EARTH AND ENVIRONMENT THROUGH TIME LABORATORY - EES 1005
LABORATORY SEVEN
PALEOZOIC MARINE FOSSILS
Introduction
Very few fossils have been found
that date before the Paleozoic. During the
PreCambrian there were no skeletal
animals. Nearly all of the fossils that have
been found from the PreCambrian are trace
fossils, and a few soft body impressions.
One of the most important fossils
from the PreCambrian is called a
stromatolite. Stromatolites are trace
fossils of a type of blue-green aglage. This
algae secrets a mucus around its strands,
and in clam water sediments can fall into
the mucus and become stuck. As the algae
grows on top, more and more sediments
become bound to the mass, forming a
cabbage-like mound. Blue-green algae,
which produces oxygen (O2) as a waste
product during photosynthesis, was one of
the first organisms to evolve,
approximately 3,500 million years ago,
and had a few predators until the
Cambrian, approximately 570 million
years ago. During that interim, enough
free oxygen was produced and
accumulated in the atmosphere, that new
life forms were able to evolve.
Stromatolites become increasingly rare
throughout the Phanerozoic, because
organisms evolved which consume the
mucus on the algae before the sediments
accumulate.
The beginning of the Paleozoic
marks the first appearance of organisms
with hard pars. This lab will introduce
some of the important fossils in the
geological fossil record. You will be
expected to identify the italicized fossils
for the next quiz, and know the phylum for
each. Some of these are index fossils
which are important tools.
Index fossils are fossils which are very useful in correlating and dating rock beds. In
order for a fossil to be a good index fossil, it must be: 1) geologically short lived,
2) abundant during its existence, and 3) widespread in its occurrence.
Paleozoic Fossils
This week we begin working on the Paleozoic fossil shelf for your notebook.
Remember to include the age ranges (pgs. 32-33) when requested.
PHYLUM ARTHROPODA
Cl. Trilobita (Cambrian - Permian)
Trilobites had a hard segmented
body with an outer shell made of chitin,
which preserves fairly easily. As the
trilobites grew, they shed this exoskeleton
and formed a new one. Their body was
divided into three lobes: cephalon (head),
thorax (body), and pygidium (tail). Their
fossil remains often consist of
disarticulated heads, tails, or body
segments. They can also be found rolled
up into a ball. Trilobites were most
abundant during the Cambrian and
Ordovician.
PHYLUM BRACHIOPODA
G. Brachiopods (Cambrian - Recent,
common in Paleozoic)
Brachiopods were extremely
common in the Paleozoic. They are easily
mistaken for bivalves because they are
enclosed by two hinged valves, but their
soft parts are fundamentally different.
They show bilateral symmetry like the
bivalves, however they symmetry is
perpendicular to the plane of separation,
whereas in bivalves the plane of symmetry
is the same plane as the plane of
separation. In most species, one valve has
an opening at its apex, through which a
stalk-like organ protrudes, anchoring the
animal to stable surfaces.
Articulate brachiopods have a
mechanical "tooth & socket" hinge which
can keep the shells together even after they
die.
Inarticulate brachiopods are held
together by muscle, so the shells usually
fall apart from each other when they die.
PHYLUM BRYOZOA
G. "Branching" Bryozoans (Ordovician Recent)
Bryozoans are microscopic
organisms which live in colonies. They
look like corals, however they have a
complex anatomy. A colony consists of
individual zooids which are asexually
budded clones of the original. The
branching bryozoans were common in the
Paleozoic.
The Archimedes bryozoan was a
particular genus common in the
Mississippian, and makes an excellent
index fossil: it was abundant, widespread,
and had a very recognizable shape. It had
a lacy colony attached to a spiral-shaped
support structure.
Paleozoic Fossils
PHYLUM CNIDARIA
Corals are simple animals with no organs.
They have just a mouth surrounded by
tentacles, a gut cavity, simple muscles, and
a nerve network. Specialized stinging cells
called cnematocysts aid in capturing prey,
defense, and aggression. True corals have
aragonite or calcite skeletons and are also
commonly fossilized. Jellyfish are also in
this phylum, but are rarely fossilized.
G. Rugose Corals (Ordovician - Permian)
Rugose corals contained a cup-like
depression in which the polyp lived. Its
gut cavity was radially divided by
septa.The septa can be seen by looking at
the end of the fossilized skeleton. Rugose
corals are found as "horn corals" - the
remains of a solitary organism, or as a
group of individuals cemented together
forming a colony.
G. Tabulate Corals (Ordovician Permian)
Tabulate corals were similar to
rugose corals, but did not have divided
chambers and were exclusively colonial.
PHYLUM ECHINODERMATA
Echinoderms are easily recognized
by their unique five-fold symmetry. They
feature a body cavity typically enclosed by
a calyx or similar structure of plates which
cleave like calcite. All echinoderms have a
circulatory system in which the fluid salt
content is balanced with that of sea water
by means of suckers on their tube feet.
Cl. Crinoidea (Ordovician - Recent,
common in Mississippian)
Crinoids live on the shallow ocean
bottom attached by a stem and
superficially resemble sea lilies. A calyx
of five-fold symmetry encloses their
globular body. Their food gathering arms
have tube feet and resemble feathers. The
arms and stems consist of disc-like plates
called columnals. Crinoids were so so
common during the Mississippian that
some limestones of this period are
composed almost entirely of broken up
crinoid stems. These limestones get their
own name: encrinite.
Cl. Blastoidea (Ordovician - Permian, very
common in the Mississippian)
Blastoids looked similar to crinoids
except the plates on their calyx were
somewhat flatter and had a more distinct
five-fold pattern. Their arms were located
along the margins of these plates. They
were also extremely common during the
Mississippian.
G. Starfish (Ordovician - Recent)
Starfish are composed of soft body
parts surrounded by smaller spiny plates
which break apart upon their death. They
feed using their tube feet. Most starfish
have five arms.
Paleozoic Fossils
PHYLUM HEMICHORDATA
Cl. Graptolita (Cambrian - Mississippian,
most common in the Ordovician)
Graptolites were small colonial
organisms that floated in the ocean. They
are typically preserved by carbonization,
appearing as black saw-tooth, pencil-like
lines. They are good index fossils for the
Ordovician and Silurian.
PHYLUM MOLLUSCA
Cl. Bivalvia (Ordovician - Recent)
Bivalves have two shells that are
mirror images of each other. They have a
muscular foot that may be used for
movement. Clams and oysters are
bivalves.
Cl. Gastropoda (Cambrian - Recent)
Gastropods are the most widespread,
diverse, and abundant molluscan class.
Snails and slugs are in this class. Shelled
gastropods have a clockwise rotation or
twisting of an otherwise bilaterally
symmetrical body. Their shells can be
coiled (planar or helical) but there are no
septa.
Cl. Cephalopoda (Cambrian - Recent)
Cephalopods are predatory
invertebrates with bilateral symmetry.
Shelled cephalopods live in the outer
portion of a shell which is divided into
chambers by a series of septa. The contact
between the septa and the shell interior is
called the suture. The unoccupied
chambers are filled with gas and liquid.
These chambers are connected by a tissuelined tube (siphuncle) and cephalopods
can control their position in the water by
regulating the distribution of the liquid.
G. Nautiloid (Cambrian - Recent)
Nautiloids have a straight, simple
suture pattern on the outside of their shell,
marking where the inside is divided into
chambers. They may be straight (conar) or
coiled (planar).
G. Ammonoid (Devonian - Cretaceous)
Ammonoids evolved from
Nautiloids, developing a complex suture
pattern that gave more support to the shell,
allowing them to feed in deeper waters.
They are usually coiled, but may be
straight (cone-shaped).
Paleozoic Fossils
PHYLUM PORIFERA
G. Stromatoporoid (Cambrian - Recent,
most common in the Ordovician and
Devonian)
Stromatoporoids were a colonial
group of simple multicellular animals
that secreted a calcareous laminated
skeleton. They were most abundant during
the Ordovician and Devonian. These
sponges had a hard skeleton and were reef
formers.
PHYLUM PROTOZOA
Cl. Foraminifera (Ordovician - Recent)
Forams are microscopic single
celled organisms made up of calcium
carbonate.
G. Fusilinids (Pennsylvanian - Permian)
These are the most common
Paleozoic forams, and make good index
fossils.
Cl. Radiolaria (PreCambrian - Recent)
Radiolarians are microscopic, single
celled, free floating organisms which drop
plates of silica (SiO2) into the ocean,
forming oceanic deposits of chert.