PALEO LAB # 2, PAGE 1
PALEO LAB # II - PROTEROZOIC AND EARLY PALEOZOIC FOSSILS AND
MICROPALEONTOLOGY
Although I do not expect you to generate art-quality renderings of fossils, please be neat with
your art and make the drawings large enough where I (and you) can see the structures.
Introduction to Fossil Labs
The paleontology labs will concentrate on the recognition of the most important types of fossils,
their Biostratigraphic Ranges (when they evolved and at what time they became extinct), their
Habitats (the place where they lived), and their Life Habits (the way they went about their daily
activities, primarily locomotion and food-gathering).
In the paleontology labs we will be concerned with several subdisciplines of paleontology.
We will observe the effects of organisms on sediments. The study of tracks, trails and burrows
left by ancient organisms, termed Ichnology, is an important aspect of paleontology.
Micropaleontology is the study of fossils that are too small to study without the aid of a
microscope. Micropaleontology has become an extremely valuable tool in the search for fossil
fuels. The large rotary drills used in recovering petroleum and testing for the presence of other
fossil fuels tends to destroy all traces of ancient organisms except for microfossils. These little
organisms are important for defining the age of the sediments and the paleoenvironments in
which oil might be discovered. Primarily, micropaleontologists study protozoans and algae.
However, some types of crustaceans, bryozoans and gastropods are best observed by using a
microscope and thus fall in the realm of micropaleontology. Another field of paleontology is
Paleobotany, the study of fossil plants. Palynology, the study of spores, pollen and other "plant"
microfossils, is a science that is related to both micropaleontology and paleobotany and is also
widely utilized in the search for fossil fuels. Invertebrate Paleontology is the study of fossil
animals lacking a backbone, and includes most of what we refer to as the "lower animals". The
study of fossil vertebrate animals (such as fish, amphibians, reptiles, birds and mammals) is
termed Vertebrate Paleontology.
Taxonomy
Taxonomy is the science of classifying organisms. For hundreds of years organisms were
divided into two groups; the plants and animals. However, as the studies of all living organisms
progressed, it was discovered that not all life forms fit neatly into one of these two groups.
Therefore, five major groups of organisms (Kingdoms) are generally recognized; Monera
(prokaryotes; organisms with a very primitive cellular construction; these organisms are often
divided into two Domains, the Archaebacteria and Eubacteria), Protoctista/Protista [one-celled
(unicellular) eukaryotes; organisms with advanced cellular features such as nuclear membranes,
mitochondria, chloroplasts, vacuoles and golgi apparati], Fungi, Metaphyta/Plantae (plants) and
Metazoa/Animalia (animals).
Each kingdom may be divided into smaller groupings, termed Phyla (singular is Phylum; in
plants this subgrouping is termed a Division). A Phylum or Division may be divided into
Classes, which may be grouped into Orders, and orders may be subdivided into Families. Every
known organism has been given a Genus and Species name, derived from Latin or Greek and
underlined or italicized. Although the world is separated by many political boundaries and
PALEO LAB # 2, PAGE 2
languages, the genus and species name for any taxon (the particular classification category of an
organism; plural is taxa) remains constant. In this way, communication between scientists
concerned with each set of plants or animals is much simplified. The following table illustrates
how several organisms are named using Taxonomic Classification:
UNIT
Kingdom
Phylum/Division
Class
Order
Family
Genus
Species
HUMAN
Metazoa
Chordata
Mammalia
Primates
Hominidae
Homo
sapiens
CLAM
Metazoa
Mollusca
Bivalvia
Eulamellibranchia
Veneridae
Venus
mercenaria
ROSE
Metaphyta
Tracheophyta
Angiospermae
Dicotyledoneae
Rosaceae
Rosa
multiflora
Identification of Fossils
The student may be slightly overwhelmed by the abundance of seemingly unpronouncable
names and complexity of features encountered in paleontology. However, a little knowledge of
paleontology will help you interpret many aspects of Earth history. Our first step will be learning
to recognize the major phyla and classes of fossils we may encounter in the field. This is the
primary purpose of these introductory labs on paleontology.
Early Fossils
Kingdom Monera
The Kingdom Monera includes bacteria (constituting several divisions including the
fermenting bacteria, sulfate-reducing bacteria and anaerobic photosynthetic bacteria) and bluegreen algae (Division Cyanobacteria). Of these, the cyanobacteria are much better known from
the fossil record. The monerans are prokaryotes in which the cells lack membrane-bound nuclei,
mitochondria, chloroplasts and similar organelles and that reproduce by simple division. Some
authors subdivide prokaryotes (monerans) into two kingdoms, the Kingdom Archaebacteria and
Eubacteria. This is based on the chemistry of their cell walls and membranes, and structure of
their RNA. Possible fossils of blue-green algae have been found in Western Australia which date
to approximately 3.4 to 3.5 billion years before the present. Both fossil bacteria and blue-green
algae have been recovered from the Fig Tree Formation of South Africa, which are
approximately 3.1 billion years old.
It is amazing (to me, anyway) that prokaryotes are ever preserved in the fossil record. This
preservation may be in the form of compressions (flattened, two-dimensional organic residues,
especially found in shales) or as permineralized microfossils (encased in fine-grained minerals
such as chert or microcrystalline quartz which tends to produce three-dimensional preservation).
Most fossil prokaryotes are preserved by permineralization in stromatolitic cherts.
Cyanobacteria may be divided into a number of Orders; the Chroococcales,
Chamaesiphonales, Pleuocapsales, Nostocales and Stigonematales. In turn, these may be divided
into two broad categories (1) Unicellular of colonial forms, in which coccoid, spheroidal or
ellipsoidal cells are commonly embedded in a mucilagenous sheath (Chroococcales) or with cells
differentiated into a base and apex (Chamesiphonales) and (2) filamentous forms with sheath-
PALEO LAB # 2, PAGE 3
enclosed cell pairs or colonies (Pleurocapsales) or with elongate, barrel- or disc-shaped cells
commonly enclosed by a branching (Stigonematales) or nonbranching (Nostocales) tubular
mucilagenous sheaths. Among unicellular and colonial forms, the chroococcaleans are most
abundant as fossils and extend well back into the Proterozoic (Late Precambrian). Some reports
indicate that this group may extend back to 3.3-3.5 billion years before the present. Among
filamentous cyanobacteria, nostocaleans (especially members of the Oscillatoriaceae) are most
abundant as fossils and are well represented in the Late and Middle Proterozoic and throughout
the Phanerozoic. Possible notocaleans have also been reported in the Early Archean (Early
Precambrian).
EXERCISE # 1 - Refer to the discussion above and the power point slides. For each of the slides
of modern Cyanobacteria provided (TSU PB 007 thru PB 010), sketch and classify each as
precisely as possible.
EXERCISE # 2 - Observe the slide from the Gunflint Chert (TSU PB 011), a Proterozoic
Formation dating to about 1.9 billion years. Using the same classification system as in Exercise #
1, identify the type(s) of Cyanobacteria in this slide.
Stromatolites are structures produced by blue-green algae which represent some of the oldest
fossils known. However, they do not typically preserve the microfossils that built them. Due to
recrystallization of the stromatolite during formation of a carbonate rock the fossils tend to be
destroyed. Near Bulawayo in Southern Zimbabwe stromatolites have been found in limestones
dating at 2.8 billion years before the present. The Warawoona Group of Western Australia has
yielded even older stromatolite-like fossils, dating from 3.4 to 3.5 billion years before the
present. The study of Carbon 12/ Carbon 13 ratios in Archean-age rocks suggests the biological
fixation of carbon dioxide by these organisms through photosynthesis and represents the earliest
records of oxygen-producing organisms on the planet.
Stromatolites are produced by "mucoid algae" which manufacture an organic glue. Finegrained carbonate mud is glued to the organism to give the microorganisms support and
protection. Stromatolites are most often found on muddy substrates in shallow marine waters
(usually at or slightly above the intertidal zone) and salt lakes. However, some stromatolites
occur in deep marine environments and numerous freshwater forms have also been described. In
fact, stromatolites can form in almost any free-standing body of water, providing the following
conditions are met: (i) the environment is suitable for the growth of the appropriate
microorganisms; (ii) the rate of growth of the constructing microorganisms exceeds their rate of
consumption by other organisms (iii) the rate of sedimentation is sufficient to produce a
preservable structure but is not so great as to prevent colonization by microorganisms and (iv) the
stromatolites accrete (grow upward and outward) faster than they can be destroyed by boring
organisms and erosive and other mechanical and chemical forces.
As stromatolites are useful paleoecologic indicators they can be used reliably for correlation
of similar environmental settings. Stromatolites can therefore be useful for intrabasinal
correlation. Although the Russians are working on it, there is some question as to whether or not
stromatolites are applicable to interbasinal stratigraphic correlation (i.e. on an intercontinental,
global scale). As yet, this has not been resolved. However, as stromatolites are the most
common large fossils of the Precambrian, it would be terrific if they could be used for such
PALEO LAB # 2, PAGE 4
correlation.
For classification purposes, stromatolite "Groups" are typically defined by the gross
morphology of the individual structure. Three principal categories can be distinguished.
(1) stratiform (e.g. Group Stratifera)
(2) columnar (e.g., unbranched cylindrical columns, Group Gymnosolen, and branching columnar
structures such as those included in Group Baicalia)
(3) spheroidal (e.g. spherical-shaped oncolites such as those included in Group Osagia)
Of these groups, Stratifera and columnar-domical structures (Group Collennella) are of
particularly common occurrence.
These groups can, in general, also be correlated with environmental conditions. For example,
flat-lying, tabular stromatolites (e.g. Stratifera) are characteristic of very low energy, quiescent
environments such as evaporitic salt-flats, quiet lagoons and the like. Domical types (e.g.,
Collennella) tend to occur in intertidal, relatively higher energy environments in which tidal
scour inhibits inter-column growth of microbial mats. Oncolites, produced commonly by
disruption of microbial mats and repeated "rolling" of the mat fragment that permits growth and
lamina formation on sequentially exposed uppermost surfaces, are similarly typical of relatively
high energy (wave-disturbed) settings. High relief conical stromatolites (e.g. Conophyton,
Jacutophyton) are regarded by many workers as relatively deep water, low light-intensity
environments.
EXERCISE # 3 - Refer to the discussion above and the power point slides. For each of the
stromatolites provided (TSU PB 004, PB 005, PB 031), classify the specimen as precisely as
possible and determine the possible paleoenvironmental significance of each.
Kingdom Fungi
The Fungi consist of one division, the Eumycota. These organisms are often found as minute
filament- or club-like fossils within the fossil remains of decayed plants. Many fungi feed on
decaying organic matter (Saprophytes or Scavengers) and others are Parasites. Although some
organic structures from the late Precambrian have been referred to the Fungi, the earliest
nondisputed Eumycota have been found in decayed tissues of vascular plants from the Devonian.
Kingdom Protoctista/Protista
Several photosynthetic divisions of Protoctista are studied by botanists, and a number of these
have a substantial fossil record. These include the divisions Phaeophyta (brown algae),
Rhodophyta (red algae), Bacillariophyta (diatoms), Haptophyta (calcareous nannoplankton or
coccoliths), Dinoflagellata (dinoflagellates) and Chlorophyta (grass-green algae). The
Foraminiferida (foraminiferans) and Actinopoda (radiolarians) are often termed "protozoans"
(see discussion below). These protists differ from the "algae" mentioned above as they are not
autotrophic organisms (produce their own food) but are instead heterotrophic (obtain their food
by feeding on other organisms). We will discuss the autotrophic protists and more heterotrophic
protists in a later lab. However, one of the heterotrophic groups of protists, the protozoan group
Foraminiferida, are especially abundant and important in Paleozoic rocks.
Protozoans are unicellular or acellular protists within the Kingdom Protoctista which are
aquatic or parasitic in habit. The most important protozoans in the fossil record are the
foraminifers and radiolarians, which move by means of flowing protoplasmic extensions or
PALEO LAB # 2, PAGE 5
pseudopodia.
1.Grypania
The oldest-known probable eukaryote is the corkscrew-shaped, cylindrical megascopic
colonial alga Grypania, from the Early Proterozoic of Michigan. Although the relationships of
Grypania are poorly-established, I place it here with the protistans for convenience.
EXERCISE # 4 - Observe the specimen of Grypania spiralis, from the Negaunee Iron Formation
from near Marquette, Michigan (TSU PB 003). Pretty impressive, huh? Grypania is variously
classified as belonging to either the Kingdoms Protista/Protoctista or Metaphyta. Why might
Grypania be considered a protistan? What characteristics of the Metaphyta does G. spiralis
possess?
2. Division Rhodophyta
The Rhodophyta, or red algae, is an important group of calcium-carbonate secreting
organisms. Early possible representatives of the group are the phylloid algae. These leaf-like
algae often formed small carbonate banks in Carboniferous seas which now are important
petroleum reservoirs. Phylloid algae often form thin, curved structures on carbonate rock surfaces
that are referred to informally as "potato chips". The most important group of rhodophytes in
modern oceans is the Superfamily Corallinaceae (Late Paleozoic? Jurassic-Recent), often times
termed coralline algae. The skeletal tissue of these algae, which consists of a two-layered
cellular structure, often forms the limestone framework for seaward-facing reef ridges. An
earlier superfamily, the Solenoporaceae (Ordovician-Miocene) are similar to coralline algae (they
may be ancestral to them), but are not differentiated into two layers.
EXERCISE # 5 - Examine the specimen of Winchell Limestone (TSU PB 002), an Upper
Pennsylvanian (Canyon Group; Missourian) carbonate bank deposit that outcrops near Graham,
Texas. What morphological characteristic would lead us to believe that rhodophyte specimens
are present within the limestone?
3. Division Chlorophyta
We have discussed the significance of green algae in previous labs and lectures, as this
division is probably ancestral to land plants. However, most members of the Chlorophyta do not
secrete hard tissues and are therefore not typically fossilized. A major exception is the aragonitesecreting codiacean algae (Jurassic-Recent). The tiny spicules of this group are major
contributors to carbonate sediments in modern tropical oceans.
Other possible representatives of the Chlorophyta are the receptaculitids (OrdovicianPermian). Because of their external morphology, these sac-like structures are often termed
"sunflower fossils". However, the classification of the receptaculitids has not been adequately
established. Some paleontologists place the receptaculitids within the blue-green algae
(Cyanobacteria), and there are other classifications that include them within the "pleosponges"
(as a sister group to the archaeocyathids)! When scientists cannot even decide in which kingdom
a taxon should be placed, you know that we still have some issues to be resolved in paleontology.
EXERCISE # 6 - Sketch a portion of the receptaculitid specimen Receptaculites occidentalis
PALEO LAB # 2, PAGE 6
from the Ordovician of Virginia (TSU PB 001). Note the presence of the pillar-like structures.
Acritarchs - It is probable that most "acritarchs" represent the reproductive structures (termed
cysts) of green algae, although this term has also been applied to many groups of planktonic algal
cysts ranging in age from Proterozoic thru the Jurassic. Acritarchs are the first true
palynomorphs, with "resistant-walled" coverings composed of material similar to that protecting
later pollen and spores (termed sporopollenin). The oldest acritarchs consist of simple spheres,
and are termed sphaeromorphs. By late Cambrian times acanthomorphs become common, in
which the spherical main body bears processes ranging from spines, to penis-shaped processes
(baculate) to complex branching structures.
EXERCISE # 7 - Using a petrographic microscope, sketch a couple of the dominant acritarch
types from the slides provided (TSU PB 013, PB 016, PB 18 thru PB 21, PB 23 thru PB 26).
Label each drawing as representing an acanthomorph or sphaeromorph.
4. Division? Chitinozoa
The Chitinozoa are a group of extinct microscopic animals whose systematic position is not
known, although they probably represent eucaryotic algae. They have hollow, organic-walled
tests that are radially symmetrical about a central longitudinal axis and closed at one end; in short
they look like minute bottles. Individual tests measure 50-2000 microns in length. They were
named after the chitinous-like appearance of their tests by their discoverer, Alfred Eisenack.
The Chitinozoa evolved rapidly during the Ordovician, Silurian and Devonian periods. They
were exclusively marine and formed an important part of the small animal life in the oceans of
the time. There is no general agreement as to whether chitinozoans were benthic or planktonic.
It is possible that some chitinozoans were planktonic while others were benthic, or that the
chitinozoan life cycle involved planktonic and benthic stages. They are found in organic residues
from virtually all types of marine sedimentary rocks and consequently are useful in stratigraphy
for dating and correlating rocks of Ordovician, Silurian and Devonian age.
EXERCISE # 8 - Sketch one of the chitinozoans from slides TSU PB 018 thru TSU PB 021 or
TSU PB 024 thru TSU PB 026. Label the following features: aboral end, aperture, chamber,
flanks, operculum, oral end, oral tube, pore, prosome, and shoulder.
5. Phylum Foraminiferida
The foraminiferans (commonly referred to as "forams") secrete shells (tests) composed of
membraneous, pseudochitinous or calcareous material or agglutinated ("glued-together")
sedimentary particles. The presence of a network of anastamosing pseudopodia sets them off
from other protozoans. Many of the foraminifera are vagrant benthonic, using their pseudopods
to propel themselves at speeds of up to one centimeter per hour (WOW!). Other forams are
sessile benthonic, while others are planktonic, moving through the water column by changing the
gas content within their protoplasm. Though most foraminifers are marine, some are adapted to
existence in brackish water bodies, and one primitive family is known to live in fresh water.
They range in size from 0.02 to 140 mm (most however are less than 1 mm in size) and occur at
all depths and latitudes in modern seas. Fossil representatives are common in marine
sedimentary rocks of all systems from the Cambrian to Holocene (Recent).
PALEO LAB # 2, PAGE 7
Fusulinids - The Fusulinids were a group of small to very large (up to 10cm!), reef-dwelling
forams that lived during the Mississippian to Permian periods. During their 100 million year
existence, they evolved more than 150 genera and 6000 species before declining in the latter part
of the Permian and becoming extinct near the end of that period. Because of their restricted
biostratigraphic range and limited ecological distribution, they are very useful indicators for the
geologist. In fact, the Pennsylvanian and Permian Systems are divided into biostratigraphic
zones primarily on the basis of fusulinid genera.
The fusuline test is microgranular, calcareous, perforate (with tiny holes) with greater or
lesser amounts of foreign material incorporated into the calcareous walls. The wall structure is
of primary classificatory importance in fusulinids. Fusulinids have no aperture (main opening
from the chamber to the exterior) but had access to the exterior through numerous septal pores
found in the antetheca. The test is commonly planispirally coiled (coiled in a single plane). This
is coiled about an axis which is short in primitive genera, but several times the length of the test
diameter in more advanced genera. Triticites, a species that you will work with in lab, occupies
an intermediate position in this fusulinid "evolutionary scale". Its axis of coiling is elongate,
although not to such an extent as that of more specialized genera.
As a group, fusulinids are characterized by rapid evolutionary changes in distinctive
morphological features and this has enabled paleontologists to establish detailed stratigraphic
zonations and phylogenies for them. Most of these features are studied in oriented thin sections.
The most useful of these is an axial section oriented so that the section lies in the axis of coiling
and thus passes through the proloculus. A sagittal section is perpendicular to the axial section
and also passes through the proloculus. It shows the spiral shape of the shell and the outline of
each chamber. A third type of oriented section, the tangential section, is cut so the plane of the
section is parallel, or nearly so, to the axis of coiling but cuts a plane just above the outer surface
of a previous volution. Tangential sections show the relationships at the toes of septal folds,
particularly whether these toes have been resorbed to form little passageways called caniculi.
EXERCISE # 9 - Using a microscope, draw a view of the exterior and a couple of thin section
views of Triticites (TSU IP 007 thru IP 011, TSU IP 041). Label the type of section viewed; see
above). Label the following morphological features: antetheca, external furrow, proloculus,
septal fluting, septal pore, and spirotheca.
KINGDOM ANIMALIA (METAZOA)
The Animalia consists of multicellular organisms that obtain their nutrition by consuming
other organisms (i.e. heterotrophs). The Animalia includes a wide variety of invertebrate phyla
and the chordates.
The Ediacara Fauna, or Vendobionta
During the Late Proterozoic, multicelled animals became an important part of the fauna.
Among the earliest well-preserved fossil assemblages is the Ediacara Fauna, named for a locality
within southern Australia. The Ediacara Fauna consists of flattened animals, many of which are
characterized by a foliated or quilted (infolded) body construction. A debate has occurred
between groups of paleontologists as to the significance of the Ediacara Fauna. Some place these
Vendian fossils within modern groups of animals, such as coelenterates, annelid worms,
PALEO LAB # 2, PAGE 8
arthopods, and crustaceans, although recognizing that some of the Vendobionta cannot be
referred to any known modern form. A second group of scientists, headed by the German
paleontologist Adolf Seilacher, believe that the organization of the Ediacara animals does not
match any known modern group. Therefore, in their view the Vendobionta represents a separate,
distinct branch of animal evolution. Stay tuned!
EXERCISE # 10 - Study the casts of the Proterozoic-age taxa Charnia (TSU IP 004),
Dickinsonia (TSU IP 001), Spriggina (TSU IP 002) and Tribrachidium (TSU IP 003). What
features indicate that these organisms may be referred to the Ediacara Fauna, or Vendobionta?
What modern group(s) of organisms have a body construction similar to these "vendobionts"?
The Criconarids, or Conioconchia
The criconarids consist of small (up to 3 inch-long), cone-shaped fossils ranging in age from
Ordovician through Devonian. The major group of criconarids are the tentaculitids (Order
Tentaculitida), which consist of narrowly-conical, thick-walled shells that consist of several
layers. The shell also bears transverse rings. Although a number of scientists consider the
criconarids to represent primitive molluscs, other paleontologists have placed them within the
annelid worms and others consider them to represent a distinct phylum.
EXERCISE # 11 - Using a microscope, sketch one of the tentaculitids provided (TSU IP 005, IP
006, IP 462). Label the apical region, median region and apertural region. Also label a transverse
ring and the aperture.
Phylum Hyolitha
The hyoliths are operculate calcareous conical shells that appear at the same time as molluscs
in earliest Cambrian strata and disappear at the end of the Permian. They have often been placed
within the Mollusca, although now they are typically considered a separate phylum as their
conical exoskeleton does not seem to be homologous to the primitively-dorsal molluscan shell.
Hyoliths are therefore typically placed in a separate extinct phylum that is closely related to the
Mollusca. Features of the hyolith shells considered especially similar to those of molluscs
include shape, nature of the muscle scars and the crossed-lamellar microstructure of the shells.
EXERCISE # 12 - Using a microscope, sketch an anterolateral view of one of the hyolithids
provided (TSU IP 038 thru IP 040). Label conch, operculum, dorsal, ventral, anterior and
posterior. Reconstruct a helen lateral to the conch.
The "Small Shelly Fauna", or Tommotian Fauna
The first abundant record of fossils with "hard parts" appears at the base of the Cambrian.
Here, we encounter the remains of numerous mollusc-like shells, calcareous and siliceous
spicules of sponges and probably soft corals, arthropod carapaces, calcareous cups of sponge-like
archaeocyathans, shells of brachiopods and brachiopod-like animals, as well as various tooth-like
objects. The general term for this distinctive Cambrian fauna is the "small shelly fauna", the
"Tommotion fauna" or simply "SSFs".
The tooth-shaped Tommotian elements, termed sclerites, consist of calcium carbonate or
calcium phosphate fossils that may have articulated to form external coverings on some as-yet-
PALEO LAB # 2, PAGE 9
unknown invertebrates, much like links of chain mail formed armor coverings for Medieval
knights. The term "tommotiid" refers to phosphatic sclerites that evidently articulated to form
such an exoskeleton.
EXERCISE # 13 - Utilizing a binocular microscope, observe one of the Cambrian-age rock slabs
bearing Tommotian fossils. Sketch a couple of the sclerites present in sample TSU IP 012. What
other phylum/phyla of fossils may be observed on these slabs?
Phylum Archaeocyatha
Archaeocyathans are an extinct phylum of exclusively marine, conical, calcareous organisms
known primarily from the Early Cambrian. During the middle portion of the Early Cambrian
they gained a nearly worldwide distribution, but became extinct during the early Middle
Cambrian. Archaeocyathans were one of the first phyla to use calcium carbonate as skeletal
material and formed the first reef-like deposits of the Paleozoic. Their paleoecology was quite
reminiscent of modern hermatypic corals, as they are often found closely associated with fossil
algae (and were therefore symbiotic?), they preferred carbonate facies, and were most abundant
at water depths of 20 to 30 meters in agitated marine waters.
The internal structure of archaeocyathids is crucial in their study and transverse, longitudinal
and tangential sections are used to define their morphology. The typical archaeocyathan skeleton
(Cup) is a solitary, highly-porous, double-walled inverted cone. Between the inner and outer
walls is a space (the Intervallum). It is subdivided into elongate chambers (Loculi) by radial
partitions (Septa). The inner wall surrounds and defines the Central Cavity. The larger or upper
end of the cup is typically open and the lower end (Tip) is closed and often buried in the substrate
or held by rootlike Holdfasts. There are two classes of Archaeocyatha. The Regulares are
characterized by septa, tabulae or both in the intervallum; the Irregulares are characterized by the
presence of Dissepiments (curved, cyst-like plates) in the intervallum.
EXERCISE # 14 - Using a microscope, sketch one longitudinal and one transverse section from
the archaeocyathid specimens provided (TSU IP 012, IP 014, IP 017, IP 031 thru IP 037); label
outer wall, inner wall, central cavity, loculum, intervallum and septum. Does the specimen
belong to the Regulares or Irregulares?
Phylum Porifera
The skeletons of sponges (Phylum Porifera) have been used for thousands of years for bathing
and cleaning. Although sponges have been widely utilized, it was not until approximately a
century ago that they were accepted as belonging to the animal kingdom.
Sponges are among the simplest of multicellular organisms. They lack a mouth or
differentiated organs. They do not have organized digestive, nervous or muscular systems and,
as such, appear as relatively uncoordinated groups of various cells. Sponges are sessile
benthonic organisms that may be found in both fresh and marine waters. However, most recent
sponges are found in marine waters with salinities between 30 and 40 parts per thousand.
The name Porifera means "pore-bearer". Upon close inspection of a sponge, you will notice
thousands of tiny holes in the walls of a sponge through which water enters and microscopic
plankton is filtered out and digested. Because sponges are suspension feeders, they are generally
confined to clear water in which there is no suspended mud to clog their pores. The greatest
PALEO LAB # 2, PAGE 10
densities of living sponge populations are in the lower portions of the littoral zone (low tide to
high tide). However, sponges can be found at almost all depths and therefore are not entirely
accurate as paleobathymetric indicators, although individual species of sponges typically have
well-defined limits in terms of temperature, salinity, currents, turbidity tolerance and other
environmental factors.
Shapes of sponges may often be indicative of their environments. For example, chimneyshaped sponges generally occur where currents are moderately strong. The tubular form aids in
"sucking" water through the system, much as wind across the top of a chimney moves effluents
up the stack. Massive hemispherical and low platter-shaped sponges tend to be common in areas
of moderately agitated water. Conical or cup-shaped forms tend to be common in areas of
intermediate current intensity.
Sponges secrete needle-like Spicules that form a skeletal framework which supports the soft
cellular mass, keeps the canals from collapsing, and enables the sponge to grow to a considerable
size. The spicules vary considerably in form. One sponge may have spicules of several shapes
but as these are fairly constant for a particular species, they serve as an important criterion in
identification. In fact, sponge spicules serve as the principle documentation of the phylum in the
fossil record and therefore spicule form is a very important aspect of fossil sponge study.
EXERCISE # 15 - Observe the slide (TSU IP 028) of the sponge spicules through the
microscope. Sketch as many types of sponge spicules from the slide as possible and, referring to
the figure included here, identify them as precisely as possible.
Classification of Sponges
Four classes of sponges are recognized based largely upon composition and symmetry of
skeletal elements. In addition, several other groups of spongeomorphs are "lumped" within these
classes or placed as separate, distinct taxa.
1. Class Calcarea
Those sponges with calcareous spicules or skeletons are often placed in the Class Calcarea, a
group which ranges from Cambrian to Recent (but these ranges depend on which classification
system you use; see below). Study of fossil groups of calcareous sponges seems to indicate that
several types that have traditionally been placed within the Calcarea may not belong. A good
example of this is the Heteractinids. This is a relatively minor group of calcareous sponges,
although a member of this group (Astraeospongium) is one of the most commonly studied fossil
sponges in the world. Astraeospongium is a thick-walled and bowl-shaped fossil sponge with an
upper concave surface; its lower side is convex. The fossil consists of a mass of relatively large,
calcareous cruciform spicules with six of the rays disposed in the same plane; the two rays
projecting at right angles to this plane are reduced to short, button-like prominences in surface
spicules. The spicules were supposedly arranged with the plane containing the six rays more or
less parallel to the surface of the sponge. This form is an important rock-former in Tennessee
and northern Illinois. Astraeospongium is also an important guide fossil in both the Silurian of
North America and the Devonian of Europe.
EXERCISE # 16 - Draw upper and side views of Astraeospongium (TSU IP 019). Also draw a
generalized, enlarged view of one of its spicules. Label a spicule.
PALEO LAB # 2, PAGE 11
EXERCISE # 17 - Girtyocoelia belongs to the suborder Sycones, calcareous sponges
characterized by the presence of superposed chambers. Sketch an external view and longitudinal
cross-section of Girtyocoelia (TSU IP 024) from the Pennsylvanian near Bridgeport, Texas.
Label spongocoel/cloaca, osculum and pore on the longitudinal section.
2. Class Hexactinellida
Those sponges with siliceous spicules, which have three axes arranged at mutual right angles
to form hexactines, are placed in the Class Hexactinellida. Members of this group are often
termed "glass sponges". Modern hexactinellids chiefly inhabit the upper bathyal zone, from 200
to 2000 meters water depth. Many species extend into the lower bathyal zone and members of
four modern families reach abyssal depths. Only one modern species is known from the hadal
zone, reaching depths of greater than 6000 meters. The range of hexactinellids is from Lower
Cambrian to Recent, although complete fossils are first recovered from rocks of Middle
Cambrian age.
EXERCISE # 18 - Sketch a lateral view of the cast of the hexactinellid sponge Hydnoceras
tuberosum, from the Upper Devonian of New York state (TSU IP 018).
3. Class Demospongia
Those sponges characterized by skeletons composed of spongin, or of spongin and siliceous
spicules, or of siliceous spicules which are built along symmetries other than that of
hexactinellids are included in the Class Demospongia. Demospongia have persisted as a major
class of sponges since inception of the record of the phylum in the Cambrian. The class includes
about 95% of all sponges in modern seas and all of the known freshwater forms. Demosponges
occupy environments that range from warm, shallow subtidal, high energy to quiet, cold oceanic
deeps. They range from exposed tide pool forms to cryptic (hidden) dwellers and include the
only boring sponges. Three genera of the Class Demospongea, Palaeomanon, Astylospongia and
Caryomanon, usually have their original shape preserved in the fossil state. These sponges are
subspherical or ovate, simple, and free with a rounded base showing no indication of having been
attached to the substrate. There is typically a very shallow depression on the upper surface into
which the excurrent canals emptied.
EXERCISE # 19 - Draw a top view of either Astylospongia (TSU IP 021) or Caryomanon (TSU
IP 022). Sketch an internal view of the polished section of Palaeomanon cratera (TSU IP 023)
and note (label) the straight radiating canals.
4. Class Sclerospongia
The Sclerospongia, the fourth class of sponges, have massive basal skeletons of calcium
carbonate that are overlain by a thin layer of living tissue that is, in turn, overlain by siliceous
opalline spicules. The Sclerospongia are the only poriferans in which mixtures of calcium
carbonate and silica occur in the skeleton and the three-layered aspect of their skeletal tissues
distinguishes them from all other sponges. The cell types of modern sclerosponges, their
organization, and what little is known of their development, indicate that sclerosponges are
related to demosponges. In modern environments, sclerosponges are typically inhabitants of
PALEO LAB # 2, PAGE 12
shaded crevices, caves and tunnels on coral reefs.
Stromatoporoids - For many years it was believed that stromatoporoids were hydrozoan
coelenterates. However, it now appears that they may belong to the Sclerospongia (although this
is still being debated). Although their classification is still somewhat of a puzzle,
stromatoporoids are not rare or small fossils. The Class Stromatoporoidea was abundant from
Ordovician through Devonian times. They are most often associated with fossil corals (Phylum
Cnidaria, Class Anthozoa) in reefs that are sometimes several hundred meters long and as thick
as 50 meters. In fact, they are the dominant reef-forming organisms in carbonate sediments of
Ordovician, Silurian and Devonian ages and made a strong come-back in late Mesozoic rocks
before succumbing in the Cretaceous Period. The structure of stromatoporoids consists of
horizontal elements, termed Lamellae or Laminae, and vertical partitions, termed Pillars. Thin,
overlapping, upwardly-convex plates are termed Dissepiments. Vertical elements, perpendicular
to the growth surface and forming in cross section a maze or labyrinthine network, are termed
Coenosteles. Short, thick elements parallel to the growth surface connecting coenosteles are
termed Coenostroms. The surface of stromatoporoids is smooth or raised into rounded
eminences, called Mamelons, and often bears radiating depressions in the surface (Astrorhizae)
that represents the stellate patterns of the exhalent canals leading to a central osculum.
EXERCISE # 20 - Examine a specimen of the stromatoporoid Actinostroma expansum with a
binocular microscope (TSU IP 020). Prepare a sketch of a portion of the polished surface. Label
the following features (if present): astrorhiza, mamelon, latilamina, pillar and lamina.
Chaetetids - The taxonomic classification of the chaetetids is uncertain. The genus Chaetetes
was originally regarded as a tabulate coral. However, most experts now believe the chaetetids
represent an odd group of sclerosponges, which range in age from the Ordovician through the
Tertiary.
The skeleton of chaetetids consists of clusters of calcareous tubes lacking septa; siliceous
monaxonal spicules are imbedded within the tube wall.
EXERCISE # 21 - Observe one of the hand specimens of Chaetetes milleporaceous (TSU IP
025, IP 027). Using a microscope, sketch a view of the thin section TSU IP 026 and label one of
the siliceous monaxonal spicules in your drawing.