape was dominaed by
amphibians and reptiles. Land plants established themselves for the frst time during the
Ordovician, and ftom these early plants evolved vascular plants and wentually
gJirnnospenns.
Canrbrian seas saw the first primitive vertebrate animalq and by the Ordovician, fish
evolution was well underway. Amphibians first appear dufug the Devonian, and were
extremely abundam upon land by the Pennsylvanian. An wohrtionary innovatiorg the
amniotic egg allowed repiles to colonize the land, beginning during the Mississippian. By
the Permiaq the Srant, fin-backed reptiles were the dominant reptile Soup on land.
Eventually, the mamrnal-ancestors, the mammal-likereptiles ortherapsids appeared on land.
From primitive Ordovician land plantg vascular plams eriolved by the Mddle
Silurian. Seedless vascular plants were quite coflrmon and abundant dtring the
Pennsylvanian. With the arid conditions prevalent durhs the Pennrian in many areas,
gymnosperms evotved to become the dominant plant of the Earth's flora.
sruDYQtIEsrIoNS
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these questions'
Give the best and most appropffie answer to
l.
fragments from a
The otdest knorun vertebrate fossils are phosphatic
jawless armored fish called
.
Late
2,AnaneestorsofthechondatesfoundiuChinais.,wtrichis
(age).
from
is an early tetrapod from Greenland which dates
3.
14.
Amphibians lay
t,ype eggs
in water but reptiles la-v
EIgS
and do not need to refurn to water to reproduce.
15.
The first vertebrates to make the transition to land from the water did so during
16.
The oldest known reptiles evolved during
sediments in ancient hollow tree stumps (in the
and were found in
Formation of Nova
Scotia).
17. All reptiles appear to have evolved from an insect-eating creature known as a
18.
Pelycosaur$? such as Dirnetrodon, were the
reptiles that may have
used their fins or sails to control
19.
20.
List at least four characteristics of the therapsids that made them more mammallike than other repiles.
Therapsids rnay have been endothermic or