Invertebrate Paleontology

TutorialWelcome to the Invertebrate Paleontology

Tutorial Web SiteThis web site was created to be a companion to the laboratory for GLY 363 - Invertebrate Paleontology. It is designed to provide the student

enrolled in GLY 363 with an additional resource for reviewing laboratory materials. It is set up in a format which parallels the

laboratory handouts. Most of the images contained within the web site are taken directly from specimens that are found on display for

study in the paleontology laboratory.

Topics

Taphonomy & Preservation

Protista, Eubacteria, & Porifera

Cnidaria

Bryozoa

Brachiopoda

Cephalopoda, Gastropoda & other Molluscs

Bivalve Molluscs

Echinodermata

Arthropoda

Miscellaneous Fossil Groups

Trace Fossils

Geologic Time Scale

Glossary

References

Links to other Paleontology Pages on the WWW

 

INTRODUCTION

As fossils are the preserved remains of ancient organisms or their traces, understanding the process of preservation, and more importantly, being able to

From Eldredge (1991)

recognize and identify fossil remains after their discovery is an integral part of paleobiology. Protective cover (sediments) and stabilizing chemical environments are of prime importance in the preservation of once living organisms. Due to the process of aerobic decay and physical/chemical destruction, most animals leave no evidence of their existence.

In order to make a correct interpretation of taphonomic processes and mode of preservation, it is often necessary to have a prior knowledge of the structural features or morphology of original skeleton in addition to knowing its original mineralogical composition. This limitation should diminish as you become familiar with the various fossil groups throughout the semester.

TAPHONOMY

Taphonomy is the study of what happens to an organism after its death and until its discovery as a fossil. This includes decomposition, post-mortem transport, burial, compaction, and other chemical, biologic, or physical activity which affects the remains of the organism. Being able to recognize taphonomic processes that have taken place can often lead to a better understanding of paleoenvironments and even life-history of the once-living organism.

In addition, understanding which taphonomic processes a fossil occurrence has undergone, and to what degree, may have implication on interpreting the significance of the fossil deposit and clearer understanding of the biases in the sample.

An outline of the pathways affecting the preservation of once living organisms can be found in Figure 1 below. As discussed below, this encompasses both the processes of biostratinomy and diagenesis.

Figure 1 - The field of Taphonomy as it relates to steps in transformation from living organisms to fossils.

Modified from McRoberts (1998)

Processes that occur between the death of an organism and its subsequent burial in the sediment are termed biostratinomy. Generally, this includes the decomposition and scavenging of the animal's soft parts, and at least some amount of post-mortem transport. Such things as the amount of shell breakage and the concentration of shells in layers often indicate the level of water energy and post-mortem transport. For example, the shell-hash or coquina   has experienced a significant amount of shell breakage and probably post-mortem transport suggesting deposition in high energy environments; whereas, the articulated plant remains   are intact suggesting little or no post-mortem transport and deposition in a very low energy and oxygen-free environment. InTable 1 below are various taphonomic indicators and their environmental implications.

The physical and/or chemical effects after burial are called diagenesis. This is the realm in which dissolution, replacement, or recrystallization of original shell material occurs, as can the formation of molds and casts. A more detailed description of diagenesis with regards to fossil preservation in the next section.

Table 1

Summary of Taphonomic Indicators and TheirPaleoenvironmental Implications

TAPHONOMIIMPLICATIONS

C FEATURE

Abrasion

The wearing-down of skeletons owing to differential movement with respect to sediments is an indicator of environmental energy. Significant abrasion is most commonly found on skeletal material collected from beaches, or areas of strong currents or wave action.

Articulation

Multi-element skeletons are soon disarticulated after death. Articulated skeletons, then, indicate rapid burial or otherwise removing the skeleton from the effects of energy of the original environment.

Bioerosion

Bioerosion encompasses the many different corrosive processes by organisms. The most pervasive causes of degradation are boring and grazing. Bioerosion erases information from the fossil record, but it also leaves identifiable traces made by organisms on remaining hard skeletons or surfaces. Therefore, trace fossils produced by bioerosion add information on the diversity of ancient assemblages.

Dissolution

Skeletal remains commonly are in equilibrium with surrounding waters, but changes in chemical conditions can cause skeletons to dissolve. Dissolution represents fluctuation in temperature, pH or pCO2 in calcium carbonate skeletons. Siliceous skeletons also can dissolve because normal sea water is usually undersaturated with respect to silica.

Rounding

Broken edges of skeletons become rounded owing to dissolution and/or abrasion of exposed surfaces. Processes that control edge rounding probably include a combination of dissolution, abrasion, and bioerosion. Rounding gives an estimate of time since breakage.

Encrustation

The growth of hard skeleton substrates by other organisms is a common occurrence. Besides indicating exposure of the skeleton above the sediment-water interface, encrustation can specify a particular environment. Different patterns of encrustation, as well as different biota, occur in different environments.

Fragmentation

Breakage of skeletons is usually an indication of high energy resulting from wave action or current energy. Fragmentation also

can be caused by other organisms through either predation or scavenging.

Orientation

After death, skeletal remains are moved by the transporting medium and oriented relative to their hydrodynamic properties. Fossil skeletons in life position indicate rapid burial, attachment to a firm substrate, or death of in-place infauna. Hard parts tend to orient long-axis parallel to unidirectional flow in current-dominated areas and perpendicular to wave crests on wave-dominated bottoms.

Size

After death and if not rapidly buried, a skeleton behaves as a sedimentary particle and is moved and sorted with respect to the carrying capacity of the flow of currents, waves, or tides. Size can, therefore, be an effective indicator of flow capacity in a hydraulic or wind-driven system.

From McRoberts (1998)

 

TAPHONOMY & PRESERVATION

FORMS OF PRESERVATION

UNALTERED

This form of preservation is rare in most of the geologic column, but becomes more frequent in younger sedimentary rocks. Types of unaltered preservation where even the soft body parts are preserved include: (i) mummification, (ii) encasement in tar, (iii) encasement in amber, (iv) encasement in sediment, and (v) freezing. More frequently, however, only the hard skeletal material is preserved after removal of soft body parts.

Examples of unaltered preservation include the skeleton of a horseshoe crab,   whose

shell is composed of interlocking plates and jointed appendages which quickly disarticulate after death; cockle bivalved molluscs,   whose outer-most shell layer has been removed by abrasion, yet the original shell material of the inner layers remains; an ammonoid   from the Cretaceous period in which you should note the pearly luster which is original aragonite shell material; and an insect encased in amber  .

MOLDS & CASTS

This general class of preservation entails making "replicas" of the skeletal hard parts of organisms. In general, a mold is an impression in the sediment of a skeleton or shell. Once encased in lithified sediment, the dissolution of skeletal material leaves behind the impression or mold of original skeletal form. Thus, a mold is a "mirror image" of the original skeleton. An internal mold (sometimes called a steinkern) is the impression of the inside surface of skeletal hard parts. An external mold is the impression of the outside surface of skeleton or bone. An example of both types of molds can be seen in this image of a trilobite  .

A cast is formed by the filling-in of a mold. It is thus a true replica (not a "mirror image") of the original skeleton or shell. By this definition, the cast one gets for a broken limb is not really a cast at all but an external mold.

A graphical representation of the formation of casts and molds is provided in Figure 2 below.

Figure 2 - Different diagenetic processes leading to different preservational styles in skeletal materials.

* Note that molds are produced directly as imprints of the shell and casts are produced from molds.

Modified from McRoberts (1998)

REPLACEMENT & RECRYSTALLIZATION

This common form of preservation involves chemical and/or physical alteration or replacement of original skeletal material. To properly identify replacement and recrystallization, one must know what the original constituents of the organism's skeleton were. These are provided in Figure 1.3. Replacement occurs often by the filling in (by various minerals) of the void space after dissolution of original skeletal material. Sometimes, the replacement occurs on a molecule by molecule basis. Common replacement minerals that you should be able to recognize include Silica (SiO2) as shown in the coral,   and Pyrite (FeS2) shown in the ammonoid. 

Recrystallization involves the physical re-arrangement of crystalline structure of skeletal material. This is a common phenomenon in shells which were originally aragonite and/or calcite (both forms of calcium carbonate- CaCO3). Examples, both of which are now calcite, include a gastropod which was originally aragonite and a brachiopod which was originally calcite. 

CARBONIZATION

As organic remains decompose in sediments, volatile constituents such as oxygen, hydrogen, and nitrogen are slowly lost to the surrounding sediments frequently leaving behind a carbon film. This process is carbonization (or sometimes called distillation), and occurs most frequently in oxygen deficient, organic-rich environments such as basinal black shales, and coal swamps. The carbon films often show exquisite details of plants and soft-body parts of animals not readily preserved, and can often be recognized by a dark gray or black film with a metallic sheen such as these fern-like fossil plants. 

PERMINERALIZATION

Permineralization involves the filling-in of pore and/or void spaces in shell or bone by secondary mineral matter in solution. With permineralization, the tiny pore spaces in the fossil are filled and the original skeletal material is still retained. However, it is often common for other types of preservation (e.g. replacement) to occur during and/or after permineralization. Because of its porous nature, bone and wood   is especially prone to permineralization.

PROTISTA, EUBACTERIA, & PORIFERA

From Stanley (1993)

Kingdoms EUBACTERIA and PROTISTA

Fossil organisms within the Kingdom Protista represent the earliest life forms known. These organisms are characterized by a single-celled body plan and are contrasted to members of the Kingdom Eubacteria (green and blue-green algae) by having a nucleus. This lab concentrates on the protist phylaForaminifera and Diatoms because many of their constituents have mineralized skeletons and an extensive fossil record. Because of their wide-spread distribution and rapid evolutionary rates, many of the protists are excellent index fossils used in biostratigraphic studies. During this lab you will become familiar with the morphologic features and be able to identify each of the groups listed below, in addition to knowing their geologic ages.

The recepatulitids are included here because they are now believed to belong to the Chlorophyta or green algae within the simply organized Kingdom Eubacteria even though they were once thought to be related to sponges.

CLASSIFICATION & GEOLOGIC RANGES

Kingdom Eubacteria (Precambrian - Recent)

group "stromatolites" (Archaen - Recent)

Kingdom Protista (Precambrian - Recent)

group "receptaculitids" (Ordovician - Devonian)  Phylum Granuloreticulosa

Class Foraminifera (Cambrian - Recent)      group "fusulinids"(Late Paleozoic)

group "nummulitids"(Early Cenozoic)      "planktonic forams" ( Cretaceous-Rec.)

Phylum Acrtinopoda

Class Radiolaria (Cambrian - Recent)

Phylum Chrysophyta

"diatoms" (Cretaceous - Recent) 

Kingdom Eubacteria

"Stromatolites"

Stromatolites are organically produced sedimentary structures and are amongst the oldest fossils known on Earth (they occur in Archean rocks 3.5 b.y. old!). they are made by cyanobacteria (often erroneously called “blue-green algae”, however, because the cells are prokaryotic, they should not be confused with true algae which are eukaryotes. Stomatolites are without skeletons (they are layers of sediment), and differ from some similar-looking sponges that have a mineralized skelton.

Kingdom Protista

"Receptaculitids"

Receptaculitids are a type of Dasycladacean green algae (Phylum Chlorophyta). They are characterized by thick calcareous sheets, plates, or sometimes as balls or discs that are perforated by numerous holes arranged in an orderly (usually spiral) fashion.   The holes are in fact external molds of the plant's soft stems and not body fossils at all.

Class FORAMINIFERA

Foraminifera are the most common and geologically most important of the fossil protozoans. The name translates to pore-bearing and refers to the numerous perforations (foramina) in the skeleton walls. It is through the foramina that the organism extends its pseudopod or protoplasm.

Today, nearly all forams live in marine environments and are either bottom dwellers (benthonic) or float in the water column (planktic). Forams are characterized by multi-chambered tests which are built by addition of new chambers during life. Chambers are separated by partitions called septa (singular = septum), whose exterior expressions are termed sutures. Composition of the tests are either calcite (CaCO3) or agglutinated (cemented foreign particles, e.g., sand or silt grains).

The classification of Foraminifera is based on (i) test microstructure, (ii) test symmetry, and (iii) aperture type.

Test Composition and Microstructure

Agglutinated (sometimes called arenaceous). These tests are composed of grains or fragments of foreign material cemented by the organism and commonly have a sugary appearance.   Occasionally grains of quartz and/or shell fragments can be seen.

Calcareous tests can either be hyaline which can be distinguished by their glassy appearance   or porcelainous which are usually white or opaque in color and resembles china or porcelain. 

Test symmetry

1. Uniserial. Chambers are added in a straight or curvilinear series. (see Figure 1 below)

2. Biserial. Chambers are added in an alternating fashion.

3. Triserial. Chambers are added every 120o in a spiral fashion.

4. Planispiral. Chambers are added around the periphery and are coiled in a single plane. Planispiral tests are evolute when all previous chambers are visible, and are involute when only the last spiral or whorl is visible.

5. Trochospiral. Chambers are added around the periphery, but each new chamber is slightly offset so that a very low spire or cone results. The central part of the disc on the side of the aperture is called the umbilicus.

Figure 1 - Foraminifera Test Morphology

From Boardman et al (1987)

Ecology

During life, forams are either benthonic of planktic, relying on their pseudopodia for both locomotion and creating water currents for food gathering.

Benthic forms inhabiting shallow to deep water environments can be recognized by their larger size, thick heavily ornamented walls, and less "globular" shape. 

Planktic forams are recognized by their thin, and often perforated, tests and globular inflated chambers.   You should be able to recognize the difference between the two types of forams.

Larger Foraminifera

Several times during the history of Foraminifera, tests many times larger than you have been seen until now have evolved. Although large tests are known from several foraminiferal families, only two, the fusulinids (Family Fusulinidae) and nummulitids (Family Nummulitidae) are considered below.

The nummulitids existed during the Early Cenozoic and are famous for their abundance in limestones from which the Great Pyramids of Egypt built. Their tests are planispiral and involute, and unlike the fusulinids, are coiled around the short axis. Examine this specimen from Egypt. 

The fusulinids were important benthic constituents of Late Paleozoic shallow seas. The tests of fusulinids are involute and planispirally coiled about the long axis. The test walls of fusulinids are multi-layered in contrast to the microgranular tests of other forams. An individual fusulinid can be seen in this image.   A good example of a fusulinid limestone can be seen in this image. 

RADIOLARIA

Radiolarians are heterotroph protozoans which thrive in the upper layers of the seas. The protoplasm of radiolarians is surrounded by a test commonly composed of an intricate lattice work of opaline silica (there are minor groups which construct their tests of strontium sulfate a silica enriched with organic material). Like the foraminifera, radiolarians have pseudopodia which protrude through the porous tests to aid in locomotion and food gathering. The tests of radiolarians exhibit great morphologic diversity, but they are typically characterized by radial or spherical symmetry. Examine this microscope image.

Phylum CHRYSOPHYTA

"Diatoms"

Diatoms are a kind of microscopic golden-brown algae that secrete siliceous tests (sometimes called frustules) consisting of two overlapping halves or valves that fit together. The walls of the tests are ornamented by pores, grooves, and ridges.

Diatoms occur in two basic forms: (i) the centric type in which the test has radial symmetry, and (ii) the pennate type in which the test is elongate and has bilateral symmetry. An example of both types can be seen in this microscope image. 

The centric type are planktic and predominantly marine, whereas the pennate type are mostly benthic and occur in fresh, brackish, and shallow marine environments. Sometimes diatoms form a rock called diatomite, which is composed entirely of diatoms. Diatomite often forms by a diatom "bloom" in nutrient-rich fresh-water lakes.

 

PROTOCISTA, EUBACTERIA, & PORIFERA

PORIFERA & ARCHAEOCYATHA

Sponges, stromatoporoids, and archaeocyathids are included in this part because individual members within each group share, at least partially, similar skeletal features and symmetry leading some workers consider them all as being members of the same phylum. All are benthic, sessile, suspension-feeders which inhabited a wide variety of exclusively marine environments throughout much of the Phanerozoic.

CLASSIFICATION & GEOLOGIC RANGES

Phylum Porifera

Class Demospongea (Cambrian - Recent

Class Hexactinellida (Cambrian - Recent)

Class Calcarea (Cambrian - Recent)

"Class Stromatoporoida" (Ordovician - ?Recent)

Phylum Archaeocyatha (Cambrian)

 

Phylum PORIFERA

Figure 2 - Basic Sponge Morphology

From Boardman et al (1987)

The poriferans (sponges) are characterized by cell groups that are independent of each other and have the ability to change their function during their life cycle. The skeletons of sponges can be composed of an organic substance called spongin (the stuff of an ordinary bath sponge), or they may have calcareous or siliceous skeletons composed of chambers, or more commonly rod-like branched elements called spicules. After death, spicules are scattered across the sea floor and may be found as disarticulated microfossils. 

Large spicules (visible to the unaided eye) are termed megalascleres, whereas small ones are called microscleres. Spicules have four basic symmetries: (i) monaxon, (ii) triaxon, (iii) tetraxon, and (iv) polyaxon. Examine Figure 2 below. Together the spicular symmetry and mineral composition serve as the primary basis in poriferan classification.

Figure 2 - Nomenclature of Common Megascleres & Microscleres in Fossil and Modern Sponges

Modified from Boardman et al (1987)

Class Demospongea

Sponges with skeletons of spongin, spongin and siliceous spicules, or a skeleton of fused opaline silica. When present, spicules are commonly monaxon, tetraxon, or polyaxon, but never triaxon. Here is an example of a modern demosponge with spongin.   Here is a good example of a fossil demosponge.  Note in this specimen the canals in the siliceous walls.

Class Hexactinellida (previously Hyalospongae)

Sponges with siliceous spicules that are usually triaxons and commonly fused to form a net or box-like pattern. They are often called glass sponges. For a recent example of a glass sponge, view this image.   Compare it with Hydnoceras   from the Devonian of New York.

Class Calcarea

Sponges that have calcareous spicules as in Astaeospongia (the disc shaped fossil in the following image) or more commonly, non-spicular porous chambers (the other three fossils in the image). When spicules are present, they are not fused and are typically monaxons and/or tetraxons. 

"Class Stromatoporoida"

Although some texts treats this group as a member of the demospongea, some paleontologists consider stromatoporoids not as true sponges, but belonging to their own phylum. The middle road is taken in this course, treating the stromatoperoids as a separate class within the Porifera. The sheet-like or hemispherical skeletons of stromatoporoids are of two types. The first type have small mounds called mamelons from which canals called astorhizae radiate.   This group has horizontal partitions called laminae and vertical partitions called pillars. The space between the laminae and pillars is called the gallery. Compare the image with the accompanying figure below.

Figure 3 - Stromatoporoid Morphology

From Boardman et al (1987)

The second type of stromatoporoid is similar to the first in having laminae and possibly pillars, yet it lacks the astorhizae and mamelons. This form is quite similar to algal stromatolites, but differ in possessing a true calcareous skeleton. Stromatoporoids such as these   are quite common from the Silurian and Devonian shallow-water carbonates of central New York and also the Canadian Rockies where they often built reefs.

Phylum ARCHAEOCYATHA

The Archaeocyathids are predominantly an Early Cambrian phylum with no living representatives. They generally have skeletons that formed a porous calcareous cup or cone that resembles later Paleozoic corals. In fact, the archaeocyathids where the reef builders of the Early-Middle Cambrian. The cone-shaped skeletons are commonly constructed of two perforate walls separated by radially arranged vertical blades called septa. As shown in the accompanying figure, the skeletons of archaeocyathids come in two varieties: (i) regulars that have both septa and tabulae but lack dissepiments (small curved plates), and (ii) irregulars that lack septa, but have dissepiments and rod-like bars similar to sponge spicules. This similarity has led some to believe that archaeocyathids belong with the Phylum Porifera. See the diagram below for a

representation of an archaeocyathid.

Figure 4 - Archaeocyathid Morphology

From Boardman et al (1987)

CNIDARIANS

From Eldredge (1991) 

INTRODUCTION

The phylum Cnidaria (Coelenterata in some texts) includes both solitary and colonial organisms that have radial and/or bilateral symmetry. Typical cnidarians alternate each generation between a fixed polyp stage and a free living medusoid stage. Most cnidarians are considered carnivores because of their ability to actually catch food with their stinging cells called nematocysts. Some groups, particularly the reef-corals employ photosynthetic algae (zooxanthellae) within their tissues in a symbiotic relationship to aid in supplying food needed for their rapid growth.

The cnidarian classes Anthozoa (corals) and Hydrozoa have calcified skeletons of aragonite and calcite and a good fossil record, whereas the long fossil record of the class Scyphozoa (jelly fish) is comprised mostly of molds and casts. Class Octocorallia is not well represented in the fossil record because of its poorly calcified skeletons. The general form of coral colonies may be quite similar in unrelated anthozoans (e.g., some colonial Tabulates and Scleractinians) because form represents a basic response to long-term environmental conditions (i.e., limiting factors such as light, turbidity, and especially wave and current energy).

The first part of the lab introduces you to the taxonomy of the Cnidarians and their

geologic ranges. The second part concentrates on aspects of coral morphology, coloniality, and integration that are used to deduce ancient environments

CLASSIFICATION & GEOLOGIC RANGES

Phylum Cnidaria

Class Anthozoa (Precambrian-Recent)

Order Tabulata (Ordovician-Permian)

Order Rugosa (Ordovician-Permian)

Order Scleractinia (Triassic-Recent)

Subclass Octocorallia (Precambrian-Recent)

Class Hydrozoa (Precambrian-Recent)

Class Scyphozoa (Precambrian-Recent)

 

Class ANTHOZOA

Geologically the anthozoans are the most important of the cnidarians because their polyps often produce calcitized skeletons that are readily preserved as fossils. They can be either solitary or colonial. Common forms of anthozoans include corals, sea-anemones, and sea-pens. Anthozoans differ from other Cnidaria in that they have no medusoid stage. They are exclusively marine and occur at various depths from shallow to deep water.

Morphologic Terms (see accompanying figures)

Calyx: the bowl-shaped depression or "seat" in which the living polyp resides.

Corallite: the skeleton produced by one polyp, which may or may not be part of a colony

Epitheca: the outermost skeletal layer of a corallite which sometimes shows growth lines.

Tabula (plural tabulae): a horizontal partition (or floor) dividing the corallite skeleton.

Septum (plural septa): vertical blade or partition within the calyx of a corallite that are normally radially arranged.

Dissepiment: small curved plate in a corallite near the tabulae that is convex inward and upwards.

Mural pores: the small holes in the epitheca of some tabulate corals.

Columella: an axial rod in a corallite usually formed by the fusion of two or more septa that typically forms a topographic prominence in the central part of the calyx.

Order TABULATA

The exclusively colonial Tabulate corals occur only in the Paleozoic. Their calcite skeletons typically have a lateral wall (epitheca) that separates each rather small corallite. Each of the corallites typically have a tabula that serve as the floor for the polyp. Septa in tabulate corals are either absent or inconspicuous. Although their growth forms vary, they often occur in "honeycomb" or chain-like morphologies.

Figure 1 - Tabulate Morphology

From McRoberts (1998)

See examples: Favosites which has well developed tabula,  and  which has well developed mural pores; and Haylisites. 

Order RUGOSA

Figure 2 - Rugosan Morphology

From McRoberts (1998)

The Paleozoic rugosan corals can be either solitary or colonial. Although they may have originally had aragonitic skeletons, all are now calcite. Rugosa corals are distinguished from the other Paleozoic group, the Tabulata, by having dissepiments and well developed septa in addition to the tabulae. As shown in the accompanying figure (Figure 3.1), rugosan corals have six primary septa and new septa are added in only four of the resulting six spaces with none added in the remaining two spaces. This septal arrangement is well illustrated in the external mold   where the septa are preserved as gaps.

For examples of solitary forms which typically exhibit a cone or horn morphology (hence the informal name "horn corals") examine these specimens,   -  and   This specimen has excellent dissepiments visible where the epitheca is worn-away.   For examples of colonial rugosans view this specimen. 

Figure 3 - Septal Growth Patterns

Modified from McRoberts (1998)

Order SCLERACTINIA

Scleractinian corals (including all modern coral species) can be either colonial or solitary. Their originally aragonitic skeletons have dissepiments, tabulae, and septa just as in the Paleozoic rugosans. Although there are superficial similarities, scleractinian corals differ from rugosa corals by their skeletal mineralogy and by their method of septal insertion during growth. Scleractinian corals also have six primary septa, but in contrast to rugosa corals, subsequent septa are added in all six of the resulting spaces. An important distinction between the two orders is that for the Scleractinia the septa are inserted between every two pre-existing septa in later growth stages. Good examples showing corallites and septal arrangement in a colonial form can be seen in this specimen.   See also the colonial specimens,   -   -   -  noting the different growth morphologies. This specimen is a solitary coral collected from deep water; note its similarity to some of the solitary rugosans seen earlier. 

Subclass OCTOCORALLIA

Although octocorals are very abundant in modern oceans, they do not have a good fossil record at all because of their lightly calcitized skeletons. Among the more

common octocorals are sea whips and sea fans such as shown by these specimens.   -   -   Other groups of octocorals have even a poorer fossil record because they have only calcitic spicules or non-calcified skeletons. One of the latter group are the sea-pens which have soft, feather-like skeletons.

Class HYDROZOA

Hydrozoans are a diverse group of cnidarians that inhabit a variety of marine and fresh-water environments. The more important groups (in terms of paleontology) construct their skeletons of calcite. These critters can sometimes superficially resemble corals in skeletal morphology and growth habits, or they can also occur as encrusting sheets or erect blades. Some hydrozoa such as the fire coral Millipora have thick calcareous lamellar skeletons with vertical tubes and cross partitions. 

Class SCYPHOZOA

Scyphozoa (jelly fish) only occur in marine environments. The are typified by a reduced polyp stage and an extended free-swimming medusae stage. As one might imagine, fossil scyphozoans are rarely preserved as fossils; yet surprisingly they are probably represented in the famous Ediacara fauna of the Precambrian. Almost all fossil remains of scyphozoans occur as molds and less commonly casts. Some workers would place the Conularia as a Subclass of the Scyphozoa.

CNIDARIANS

PALEOECOLOGY

 

Colonial coral growth habits and integration levels

The morphology of coral colonies can be grouped into three broad categories: (i) encrusting forms which are often sheet-like such as this specimen.   (ii) massive forms which are domal or hemispherical such as in specimen.   (iii) erect forms which are branching or palmate such as this specimen   You should return to the coral specimens in the first part of the lab making sure you can place each into one of the three morphologic groups.

Colonial corals nearly always show some level of integration between individual coralites. Such integration is usually reflected in the coral's skeleton by the degree of spetal sharing ranging from completely isolated corallites to those where individual corallite cannot be recognized.

Figure 4 - Colonial Cnidarian Integration Types

From McRoberts (1998)

You should return to the specimens of the earlier part of the lab and make sure you can identify the integration types depicted in Figure above. You should find, for example, that this specimen,  is cateniform, this specimen,   is cerioid, and this specimen,   is meanderoid.

It is important to know that different integration levels were dominant during different periods of geologic time. In fact, given a large enough sample, a rough estimate of gelogic age can be obtained on the relative proportions of various integration levels.

Paleoenvironments

Corals occur as framework organisms in reef environments and as important constituents in level-bottom communities. As a group they are very sensitive to physical and chemical conditions such as fluctuating sea level, turbidity, and salinity. Of all of these factors which may result in differing growth morphology, the overall shape of coral colonies is most responsive to water (= wave + current) energy. However, it should be noted that the morphologic response is quite different when a coral is in a reef setting or in a level bottom setting.

From McRoberts (1998)

Although quite diverse in large-scale morphology and facies relations, reef systems generally conform to the scheme depicted in the accompanying figure . Note that the reef proper (the organic build-up) is quite restricted in size compared to the reef system as a whole. In reef settings, the degree of branching in colonial corals can generally be correlated with water energy. Thus high energy often results in erect, branching and palmate forms, whereas lower water energy levels are generally sites where the encrusting and/or massive forms predominate.

The opposite is generally true for level-bottom settings such as is often found in the Devonian of central New York. Here, greater water energy usually results in encrusting and/or massive morphologies. This is in contrast to lower water energy level bottom environments where branching and ramose morphologies (albeit more delicate than in reefs) predominate.

BRYOZOAN

S

From Eldredge (1991)

INTRODUCTION

The Bryozoa (moss animals) are a geologically important group of small animals; some that superficially resemble corals. All bryozoans are colonial and most are marine. Bryozoans are most abundant in temperate-tropical waters that are not too turbid. They require a hard or firm substrate on to which the attach to or encrust, and clear agitated water from which they obtain their suspended food.

Enclosed within a skeleton of calcite, bryozoans have a sac-like coelomate body with a well defined mouth, anus, and other specialized organs. One such organ is the lophophore (a ciliated structure used in food gathering) that is attached to tentacles that surround the mouth (see Figure 1 below). The lophophore is a structure shared by the phylum Brachiopoda leading some to construct the Phylum (or Superphylum) Lophophorata to include both brachiopods and bryozoans. The classification follows your text in treating the Bryozoa and Brachiopoda as separate phyla.

Figure 1 - Section of a Bryozoan Feeding Zooid

From Boardman et al (1987)

CLASSIFICATION AND GEOLOGIC RANGES

Phylum Bryozoa

Class Stenolaemata (Ordovician-Recent)

Order Trepostomata (Ordovician-Triassic)

Order Fenestrata (Ordovician-Permian)

Order Cyclostomata (Ordovician-Recent)

Class Gymnolaemata (Ordovician-Recent)

Order Cheilostomata (Jurassic-Recent)

 

GENERAL MORPHOLOGY AND ECOLOGY

Morphologic Terms (see Figures 1 & 2)

Zooid: Individual animal or member in a bryozoan colony.

Zooaria: The colony of bryozoan animals.

Zooecia (Zooecium singular): Living chambers constructed by a colony of zooids. The zooecium is the living chamber constructed by one individual.

Autopore: Zooecium for the feeding zooid called autozooid which is usually the largest of the various zooecia.

Ancestrula: The ancestral founding zooecium from which other zooecia in the colony bud.

Diaphragm: A partition in a tubular zooecium, transverse to tube length similar to the tabulae in some corals.

Aperture: The opening through which the living animal could extend from its zooecium.

Operculum: Small disk-like cover or lid of an aperture, commonly found in cheilostomes.

Frontal: In zooecia with considerable wall area exposed at the colony surface, a frontal is the exposed part of any one zooecium.

Immature and Mature regions: In trepostome bryozoans, the distal or last formed (most recently grown) end of a zooecium has close-spaced diaphragms and is called the immature area. The proximal end (oldest part) of the zooecium has few diaphragms and is called the mature region.

Figure 2 - Section of a Colonial Bryozoan Zooecia

From Boardman et al (1987)

General Morphology and Ecology

As bryozoan individuals are quite small, they are commonly observed under the microscope from longitudinal or transverse thin-sections. A longitudinal orientation is parallel to zooecium wall, whereas a transverse section is perpendicular to apertural face.

Bryozoans come in a variety of colonial growth habits that can easily be observed without thin-sections. Like corals, the growth habit of bryozoans can be classified as encrusting,   -   massive or domal,   or erect.   -   Generally speaking, byozoan growth-habits are a function of water energy similar to corals which lived in level-bottom communities; encrusting and massive forms are found in high-energy environments whereas delicate branching and erect forms lived in quite environments.

BRYOZOANS

CLASSIFICATION

General Information

Division of bryozoan groups is based on surficial morphology, extra-zooidal structures, colonial growth habits, zooid morphology, presence of specialized zooids (e.g., maternal zooids), and internal structures of the zooecium. In order to help in identification, it may help to know that colonial bryozoans come in two basic types:

1. Those with tightly packed zooecia which share zooecium walls, they have multiple

pores and a well defined mature and immature region such as in the trepostomes, cyclostomes, and the fenestrates.

2. Those with moderately to loosely packed zooecia usually encrusting one-zooecium-thick, and commonly with frontal walls as typified by the Cheilostomes

 

CLASSIFICATION AND GEOLOGIC RANGES

Phylum Bryozoa

Class Stenolaemata (Ordovician-Recent)

Order Trepostomata (Ordovician-Triassic)

Order Fenestrata (Ordovician-Permian)

Order Cyclostomata (Ordovician-Recent)

Class Gymnolaemata (Ordovician-Recent)

Order Cheilostomata (Jurassic-Recent)

Order TREPOSTOMATA

Trepostomes are characterized by long-curved zooecia separated by thin walls. Each zooecium has mature and immature regions. Apertures of autopores are typically

polygonal. Trepostomes can be differentiated from similar-looking cryptostomes by the thinner walls between their zooecia. The specimens are erect forms,   whereas these specimens are massive. 

Order CYCLOSTOMATA

Cyclostomes are characterized by zooecia that are simple tubes which lack partitions (diaphragms) and have rounded apertures. and well defined mature and immature regions. Most cyclostomes are encrusting forms such as the example provided.  , and some, like this small figured specimen   encrusting a Devonian nautiloid cephalopod, can be quite small and very loosly arranged creeping zooecia.

Order FENESTRATA

Fenestrates are characterized by their zooaria morphology which form a mesh or net-like shape with zooecia-bearing rods and open window-like regions called fenstrules. Most fenestrates have considerable extra-zooid skeleton material which is necessary for support. This order is typified by erect, delicate morphology such as those seen in these specimens.   Note, however, that some fenestrates have considerable extra-zooidal material such Archimedes which is an axial rod that supports the net-like zooecia. 

Order CHEILOSTOMATA

Cheilostomes are characterized by their loosely packed colonies of box or coffin-shaped zooecium. Many have round apertures and large frontal areas on which brood pouches which house the maternal zooids can often be observed.  .

CEPHALOPODA, GASTROPODA

& other Molluscs

 

From Eldredge (1991)

 

INTRODUCTION

Molluscs are greatly varied in both morphology and life habits. They include familiar living forms such as clams, snails, the octopus, and squids. Several groups have great economic importance such as oysters and the blue mussels, and some groups such as

garden slugs and the zebra mussel can be bothersome pests. In this laboratory you will become familiar with several of the molluscan groups, of which the cephalopods and gastropods are geologically the most important.

Most molluscs are mobile marine creatures, although some have invaded terrestrial environments. Molluscs have an external shell (single or bivalved) enclosing the mantle and visceral mass, a muscular foot which aids in attachment and/or locomotion, and a radula. The radula is not known from the bivalves (a group covered in the next lab), but is presumed to have been primitive in the bivalve ancestor.

CLASSIFICATION & GEOLOGIC RANGES

Phylum Mollusca (Precambrian-Recent)

Class Monoplacophora (Cambrian-Recent)

Class Amphineura (U. Cambrian-Recent)

Class Schaphopoda (Ordovician-Recent)

Class Gastropoda (Cambrian-Recent)

Subclass Prosobranchia (Cambrian-Recent)

Order Archaeogastropoda (Cambrian-Recent)

Order Mesogastropoda (Ordovician-Recent)

Order Neogastropoda (Cretaceous-Recent)

Subclass Opisthobranchia (Carboniferous-Recent)

Subclass Pulmonata (Carboniferous-Recent)

Class Cephalopoda (Cambrian-Recent)

Subclass Coleoidea (Devonian-Recent)

Subclass Nautiloidea (Cambrian-Recent)

Subclass Ammonoidea (Devonian-Cretaceous)

 

Class MONOPLACOPHORA

The organ system of monoplacophorans are arranged in a series and are segmented (or pseudosegmented) leaving paired muscle scars on the shell interior. Some investigators suggest that a Paleozoic and early Mesozoic group called the Some fossils typically classed as bellerophons (here treated as gastropods), may have an untorted body plan. This has been deduced from the arrangement of muscle scars on the interior of the univalve bellerophons. Most other bellerophons, however, do exhibit torsion and should rightly be classified as true gastropods. Apart from the bellerophons (no muscle scars can be observed in our specimens) we have no monoplacophoran specimens.

Class AMPHINEURA

Amphineura (Polyplacophora of some texts and commonly referred to as the Chitons) are characterized by an elongated body with a head and bilateral symmetry. Polyplacophorans possess a radula. The soft bodies of polyplacophorans are surrounded by a muscular mantle girdle (cuticle) which has aragonitic spicules. Above the mantle cuticle, polyplacophorans have a dorsal shell made up of eight articulated plates or valves. Some recent examples of polyplacophorans are provided here. 

Class SCHAPHOPODA

Scaphopods (commonly called tusk shells for obvious reasons) are a relatively minor class of marine molluscs. They can actively trap food particles within the sediment by use of their specialized tentacles. Scaphopods are characterized by a small univalved

shell that is open at both ends. The larger anterior end is permanently embedded in the sediment. The smaller posterior end is opens near the sediment-water interface. See the examples of Recent and fossil Dentalium. 

GASTROPODS

CLASSIFICATION & GEOLOGIC RANGES

 

Phylum Mollusca (Precambrian-Recent)

Class Gastropoda (Cambrian-Recent)

Subclass Prosobranchia (Cambrian-Recent)

Order Archaeogastropoda (Cambrian-Recent)

Order Mesogastropoda (Ordovician-Recent)

Order Neogastropoda (Cretaceous-Recent)

Subclass Opisthobranchia (Carboniferous-Recent)

Subclass Pulmonata (Carboniferous-Recent)

 

Class GASTROPODA

Gastropods, including such common forms such as snails, slugs, and whelks, occupy both marine and non-marine environments. Although many gastropods are herbivorous grazers, several groups are active carnivores able to drill through the skeleton of the luckless victim.

Most of the gastropods are classified on the characteristics the gill structures and other soft-bodied features. Few distinguishing characters of the univalved shell are used in classification as many are the result of convergent evolution. Although the differences in the shell form may be difficult to recognize, different morphologic groups can generally can be differentiated on characteristics of ornamentation, shell shape, and aperture. The shell of many gastropods can either be external   or, less commonly, internal.   The difference can often be deduced by the luster of shell material and the presence of other features such as deviations of a structural shell form.

Gastropods are radulate organisms with a torted body (e.g., the body is rotated 180û so that the anus is above the head. Gastropods typically have a helical coiled univalved shell whose opening (aperture) may be closed by an operculum.   Another feature which is useful in discriminating among groups is the structure called the selenizone which can be expressed as either a series of holes as in Haliotis,   or as a groove along the periphery which is often seen as a sharp bend in the growth lines of the shell.   Other features such as ribs or the siphonal canal may also be important.

Although the shape of gastropods can be described in terms such as "high-spired", "low-spired", or "cap-shaped", many of the shape characteristics can easily be described mathematically by four parameters S, W, T, and D.

Figure 1 - Gastropod Coiling Parameters

Where:

S shape of generating curve (loosely defined as the ratio between aperature height and width)

D distance of generating curve from the axis of rotation

W rate of expansion of generating curve

T rate of translation along the coiling axis

Modified from McRoberts (1998)

Subclass Prosbranchia

The distinguishing shell feature among prosobranch gastropods is that they are all either cap-shaped or they are helically coiled.

Order Archaeogastropoda. Many archaeogastropods have an identifiable selenizone (except for some trochids) in addition to an operculum. The shell of archaeogastropods can be either internal or external. This group is exclusively marine. Most are turbinoform,   but others may be high spired,   cap-like as in recent limpets,   or other shapes. Many of the cap-like archaeogastropods have a small hole in the apex of the cap which is a modified selenizone. The selenizone of other species of

archaeogastropods may be a series of holes such as in Haliotis.   As mentioned earlier, the group of involute univalves with a selenizone called bellerophons, (especially those with unpaired muscle scars), may be regarded as Archaeogastropods. Examples of bellerophons are provided. 

Order Mesogastropoda Mesogastropods do not have a selenizone. Their shell can be either internal,   which commonly have a slit like aperture, or external,   in which round or ovid apertures are common, some of which have a lip. A very common group includes the turritellids,   a high-spired group typical of post-Jurassic. Another common example of mesogastropods are the slipper shells,   belonging to the genus Crepidula. Other forms, such as the filter feeder Vermicularia,   often become uncoiled (or vary coiling parameters) during ontogeny. Of special note is the common low spired Polynices, who is an active carnivore who drilled holes in the shells of other molluscs. 

Order Neogastropoda Neogastropods do not posses a selenizone, yet they typically have a siphonal notch or canal and elongated and non-circular, and commonly slit-like, apertures. Typical examples of this group occur in the common whelks and others with strong ornamentation.   -   Although other forms such as Conus are also quite common.

Subclass Pulmonata

Pulmonates can have an external or internal shell, or the shell may be absent (e.g. terrestrial slugs). Many pulmonates are terrestrial or live in lacustrine environments. The pulmonates can typically be recognized by their often thin shells and distinct shell morphology which is typically conispiral and rather bulbous. Furthermore, many pulmonates have a well defined aperture lip as in Helix.   Here are several other examples. 

Subclass Opisthobranchia

Most Opisthobranch gastropods are marine plankton and lack a mineralized skeleton. Members that do have a skeleton, including the pteropoda, are usually small and either

cone-like or variable shaped because their shell is interior. There are no examples of pteropods and other opisthobranchs in the laboratory.

CEPHALOPODS

CLASSIFICATION & GEOLOGIC RANGES

Phylum Mollusca (Precambrian-Recent)

Class Cephalopoda (Cambrian-Recent)

Subclass Coleoidea (Devonian-Recent)

Subclass Nautiloidea (Cambrian-Recent)

Subclass Ammonoidea (Devonian-Cretaceous)

 

Class CEPHALOPODA

The cephalopods are a class of mobile mollusks, most of which are nektic or nekto-benthic. Cephalopods have a bilaterally symmetrical body, a prominent head, and a modified foot in the form of tentacles. Although during the Paleozoic and Mesozoic, cephalopods achieved great diversity and abundance in marine habitats, only two genera possessing skeletons are known today. See the example of a Nautilus.   Superficially the shell or conch of cephalopods resemble gastropods; however, most cephalopods coil in a plane, whereas gastropods are helicoiled. Furthermore, in cephalopods with an external conch, the coiled shell is chambered. 

Cephalopod Morphology

Some morphologic terms you should become familiar with are given below.

Phragmocone or conch: the external chambered shell.

Septum (plural septa): an internal partition which separates the chambers. 

Living chamber: the space between the aperture and the last septum.

Siphuncle: the tube connecting the living chamber with all previous chambers. The siphuncle is the plane of bilateral symmetry. See the example of the siphuncle on the Recent Nautilus. 

Suture: the outer edge of the septum (or juncture of septum with shell wall) which usually is expressed in outer wall of shell. The suture can be relatively straight as in Nautilus.   or fluted with saddles and lobes,   saddles are convex toward the direction of growth whereas lobes are concave. (See figure under subclass Ammonoidea).

Ribs: thickenings of external shell that may not be coincident with sutures. 

Keel: thickening along the outer (venter) margin.

Shape of External Shells

Several different shapes are common among fossil and extinct cephalopods. These include orthoconic or straight,   brevicone,   evolute planispiral,  involute planispiral, or heteromorphic. 

Morphology of Internal Shells

By definition, internal shells were surrounded by flesh during their development. Thus, they are commonly solid plates or nearly solid. Some terms that apply to internal shells include the phragmocone - the conical cavity in the anterior end of a belemnoid; and the rostrum - the part of a belemnoid enclosing the phragmocone and extending posterior of it.   The rostrum is solid calcite composed of radially arranged fibers exhibiting concentric growth bands.

Nonskeletal hardparts

A variety of non skeletal hard parts may be associated with cephalopods including Aptychi, which may serve as an operculum. Cephalopods may also have a beak and radula to aid in obtaining food. 

Subclass COLEOIDEA

The Coleoids are perhaps the most familiar cephalopod mollusks including as they do the octopods and squids. Coleoids are characterized either by an internal skeleton or by lacking a skeleton altogether. The internal shell of coleoids is almost exclusively straight (=orthoconic), although a few groups have a coiled shell. Others have a more complicated pattern such as in the cuttlebone.   The internal skeleton may consist of two parts, the outer rostrum and inner phragmocone as typified in the belemenites an order of squid-like animals which produced cigar shaped rostrum which has a conical depression at one end and a central cone-like phragmocone which is rarely found. 

Subclass NAUTILOIDEA

As with the ammonoids (see below), the nautiliods are an important group of cephalopods with an external shell. However, unlike the ammonoids, the nautiloids have living representatives in the genus Nautilus.   Nautiloid shells are external and are characterized by either straight or slightly wavy sutures. Nautiloid shells are either orthoconic,   or they are coiled, such as the Recent Nautilus; see also the fossil examples.   The siphuncle may be small or large, but is typically centrally located.

Subclass AMMONOIDEA

This is a very important extinct group of cephalopods which includes all forms with an external shell with fluted septa. Most are planispiral, but some may be heteromorphic (= not planispiral which can include orthoconic or a variety of shapes). The siphuncles are generally small and ventral in position. Division within the ammonoids is based upon the grades of suture fluting. There are three grades you will need to know which are illustrated and described below:

Figure 2 - Ammonoid Suture Patterns

Modified from McRoberts (1998)

Goniatite suture. Saddles and lobes are present. The goniatite suture is characterized by undivided rounded saddles and undivided angular lobes. Ammonoids with this type of suture are called goniatites. 

Ceratite suture. Saddles are undivided whereas the lobes are divided. Ammonoids with this type of suture are called ceratites. 

Ammonite suture. Both the saddles and lobes are divided. Ammonoids with this type of suture are called ammonites. Although many of the ammonites are coiled, there are

many genera such as Baculites,   which is heteromorphic and encompasses a variety of coiling shapes.

BIVALVIA

INTRODUCTION

This laboratory discusses two classes of molluscs: the bivalves and rostroconchs; of which the bivalves have the most robust fossil record. Although these two groups have species that are far too long-ranging for precise stratigraphic correlation and zonation, their morphologic attributes are very diagnostic of their diverse life-habits and paleoecology. As such, this laboratory deals with a minimum of classification (only to class level) and concentrates more on paleoecology.

Like other molluscs, these two classes have a fleshy mantle encasing the visceral mass

and a muscular foot. Unlike gastropods and cephalopods, bivalves secrete two shells rather than one. Additionally, bivalves have lost the radula, which is presumed to be a primitive feature among all mollusks. The Rostroconchs are similar in many regards to bivalves, especially in their hypothesized soft parts, a significant difference is that the shell is pseudobivalved.

CLASSIFICATION & GEOLOGIC RANGES

Phylum Mollusca

Class Rostroconchia (Cambrian-Permian)

Class Bivalvia (Cambrian-Recent)

Subclass Paleotaxodonta

Subclass Isofilibranchia

Subclass Pteriomorphia

Subclass Herteroconchia

Subclass Anomaldesmata

 

Class ROSTROCONCHIA

Rostrochonchs are a relatively minor Paleozoic group which may have an important phylogenetic position within the phylum Mollusca. Some authors suggest that rostroconchs evolved from an early monoplacophoran ancestor and gave rise to both bivalves and scaphopods, leaving the cephalopods and gastropods as descendants from a separate monoplacophoran stock.

Although they may have an internal anatomy similar to bivalves, rostroconchs are characterized by a single, pseudobivalved shell which encloses the mantle and muscular foot. The anterior part of shell has a gape from which the foot could probably emerge and an elongated tube on the posterior end called the rostrum which may have aided in water filtration. Although only one example is provided from the laboratory,   please examine the illustration below.

Figure 1 - General Rostrochonch Morphology

From McRoberts (1998)

Class BIVALVIA

Bivalves, sometimes called Pelecypods (meaning axe foot) or, in older literature, referred to as Lamellibranchs, are a very diverse and abundant group of molluscs which inhabit a variety of marine and non-marine environments. Their long geologic history and variety of forms have made them the popular subjects of many evolutionary and functional morphological studies.

For those who work on modern bivalves, often the characters such as the gill structure and even color patterns have taken prominence in classification. However, for those working on only the preserved hard parts of fossils, usually features such as differences in teeth provide the classification scheme. Unfortunately, because bivalves have many morphologic features with adaptive value, many of these features have arisen more than once. As a result, it is often difficult to erect a classification that reflects an evolutionary history. The classification scheme given above (which you are not responsible for) is derived in part from your text and is an attempt to incorporate both hard and soft part morphology.

The shell of bivalve molluscs is characterized by two calcareous halves, called valves, which can be composed of either calcite and/or aragonite. Some groups, such as the oysters,   are exclusively calcitic, while others, such as the pterioids,   have an aragonitic inner layer. The outermost layer of the bivalve shell, called the periostracum, is composed of a horny organic substance which in the example is the darker material only on the external part of the shell. 

The beak is located in the dorsal region of bivalves. The byssus or foot protrudes from the anterior of the shell, while the posterior the shell is the region of siphon protrusion (at least in some bivalves). The plane between the two valves (or commissural plane) is the plane of symmetry which separates the left from right valve. Note there is not an upper and lower valve (as in brachiopods) because most bivalves are oriented with their commissure plane vertical. Although this symmetry is retained in most bivalves,   the symmetry is secondarily lost in others. Note that in one of the specimens, there is close to a plane of symmetry within the valves.   This asymmetry corresponds to the living habit of the beasts, and those who have lost their original bilateral symmetry between the valves commonly live with their plane of commisure not perpendicular to the sediment surface.

Left or right valves can be determined by viewing the posterior end (as shown in the figure below).

Figure 2 - Determination of Left and Right Valve

 

The two halves of the bivalve shell are usually joined at the dorsal margin by a ligament which acts as a spring. The ligament may be internal, as in oysters, mussels, or scallops. Some internal ones consist of horizontal or vertical bands which sit in grooves.   Other ligaments may be external.   The hinge margin may also be occupied by a series of teeth and sockets collectively referred to as dentition (see below). The opening and closing of the shell are controlled by adductor muscles (which oppose the force of the ligament) that often leave physical scars on the valve interior (see below). Other muscles that leave scars include the pallial muscles which attach the mantle to the shell, in addition to smaller ones that control the siphons, foot, and/or byssus. General terms that you will need to know are given in the next section.

MORPHOLOGY

General Morphology

Beak: The region of initial growth of shell. The beak can be curved to either the anterior or, less commonly, the posterior. The general region of the beak is often called the umbone.

Auricle: A wing-like protrusion along the dorsal margin, this can be either anterior and/or posterior of the beak. See the wing-like projection in the examples. 

Byssal notch: Anterior depression below the auricle from which the byssal threads emerge. Such a notch can be viewed directly beneath the anterior auricle in this example. 

Escutcheon: A small curved area on the dorsal margin posterior to the beak. Both valves must be joined to view the escutcheon.

Lunule: A small curved area on the dorsal margin anterior to the beak.

Equivalved: Both valves being equal in size and shape.

Inequivalved: Two valves of unequal size and shape.

Equilateral: An individual valve that is symmetrical along its mid-line as in most brachiopods.

Inequilateral: Valves that are not symmetrical along their mid-line as is the case for most bivalve species.

Dentition and Ligaments

Cardinal teeth: The teeth immediately below the beak (see Figure 3 below).

Lateral teeth: The teeth extending laterally from the beak.

Edentulous space: Hinge region lacking teeth, usually present between the cardinal and lateral teeth.

Resilifer: A small depression along the hinge plate which holds an internal ligament; may be a single pit or consist of multiple pits.

Taxodont dentition: A series of small parallel to sub parallel teeth which are perpendicular to hinge line.

Heterodont dentition: having cardinal teeth and lateral teeth either in front and/or behind beak.

Desmodont dentition: having an internal ligament and a chondrophore, but usually lacking well defined teeth.

Schizodont dentition: having prominent bifurcating or diverging teeth.

Figure 3 - Bivalve Dentition

 

Musculature

Pallial line: Line of mantle attachment (see Figure 4 below). 

Pallial sinus: An indentation in the posterior part of the pallial line where the siphons can be retracted. 

Dimyrian: A valve having two adductor muscle scars; one anterior and one posterior. 

Isomyrian: A dimyrian shell where two adductor scars generally equal in size.

Anisomyrian: Dimyrian shell where the two adductors are of unequal size; usually the posterior scar is the larger of the two.

Monomyrian: A shell having only one adductor scar; which is usually a centrally positioned posterior adductor scar. 

Figure 4 - Interior Shell Markings

 

Feeding

Most bivalves are filter feeders, trapping suspended food particles as water passes through their gills. Only two groups, the nuculoids and cryptodonts, actively feed on organic material within the sediment and are thus true deposit feeders. Taxodont dentition is characteristic of deposit feeders.

Relations to Substrate

Bivalves have a variety of morphologic features that can be related to their particular life habit or mode of attachment to the substrate. We will examine several.

Infaunal

Burrowing: Shells are usually equivalved and isomyrian (or anisomyrian) with a

distinct pallial line. They include: the nuculoid burrowing deposit feeders, the shallow burrowing non-siphonate forms lacking a pallial sinus, and deep burrowing siphonate forms identified by a distinct pallial sinus.

Boring: Shells are usually thick, equivalved, and cylindrical in cross section. Some forms are moderately ornamented with ridges and stout spines  whereas others such as the "ship worms" are tubular in form.

Semi Infaunal

Byssally attached (endobyssate). Similar to many epifaunal byssate forms (see below), yet maximum shell width (inflation) is at mid-line of shell cross-section. Some forms can be elongated and fan-like with a reduced anterior area. Examples include pen shells,   and the mussel-like modiolids,   and some ark shells. The depth to which the bivalves are partially buried can often be deduced by looking for encrusting organisms that may have attached themselves above the sediment-water interface.

Epifaunal

Byssally attached (epibyssate). Shells can be either equivalved or inequivalved depending on their orientation to substrate during life. Usually, all epibyssate forms have a reduced anterior region. Some groups, such as the blue mussels, are similar to endobyssate forms except the maximum inflation is below the mid-line of the valves cross-section. Other forms may have a byssal notch and/or a well defined auricle,   or, as in the case of some arks, have a gape along the ventral margin.

Reclining. Shells are commonly inequivalved with a larger lower (usually the left) valve which is more inflated or convex while the upper valve may be planar. Some also exhibit spines, especially on the lower valve, to aid in stabilization in soft substrates in a manner similar to some brachiopods. Many have a small attachment area at beak where earliest growth stages were cemented.   The giant clam Tridacna,   who has photosymbionts similar to hermatypic scleractinian corals, is a recliner even though it had a functional byssus during its earliest juvenile stages.

Swimming. Shells are usually equilateral but not equivalved. The lower (usually the left) valve is usually slightly larger. Swimming forms are typified by having a greater umbonal angle (greater than 105°) than similar-looking epibyssate forms.

Furthermore, swimming forms typically have a single (monomyrian), large, centrally located adductor muscle. 

Cementing. Shells are commonly inequivalved with the lower (usually left) valve assuming the form of the object to which it is cementing, a condition called xenomorphism. In such cases, both valves are usually highly variable in shape, as in the common oysters   and other forms as well. Some groups such as the Cretaceous rudists   could reach very large sizes and were able to form reefs mimicking corals in both morphology and ecology.

ECHINODERMATA

From Eldredge (1991)

INTRODUCTION

The phylum Echinodermata consists of several types of complex organisms which show a general pentameral symmetry and have a well developed water vascular system.

Echinoderms are also characterized by their mesodermal skeleton. Echinoderms occur in a variety of morphologies including free-living forms such as starfish and sand dollars as well stalked forms such as sea lilies which are attached to the sea floor.

The first part of the lab will concentrate on the stalked echinoderms also called pelmatozoans. Pelmatozoans are exclusively marine and live in a variety of habitats of normal salinity. They are all filter-feeders. As a group, the pelmatozoans have been quite abundant in the geologic past especially the Paleozoic, yet since the close of the Mesozoic they have mainly relegated to deep-water, cryptic environments.

The second part of this lab will concentrate on the very diverse non-stalked echinoderms belonging to the subphyla Asterozoa and Echinozoa, and collectively referred to as free-living echinoderms. Similar to the pelmatozoans, the free-living echinoderms all have a mesodermal skeleton comprised of calcite plates and a complex water-vascular system including tube-feed. Unlike the pelmatozoans, the groups of this lab are quite abundant in the modern seas, occupying a large number environments by an equally large number of life-habits. Because of their abundance and diversity, the echinozoans will be the largest part of the lab.

CLASSIFICATION & GEOLOGIC RANGES

 Phylum Echinodermata (Precambrian -Recent)

Subphylum Crinozoa (Cambrian-Recent)

Class Crinoidea (Cambrian-Recent)

Subphylum Blastozoa (Cambrian-Permian)

Class Blastoidea (Silurian-Permian)

Class Rhombifera (Ordovician-Devonian)

Subphylum Asterozoa (Ordovician-Recent)

Class Asteroidea (Ordovician - Recent)

Class Ophiuroidea (Ordovician - Recent)

Subphylum Echinozoa (Precambrian?, Camb-Rec.)

Class Echinoidea (Ordovician - Recent)

Class Edioasteroidea (Cambrian-Carboniferous)

 

PELMATOZOAN GENERAL MORPHOLOGY

In general, the pelmatozoan skeleton can be dived into two main parts: The stem and the calyx. The stalk or stem is composed of numerous disks called columnals   which have a central hole called the lumen.   Stems are often secured to the substrate by means of a holdfast or root system.   The calyx (sometimes called theca), a cup-like structure as shown in these specimens,   which may or may not support a variety of arms.   As outlined below, the calyx is usually composed of a number of different kinds of plates, grooves, and pores; some of which are quite specialized

Appendage and Calyx Morphology

Ambulacral groove: one of the 5 radially arranged regions specialized for food gathering.

Brachial plates: arm plates; several different types depending on position relative to arm branch e.g., primibrachials and secundibrachials. See these fossil specimens. 

Brachioles: small erect food gathering appendages surrounding the edge of the ambulacrual area in blastoids.

Pinnules: small linear hair-like branches that may occur on each arm plate and also aid in food gathering.

Basal plates: the circlet of plates below and off-set to, and joining, the radial plates.

Infrabasal plates: secondary plates below basals.

Radial plates: below lowest brachial and above basal plates where ray terminates.

Interray plates: plates that are added between rays.

Lancet: ambulacral plate of blastoid, usually site of brachiole attachment.

Deltoid: small triangular or rhombahedral plate above the radial plates in blastoids.

Pores: openings for tube feet. 

Tegmen: Part of calyx occasionally with plates that resides above the attachment points of arms. Sometimes elevated into a anal pyramid.

Ray: trace of plates from arm through calyx; there are usually five (or multiples thereof) rays in pelmatozoans; ray terminates with radial plates (note the larger arrows in the figure below).

Figure 1 - Pelmatazoan Plate Arrangements

Modified from McRoberts (1991)

CRINOZOA & BLASTOZOA

 Phylum Echinodermata (Precambrian -Recent)

Subphylum Crinozoa (Cambrian-Recent)

Class Crinoidea (Cambrian-Recent)

Subphylum Blastozoa (Cambrian-Permian)

Class Blastoidea (Silurian-Permian)

Class Rhombifera (Ordovician-Devonian)

 

Subphylum Crinozoa and Class Crinoidea

Most crinoids consist of a calyx with arms supported by a stem. The arrangement of

arms and plates are the main criteria for subclass and lower division. The arms can be single or branched, and may be constructed of a single series of brachials (uniserial)   or composed of an alternating series of brachials (biserial),   and may also support pinnules.

The normal arrangement of plates consist of brachials, radials, and basals.   They can be dicyclic (having infrabasals) as in the example or monocyclic (without infrabasals) as in the example.

Crinoids can be divided into 4 subclasses: the Inadunates, Camerates, Flexibles, and Articulates (see your text book), only the articulates survive to the Recent. For an example of how large crinoids can be, look at this specimen. 

Subphylum Blastozoa

The two blasotzoan classes which are of importance include the Blastoidea and Rhombifera (= cystoids of some workers). Other blastozoan classes with a fossil record include the Diploporata, and Eocrinoidea. Together, all blastozoans have hydrospires, small folds under the lancet plates. The differences between each class is based primarily upon the pore and plate arrangement.

Class Blastoidea

Blastoids were attached by a stem to their substrate. The calyx of most species consists of 13 main plates: 5 deltoids, 5 radials, and 3 basals. Pores are restricted to the 5 ambulacral areas covered by lancet plates. The margins of the lancets were lined with brachioles. The mouth is centrally located on the top of the calyx (note Blastoids do not have a tegmen) and is surrounded by smaller holes for water vascular control called spiracles. 

Figure 2 - Blastoid and Rhombiferoid Morphology

From McRoberts (1998)

Class Rhombiferia

The Rhombifereans on the other hand have an irregular calyx with irregular shaped plates. The pores are not restricted to the ambulacral areas, but are commonly distributed over the calyx in rhombahedral patterns ("Rhomb pores") which overlaps two adjacent plates.

ECHINODERMATA

ASTEROZOA & ECHINOZOA

 

 Phylum Echinodermata (Precambrian -Recent)

Subphylum Asterozoa (Ordovician-Recent)

Class Asteroidea (Ordovician - Recent)

Class Ophiuroidea (Ordovician - Recent)

Subphylum Echinozoa (Precambrian?, Camb-Rec.)

Class Echinoidea (Ordovician - Recent)

Class Edioasteroidea (Cambrian-Carboniferous)

 

Free-Living Echinoderm Morphological Terms

The terms below are pertinent to most all of free-living echinoderms and even to stalked pelmatozoans. See the attached figures to make sure you can identify each structure as well as know its function.

Ambulacra: one of the five rays of an echinoderm which support the tube feet; in echinoids it is usually covered with numerous ambulacral plates.

Interambulacra: region between ambulacral regions.

Apical system: the circlet of 10 plates surrounding the anal system (see periproct).

Madreporite: a modified opening which commonly has several openings which serve to regulate water pressure.

Periproct: anal opening, usually on the aboral (anti oral) side.

Aristotle's lantern: the mouth, jaw, and teeth parts of an echinoid made up of 40 different skeletal elements.

Spine: rod or club-like structure used in locomotion and/or defense.

Tubercle: attachment structure (usually a knob) to receive a spine.

Subphylum ASTEROZOA

This Subphylum includes the star shaped, mobile benthic echinoderms. The subphylum has two major groups: asteroids and ophiuroids based on the presence or absence of a central disc.

Class ASTEROIDEA

The Asteroids, or starfish, have thick, hollow arms with prominent ambulacral grooves extending to the tips of the arms on the ventral side. In life, the grooves were lined with the tube feet. The mouth is located on the ventral (under) side, and the anus, when present, is located on the ventral side next to the madreporite (see above for a definition). See the Recent example,   making sure you can recognize the ambulacral grooves.

Class OPHIUROIDEA

The Ophiuroids, or brittle stars, are characterized by whip-like arms made of articulated plates. The plates resemble tiny vertebrae. Ophiuroids have a mouth centrally located on the ventral surface but lack an anus. They do, however, have a madreporite on the dorsal surface. Additionally, ophiuroids have ambulacra on the ventral side leading towards the mouth. See the examples,   making sure you can recognize the ambulacral regions of each appendage.

Subphylum ECHINOZOA

You will be responsible for three classes of echinozoans: echinoids, holothurians, and edioasteroids. Echinozoans occupy a variety of infaunal and epifaunal environments,

yet like their pelmatozoan relatives, they are stenohyaline and require normal marine salinities.

Class ECHINOIDEA

Echinoids, including sea urchins and sand dollars, generally have skeletons which are sub-spherical, hear-shaped, or disk-shaped. Like the crinoid calyx, they are composed of a mosaic of plates; unlike the crinoids, they are covered by spines. These are tiny bristles in some, but can be quite large in others. The spines generally detach from the main skeleton after death, because they are held to it only by non-mineralized ligaments. There are no arms, and the ambulacral areas (where the perforated plates are found) stretch from pole to pole. Echinoids can be further divided into two groups which you will be responsible.

Regular Echinoids

Regular echinoids have five-fold radial symmetry; mouth and periproct at opposite poles (oral and apical sides). Plates in interambulacral areas have well defined tubercles. See the example   and the plate arrangement, tubercles, spines, thickness of test, mouth and periproct, symmetry, and especially make sure you can identify the ambulacral vs. interambulacral regions. Regular echinoids are mostly epifaunal mobile grazers that sometimes occur in rocky subtidal and intertidal environments.

Figure 3 - Echinoid Morphology

From McRoberts (1998)

Irregular Echinoids

Irregular echinoids have bilateral symmetry; mouth toward anterior on ventral side, and periproct in posterior interambulacral area. Petals are conspicuous dorsal parts of ambulacral areas characterized by slit-like pores. Note that the anterior petal (ambulacral region) is cut by the plane of bilateral symmetry. Examine these examples   -  for things such as lack of symmetry, thickness of test, petals, mouth, and position of periproct.

Irregular echinoids occur primarily in infaunal environments. The depths at which individuals lived can sometimes be deduced by their external morphology.

Class EDIOASTEROIDEA

Edioasteroids have a globular or discoid skeleton composed of many small interlocking plates. The upper surface contains five radiating ambulacra covered with even smaller plates. The five radial ambulacra may be straight or arranged in a spiral pattern. The mouth is centrally located next to a small hydropore. The anus usually occurs on the same side as the mouth, but within an interambulacral region. Commonly, the outer margin is comprised of a ring of more tightly interlocking plates. See the specimen

encrusting the strophomenid brachiopod. 

ARTHROPODA

From Eldredge (1991)

INTRODUCTION

Arthropods are the most diverse phylum today and probably also in the geologic past. They are a highly specialized group which are characterized by their bilaterally symmetrical body, paired appendages and a chitinous (calcite in some groups) exoskeleton. As the exoskeleton once produced remains inert, arthropods must periodically shed their exoskeleton during molting and re-precipitate a larger one in order to accommodate their larger size.

Many arthropods may be familiar to you such as crabs, lobsters, barnacles, and insects, yet the fossil record of the phylum is dominated by few groups, particularly the trilobites, and to a lesser extent the eurypterids, and ostracodes. The trilobites in particular are unparalleled for their biostratigraphic utility for Cambrian and Ordovician and to a lesser extent Devonian sediments. Conversely, the eurypterids and ostracodes are more useful in determining ancient environments at least during mid to latter Paleozoic times.

CLASSIFICATION & GEOLOGIC RANGES

Phylum Arthropoda (Precambrian-Recent)

Superclass Trilobitomorpha (Cambrian-Permian)

Class Trilobita (Cambrian-Permian)

Order Polymerida (Cambrian-Permain)

Order Agnostida (Cambrian-Ordovician)

Superclass Crustacea (?Precamb., Cambrian-Recent)

Class Ostracoda (Cambrian-Recent)

Superclass Chelicerata (Cambrian-Recent)

Class Merostomata (Cambrian-Recent)

Order Xiphosurida (Cambrian-Recent)

Order Eurypterida (Ordovician-Permain)

 

TRILOBITOMORPHS

General Morphology

Like other arthropods, trilobitomorphs are characterized by numerous jointed and paired appendages. The calcitic and/or chitinous exoskeleton of trilobites consists of three lobes: a central axial lobe, and two lateral pleural lobes (see Figure 1 below). As shown in Figure 1, the exoskeleton of trilobites can be divided lengthwise into three regions: a fused head segment called a cephalon; a fused tail segment called a pygidium which sometimes bears spines,   but is normally completely fused with a smooth margin;   and a mid region or thorax consisting of numerous segments. Re-examine the previous images and be sure that you can recognize these morphologic features on a single specimen.

The cephalon also contains several unique features. The glabella is the extension of the axial lobe into the cephalic region and is often ornamented with furrows and ridges. Lateral to the glabella are the eyes which can be either of compound or single lens type. Forward of the glabella is the frontal area, a relatively flat region which sometimes bears pits. The terminal margin of the cephalic segment may be ornamented with genal spines. 

Figure 1 - General Trilobite Morphology

Modified from McRoberts (1998)

During molting, many trilobites split their exoskeleton along facial sutures which separates the fixed cheek from the free cheek. Depending on their position relative to the genal angle, these sutures can be of four types: (see Figure 2 below) opisthoparian terminating behind the genal angle, proparian terminating forward of the genal angle, gonatoparian dissecting the genal angle, and marginal along the cephalic margin.

Figure 2 - Trilobite Facial Suture Types

Modified from McRoberts (1998)

Paleoecology and Life Habits

Before any attempt at a paleoecologic or life-habit interpretation is made one must first recognize the nature of the fossil sample. As mentioned earlier, all arthropods periodically molt their exoskeleton to accommodate for larger size; as such, one individual may produce many molts or instars (or sometimes called exuvea). To determine if a trilobite fossil is a molt or body fossil see if the suture is split and the free cheeks are missing. If so, the fossil may be interpreted as a molt. If the suture is intact and there is no evidence of splitting, the fossil may be interpreted as a body fossil. Examine this image and see if you can identify it as a molt or a body fossil. 

Trilobites are very common in marine limestones and shales of the early Paleozoic, especially from the Cambrian Period. Most trilobites were epifaunal crawlers. Although they occupy a wide variety of exclusively marine habitats, specific life habits are difficult to discern by morphology alone. Nonetheless, several aspects of trilobite morphology can indeed provide some clue as to the life habit or activity. Examples include the elongated cephalic shield of the example which may have aided in ploughing through sediments.   Although most trilobites are considered to have been benthic, the small size and non-descript morphology of agnostid trilobites suggests that these (along with some others) may have been nektonic or nekto-benthic. Enrolling of trilobites may certainly have been a defensive mechanism. 

Taxonomy

According to some texts, trilobites are considered to have phylum status and are divided into eight Orders. A less radical classification which is used here (and in other texts) treats trilobites as a Superclass or Class with two orders: the Polymerida and the Agnostida. The Polymerida are by far the most diverse of the two in regards to species diversity and also morphologic and ecologic types. The Polymerids can be identified by their larger size, a well defined cephalic region with eyes and facial sutures, and a large number of thoraxic segments.   An easier way to identify Polymerids is by default; if its not a agnostid (easy to identify) then it's a Polymerid. All of the images you have seen thus far are Polymerids, here is another example from this diverse group. 

Agnostid trilobites are easily recognizable by their small size, few thoraxic segments (usually around two), and a cephalon without eyes which is superficially similar in morphology to the pygidium.   Furthermore, agnostids lack facial sutures.

CRUSTACEA & CHELICERATA

CLASSIFICATION & GEOLOGIC RANGES

Phylum Arthropoda (Precambrian-Recent)

Superclass Crustacea (?Precamb., Cambrian-Recent)

Class Ostracoda (Cambrian-Recent)

Superclass Chelicerata (Cambrian-Recent)

Class Merostomata (Cambrian-Recent)

Order Xiphosurida (Cambrian-Recent)

Order Eurypterida (Ordovician-Permain)

 

Superclass CRUSTACEA

Crustaceans are a diverse group of Arthropods that include familiar forms such as barnacles,   crabs,   and shrimp. They occur in a wide variety of marine and fresh-water habitats from the deep sea to ephemeral lakes and streams. Apart from the ostracodes (see below) and barnacles which have a calcite exoskeleton, most crustaceans have a limited fossil record. Crustaceans are characterized by having two pairs of antennae and gills and additional biramus appendages.

Class OSTRACODA

Although ostracodes are a minor zoological group, they are often found as fossils in large numbers. Although they occur in a variety of normal marine to freshwater environments, they typically characterize physically stressed environments such as hypersaline or brackish habitats. Ostracode species are often long-lived limiting the usefulness in biostratigraphy.

Ostracodes have a bivalved carapace enclosing the body which is usually calcified.   Similar to pelecypod bivalves, the left and right valves of ostracodes are joined on the dorsal margin by a flexible ligament. The interior of the ostracode valve often supports muscle attachment scars which are of two types: (i) the centrally located adductor muscle scars, and (ii) the dorsally located operator muscle scars. The operator muscles control the various appendages of the ostracode animal. The exterior of an ostracode valve may be smooth or ornamented with various spines, knobs, or pits. Apart from the differences outlined above, ostracodes differ from bivalves in that they, the ostracodes, are usually smaller and do not have growth lines in their shell (recall arthropods secrete their exoskeleton at once and not by incremental growth).

Superclass CHELICERATA

The Cheilicerata include all arthropods with pincer-like chelicerae which aid in food gathering and/or locomotion and uniramus appendages. Common chelicerate

organisms that are still with us include scorpions, horseshoe crabs,   and spiders.

Class MEROSTOMATA

Merostomes are a numerically minor group both today and in the geologic past. Although only three living genera are known today, all belonging to the horseshoe crabs, the merostomes were only moderately diverse during the Early Paleozoic due to the abundance of eurypterid forms. The skeleton of merostomes is characterized by three main regions: (i) the prosoma which is a fused cephalon and thorax combined, (ii) the opisthosoma which incorporates the abdomen and (iii) the tail spine called the telson. A unifying character among cheliceratids, all merostomes have two prosomal (preoral) pincer-like appendages called chelicerae for gathering and crushing food. The prosoma also have up to five pairs of walking legs behind the chelicerae. Two orders you should know are the Eurypterida and Xiphosurida

Order EURIPTERIDA

The eurypterids include small to large-sized merostomes with a scorpion-like exoskeleton (see Figure 3 below). Although they occur in a variety of normal marine to freshwater environments, they, like the ostracodes, are known from physically stressed environments such as hypersaline or brackish habitats. The eurypterids were especially common during the Silurian period and were known to occur in great numbers from the nearby Manlius Syracuse Formations.

Figure 3 - General Eurypterid Morphology

From McRoberts (1998)

Eurypterids have two pairs of eyes on the prosoma: the smaller, centrally located ocelli, and (ii) the larger lateral compound eyes. The telson are often found as disarticulated remains. The eurypterids have one pair of large appendages which served as swimming paddles behind the uniramus walking legs. The prosomal appendages can clearly be seen on the following image. Examine closely this well preserved, and rather complete specimen. 

Order XIPHOSURIDS

The xiphosurids are characterized by a relatively large prosoma and partially fused opisthosoma. Although the common horseshoe crab Limulus is a typical Recent example, representatives are known as far back as the Cambrian. The xiphosurids have apparently always been confined to near-shore marine environments. Like the

eurypterids, xiphosurids have two sets of eyes: a compound pair and smaller ocelli. 

ETC...

Very rarely, other non calcitized arthropods are preserved as fossils. The hexapods (including the insects), which are the most diverse superclass of any phylum, very rarely are fossilized due to their delicate exoskeleton.

Miscellaneous Fossil Groups

 

From Eldredge (1991)

INTRODUCTION

This laboratory considers several different fossil groups who's biologic affinities to other modern groups is in doubt. Most of these fossil groups occur as Paleozoic plankton, and their utility (especially the graptolites and conodonts) are in their biostratigraphic resolution which is on the order of 2.5 MY or less.

CLASSIFICATION & GEOLOGIC RANGES

Phylum Hemichordata

Class Graptolithina (Cambrian - Pennslyvianian)

Order Dendroidea (Cambrian - Pennslyvianian)

Order Graptoloidea (Ordovician - Devonian)

Phylum uncertain

Conodontomorphia (Cambrian - Triassic)

Hyolithia (Cambrian - Permian)

Tentaculitida (Ordovician - Devonian)

Conularia (Cambrian-Triassic)

 

 

GRAPTOLITES

The graptolites are considered by many to belong to the phylum Hemicordata, the phylum which also includes the Recent Rhabdopluerids. Assignment to the Hemichordata is based upon the presence of stolon, a small tube similar to a notochord in chordates which transverses the length of the noncolonial forms and connects the individuals of the colonial forms. Graptolites are exclusively colonial organisms in which each individual is called a zooid. The zooids may serve different functions with regards to reproduction and feeding.

Graptolite Morphology

Graptolite morphology is highly varied. Two basic morphologies include the dendroid type and graptoloid type. Both types consist of small conical cups called thecae in which each zooid is housed and is arranged along a linear series. Each linear series of connected thecae forms a stipe. Together, the skeleton comprising the stipe and thecae is called the rhabdosome. The first or initial theca from which all others bud is called the sicula. The dendroid graptolites are constructed by numerous branching stipes which are sometimes connected by rod-like structures called dissepiments. The graptoloid type consists of one to four stipes and are characterized by small thread-like structure connected to the sicula called the nema. See the excellent example showing this morphology in three dimensions (§12.1).

Graptolite Classification

Classification of graptolites is based on many characters such as the number of stipes, arrangement and orientation of thecae and any specilazed structures. For the Dendroids (§12.2-§12.4) classification is based upon branching arrangement and colony morphology. For the Graptoloids, the rhabdosome may take on a number of different morphologies. Pendant forms are the most primitive where the stipes hang downward from the nema such as Didymograptus (§12.5). Horizontal forms such as Monograptus (§12.6) are when the stapes stick laterally away from the nema. Reclining forms such as Dicellograptus (§12.7) are more advanced and are characterized by the stipes reclined upwards from the nema. The reclining condition may be taken to the extreme in the Scandent form where two or more stipes may fuse to produce biserial or tetraserial rhabdosomes with the theca pointing upwards (§12.8). You should examine the additional graptolites provided (§12.9-§12.14) and make sure you can identify all the morphologic features discussed above.

Graptolite Paleoecology

Graptolites are exclusively marine organisms which occurred from the Middle Cambrian through Upper Carboniferous. They are particulary abundant and are excellent biostratigraphic indices of the Ordovician and Silurian. Although they occur in a variety of lithofacies suggesting a pelagic planktonic life-mode, they are most commonly found in deep water black shale facies. In these environments, graptolites are preserved as compressed thin carbon films.

CONODONTS

Conodonts are small microfossils made of calcium phosphate which usually occur as disarticulated elements scattered throughout sedimentary rocks of the Paleozoic and early Mesozoic. Because they are found as disassociated elements, and are all extinct their taxonomic affinity is in question; yet they may belong to extinct group of organisms similar to some chordate bearing worms. Individual conodont elements belong to natural groupings called assemblages which are often found together.

Conodont Morphology

The individual elements are composed from a variety of small cones, bars, and blades or platforms some of which bear small teeth-like structures called denticles. Generally, conodonts can be grouped into three main morphotypes that are listed below (see also accompanying figure) and can be found on the slide (§12.13).

Coniform elements: consist of a single cone or cusp which has a small basal cavity. (§12.15)

Ramiform elements: consist of bars with a central cusp and denticles extending on either side of cusp. Usually, a basal cavity can be recognized. (§12.16)

Pectiniform elements: includes diverse forms bearing a platform, and numerous denticles, one of which may be an anterior cusp. Usually, a basal cavity can be recognized. (§12.17 and §12.18)

Conodont Paleoecology

Conodonts are exclusivly marine and have been recovered from a variety of paleonvironments. Their presence in near shore to relatively deep environments suggests that they were pelagic (either nektic or planktic). Other examples of conodonts can be found in the additional slide (§12.19).

CONULARIDS

Although there is some controversy in regards to the systematic position of the conularids, most workers today place them with the scyphozoan cnidarians rather than the molluscs. The exoskeleton of conularids is composed of chitin and in outline is pyramidal with four sides. The exterior surfaces of conularids normally have finely spaced longitudinal ribs. The interior of conularids may have thickenings or septa developed. In life, conularids lived attached apical end down to the substrate. A couple of examples are provided (§12.20).

HYOLITHIDS

It is uncertain as to what phylum the hyoliths belong. Until recently they have been classified as mollusks or worms, some prefer toconsider them as a separate phylum, and your text chose to ignore the group altogether. Hyoliths have a bilaterally symmetrical exoskeleton composed of a tapering conical (or pyramid) conch which is closed at one end (posterior) and has an open end (anterior) which may be closed by an operculum. In cross section, the cone of hyoliths may be either triangular or semicircular. The skeleton of hyoliths is composed of calcium carbonate. One group of hyoliths has two anterior bar-like protrusions called helens. Several examples are provided (§12.21).

TENTACULITIDS

Tentaculitids are a group of small animals which lived in a conical shaped exoskeleton composed of calcium carbonate. Like the hyoliths, they have been variously classified as mollusks or worms; unfortunately little is known about this extinct group which may belong to its own phylum. The exoskeleton of the tentaculitids may be relatively smooth as in the genus Styliolina (§12.22) or may have regularly spaced ribs or ridges as in the genus Tentaculites (§12.23-§12.25)

 

Trace Fossils

INTRODUCTION

Trace fossils (also called ichnofossils or lebenspuren) are the evidence of animal's activity. Unlike molds and casts which are evidence or replicas of skeletal remains or body impressions, trace fossils are sedimentologic or lithologic disturbance from an animal's (or plant's) activity such as resting, locomotion, or feeding.

The utility in trace fossils comes not from their biostratigraphic value, but instead their use in the interpretation of paleoenvironments. All too often, the organism that

produced the trace is unknown. Given that trace fossils reflect activity, many different organisms doing the same thing can produce similar traces. Likewise, an organism engaged in different activity can leave more than one trace.

CLASSIFICATION

Ichnofossils

Resting & Hiding Traces

Dwelling Traces

Locomotive Traces

Feeding Traces

-

-

Ichnofacies

Scoyenia Ichnofacies

Trypanites Ichnofacies

Skolithos Ichnofacies

Cruziana Ichnofacies

Zoophycos Ichnofacies

Nereites Ichnofacies

 

 

  

Bioturbation and Ichnofabric

Bioturbation can be defined as the disturbance of sediments due to biologic activity. An important component in understanding the activity of ancient organisms is an estimation of trace fossil abundance which in turn may offer clues as to the environment during deposition of the sediments (see Fig. 13.1). For example, in paleoenvironments that were unfavorable to trace-making organisms, the original sedimentary bedding or laminations will be left intact (see §13.1). As paleoenvironmental conditions improve, bioturbation activity increases leaving the original laminations disturbed (e.g. §13.2) to the point at which no primary bedding is observable (e.g. §13.3).

Morphology of Ichnofossils

The morphology of trace fossils can be described with respect to their position relative to their original depositional surface. Please see Figure 13.2 below and aquatint yourself with the various terms applied to trace fossil morphologies.

Activity Traces

Locomotive Traces (Repichnia): usually straight or slightly curved trails in addition to tracks and trackways. See the tracks (§13.4 and §13.5) and horizontal burrows called Planolites (§13.6).

Resting and Hiding Traces (Cubichnia): characterized by the fillings of shallow excavations that mimic the morphology of the trace maker. See Rusophycus (§13.7) for an example. Given the size and shape of the example (§13.7), what organism do you think may have made it?

Dwelling Traces (Domichnia): this group includes burrows, borings, or other excavations. They can be vertical unbranched cylinders or U-shaped. See Skolithos (§13.8) for a vertically oriented tubular burrow and the larger burrows (§13.9 and §13.10) made by shrimps and borings ( §13.11) made by Recent pholad bivalves.

Feeding Traces (Fodinichnia): Includes the burrows of sediment feeders usually with a distinct three-dimensional morphology. They may be dendritic or multibranched or

dendritic and take on other geometric patterns. See Zoophycos or Taonorus §13.12 to §13.14. Note on these traces the U-shaped backfill is called sprieten. Other feeding traces include Thalassanoides (§13.17) and Ophiomorpha (§13.18) which consists of large vertical and horizontal branching tubes.

Additionally, trace fossils inductive of feeding behavior (and diet) include predatory borings (e.g. §13.17 and §13.18) and fossilized excrement (called coprolites). Smaller fecal pellets (microcoprolites) are a common constituent in many sediments. See example §13.19 for examples of Triassic microcorprolites that were probably deposited by anomurian crustaceans (shrimps and crabs).

Grazing Traces (Pascichnia): Generally grazing burrows are two-dimensional features which occur along bedding surfaces as a spiral, S-shaped series of curves, or other geometric pattern. Grazing organisms are efficient feeders. Rarely do grazing burrows cross paths. No examples, sorry.

Paleoecology and Ichnofacies

An ichnofacies is a recurring assemblage of one or more ichnofossils which are characteristic of a particular environment. Trace fossils within a given inchnofacies often have similar morphologies which is presumably due to a similar activities of the fossil organisms which made them. Ones you will be responsible include:

Scoyenia Ichnofacies: These are nonmarine trace fossils that mainly include foot prints, trails, and trackways which were originally made in moist sediments.

Trypanites Ichnofacies: The Trypanites ichnofacies is characterized by mostly dwelling borings into lithified sediments in the intertidal to shallow subtidal zone.

Skolithos Ichnofacies: Sometimes grouped together with the Glossifungites ichnofacies, the Skolithos ichnofacies occurs in soft or firm (but not lithified) within the intertidal or shallow subtidal zone. The Skolithos ichnofacies is characterized by vertical dwelling burrows and tubes (some which may be U-shaped) that can extend many centimeters into the sediment.

Cruziana Ichnofacies: The Cruziana ichnofacies are characterized by simple locomotion traces with some U-shaped dwelling and shallow resting and hiding traces. The Cruziana ichnofacies is common in middle to outer shelf clastic settings.

Zoophycos Ichnofacies: The Zoophycos ichnofacies commonly contain three-dimensional feeding traces which were constructed by a variety of organisms in often poorly sorted and unlithified sediments. The Zoophycos ichnofacies is common below wave base in clastic shelf environments.

Nereites Ichnofacies: The Nereites Ichnofacies is characterized by an abundance of grazing traces and occasional three-dimensional feeding traces. The Nerites ichnofacies is occurs in deep-water (typically bathyal or abyssal) environments often is sediments interpreted as low-oxygen.

Geologic Time Scale

Modified from McRoberts (1998)

Glossary of Invertebrate Paleontology Terms

From the list below, select the letter that corresponds to the first letter of the word that you wish to look for.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

abdomen - Region of the body furthest from the mouth. In insects, the third body region behind the head and thorax.

 

ambulacra - Row of tube feet of an echinoderm.

 

anus - End of the digestive tract, or gut, through which waste products of digestion are excreted, as distinct from the mouth.

B

benthic - Organisms that live on the bottom of the ocean are called benthic organisms. They are not free-floating like pelagic organisms are.

 

biramous - Arthropod appendages that are biramous have two branches, an outer branch and an inner branch. These branches may have separate functions; in crustaceans, for instance, the inner branch of a leg is used for walking, while the outer branch may be paddle-shaped or feathery and often functions as a gill. Contrast with uniramous.

 

blood - Fluid which circulates throughout the body, distributing nutrients, and oxygen as well in many animals.

 

book lung - A set of soft overlapping flaps, covered up by a plate on the abdomen, through which oxygen is taken up and carbon dioxide given off. Characteristic of many terrestrial arachnids such as scorpions and spiders.

 

brain - Collection of nerve cells usually located at the anterior end of an animal, when present at all. The nerves coordinate information gathered by sense organs, locomotion, and most internal body activities.

C

cephalon - In trilobites, the head shield bearing the eyes, antennae, and mouth. More info?

 

chaetae - Stiff bristles characteristic of annelids.

 

chela - The claw of an arthropod.

 

chelicera - The first pair of appendages of a chelicerate arthropod. Originally a short clawed appendage, the chelicerae of many arachnids are highly modified for feeding; in spiders, for instance, they are modified into poisonous fangs.

 

clitellum - In annelids, a swelling of the body towards the head of the animal, where the gonads are located. Both oligochaetes and leeches have a clitellum.

 

cnidocyst - The "stinging cell" of a cnidarian.

 

coelom - Fluid-filled cavity within the body of an animal; usually refers to a cavity lined with specialized tissue peritoneum in which the gut is

suspended. The structure and development of the coelom is an important character for recognizing major groups of animals.

 

compound eye - Found in many but not all arthropods, a compound eye is composed of a large number of small, closely packed simple eyes (ommatidia), each with its own lens and nerve receptors.

 

cuticle - In animals, a multilayered, extracellular, external body covering, usually composed of fibrous molecules such as chitin or collagen, and sometimes strengthened by the deposition of minerals such as calcium carbonate.

D

E

ectoderm - The outer basic layer of tissue in those animals with true tissues. In vertebrates, for instance, the embryonic ectoderm differentiates into the skin and also the nervous system.

 

endoderm - The innermost basic layer of tissue in those animals with true tissues. Forms the gut and its derivatives: in vertebrates, these include the liver, trachea, and lungs.

 

epidermis - The outermost layer of skin.

 

epithelium - Layer of cells which lines a body cavity; cells may be ciliated or unciliated, and may be squamous (flat, scale-shaped), cuboidal (cube-shaped), or columnar (column-shaped). Your stomach and cheeks are lined with epithelium.

 

esophagus - That portion of the gut which connects the pharynx to the stomach.

F

G

gastrodermis - In cnidarians, the endodermis which lines the gut cavity. The term is often used instead of endodermis since cnidarians only have two tissue layers instead of three.

 

gill - In aquatic animals, highly vascularized tissues with large surface area; these are extended out of the body and into the surrounding water for gas exchange.

 

gill arches - Stiffenings which support the flesh between the gill slits of chordates. In most vertebrates, the first gill arches have been modified to form the jaw, and in tetrapods, the inner ear bones.

 

gill slit - A slitlike or porelike opening connecting the pharynx of a chordate with the outside of the body. Gill slits may contain the gills and be used for gas exchange, as in most fish, but may also be used for filter-feeding, or may be highly modified in land-dwelling vertebrates.

 

gnathobase - The expanded and hardened base of the appendage of many arthropods, notably trilobites, crustaceans, and marine cheliceramorphs. Used to macerate food items before ingestion.

 

gut (enteron) - Body cavity formed between the mouth and anus in which food is digested and nutrients absorbed; it consists of the mouth, pharynx, esophagus, stomach, intestine, and anus, though some animals do not have all these regions.

H

head - That part of the body at the "front" end, where the brain, mouth, and most sensory organs are located.

 

heart - Muscular pump which circulates the blood.

I

intestine - The portion of the digestive tract between the stomach and anus; it is the region where most of the nutrients and absorbed.

J

jaw - Often loosely applied to any movable, toothed structures at or near the mouth of an animal, such as the scolecodonts of annelids. In vertebrates, the jaw is derived from the first gill arch.

 

jointed - When stiff body parts are connected by a soft flexible region, the body is said to be jointed.

K

L

librigenae - The "free cheeks"; separate, detachable portions of the trilobite cephalon.

 

lophophore - Complex ring of hollow tentacles used a feeding organ. The tentacles are covered by cilia, which generate a current to bring food particles into the mouth. The structure is only found in the brachiopods, phoronids, and bryozoans.

M

mesoderm - In animals with three tissue layers (i.e. all except sponges and cnidarians), the middle layer of tissue, between the ectoderm and the endoderm. In vertebrates, for instance, the mesoderm forms the skeleton, muscles, heart, spleen, and many other internal organs.

 

mesogloea - Jellylike material between the outer ectoderm and the inner endoderm of cnidarians. May be very thin or may form a thick layer (as in many jellyfish)

 

mouth - Front opening of the digestive tract, into which food is taken for digestion. In flatworms, the mouth is the only opening into the digestive cavity, and is located on the "belly" of the worm.

 

mucus - Sticky secretion used variously for locomotion, lubication, or protection from foreign particles.

 

muscle - Bundle of contractile cells which allow animals to move. Muscles must act against a skeleton to effect movement.

 

myotome - Segment of the body formed by a region of muscle. The myotomes are an important feature for recognizing early chordates.

N

nematocyst - Older name for a cnidocyst.

 

neuron - A specialized cell that can react to stimuli and transmit impulses. A neuron consists of a body which contains the nucleus; dendrites, which are short branches off the body that receive incoming impulses; and a long axon which carries impulses away from the body and to the next neuron.

 

nerve - A bundle of neurons, or nerve cells. More properly, it is a bundle of axons.

 

nerve cord - Primary bundle of nerves in chordates, which connects the brain to the major muscles and organs of the body.

 

notochord - Characteristic of chordates, the notochord is a stiff rod of tissue along the back of the body. In vertebrates, the backbone is deposited around the notochord and nerve cord.

O

organ - Collection of tissues which performs a particular function or set of functions in an animal's body. The heart, brain, and skin are three organs found in most animals. Organs are composed of tissues, and may be organized into larger organ systems.

 

operculum - Small disk-like cover or lid of an aperture, commonly found in cheilostomes.

 

organ system - Collection of organs which have related roles in an organism's functioning. The nervous system, vascular system, and muscle system are all organ systems.

 

osculum - The main opening through which filtered water is discharged. Found in sponges.

P

papilla(e) - Cellular outgrowths. These look like little bumps or fingers on the surface of cells.

 

parapodia - A sort of "false foot" formed by extension of the body cavity. Polychaetes and some insect larvae have parapodia in addition to their legs, and these provide extra help in locomotion.

 

pedipalps - The second pair of appendages of cheliceromorphs. In many arachnids, such as spiders, the pedipalps are enlarged in the male and used for copulation.

 

pharyngeal slits - Characteristic of chordates, pharyngeal slits are openings through which water is taken into the pharynx, or throat. In primitive chordates the pharyngeal slits are used to strain water and filter out food particles; in fishes they are modified for respiration. Most terrestrial vertebrates have pharyngeal slits only in the embryonic stage.

 

pharynx - Cavity in the digestive tract just past the mouth itself. May be muscularized for sucking or swallowing in various animals.

 

pleurae - In trilobites and other arthropods, pleurae are elongated flat outgrowths from each body segment, that overlie and protect the appendages.

 

pore - Any opening into or through a tissue or body structure.

 

proboscis - Elongated organ, usually associated with the mouth. The proboscis is an important feeding appendage in echiurans.

 

pygidium - In trilobites, the posterior division of the body, formed by fusion of the telson with one or more posterior pleurae.

Q

R

S

segmentation - In many animals, the body is divided into repeated subunits called segments, such as those in centipedes, insects, and annelids. Segmentation is the state of having or developing a body plan in this way.

 

septum - Partition which divides up a larger region into smaller ones, such as in the central body cavity of some anthozoa.

 

siphon - Opening in molluscs or in urochordates which draws water into the body cavity. In many molluscs, the siphon may be used to expel water forcibly, providing a means of propulsion.

 

skeleton - Support structure in animals, against which the force of muscles acts. Vertebrates have a skeleton of bone or cartilage; arthropods have one made of chitin; while many other invertebrates use a hydrostatic skeleton, which is merely an incompressible fluid-filled region of their body.

 

spicule - Crystalline or mineral deposits found in sponges, sea cucumbers, or urochordates. They are structural components in many sponges, and may serve a protective function in other organisms.

 

spiracle - In insects and some other terrestrial arthropods, a small opening through which air is taken into the tracheae. Insects have several spiracles, arranged along the sides of the abdomen.

 

spongocoel - Central body cavity of sponges.

T

telson - The last segment of the abdomen in many arthropods. May be flat and paddlelike, buttonlike, or long and spiny, as in the horseshoe crabs.

 

tentacles - Appendages which are flexible, because they have no rigid skeleton. Cnidarians and molluscs are two kinds of orgnaisms which may have tentacles.

 

thorax - In insects, the second body region, between the head and thorax. It is the region where the legs and wings are attached.

 

tissue - A group of cells with a specific function in the body of an organism. Lung tissue, vascular tissues, and muscle tissue are all kinds of tissues found in some animals. Tissues are usually composed of nearly identical cells, and are often organized into larger units called organs.

 

tracheae - Internal tubes through which air is taken for respiration. Vertebrates with lungs have a single trachea carrying air to the lungs, while insects and some other land-living arthropods have a complex network of tracheae carrying air from the spiracles to all parts of the body.

 

tube feet - Extensions of the water-vascular system of echinoderms, protruding from the body and often ending in suckers. May be used for locomotion and/or for maintaining a tight grip on prey or on the bottom.

 

tubercle - Any small rounded protrusion. In pycnogonids and some cheliceramorph arthropods, the central eyes are carried on a tubercle.

U

uniramious - Among arthropods, uniramous refers to appendages that have only one branch. Insects, centipedes and millipedes, and their relatives are uniramous arthropods; land-living chelicerates such as scorpions, spiders, and mites are also uniramous but probably descended from ancestors with biramous appendages. Contrast with biramous.

V

vascular - Refers to a network of tubes which distribute nutrients and remove wates from the tissues of the body. Large multicellular animals must rely on a vascular system to keep their cells nourished and alive.

 

vertebra - A component of the vertebral column, or backbone, found in vertebrates.

W

X

Y

Z

zooaria - The colony of bryozoan animals.

 

zooecia (zooecium singular) - Bryozoan living chambers constructed by a colony of zooids. The zooecium is he living chamber constructed by one bryozoan individual.

 

zooid - Individual animal or member in a bryozoan colony.

 

zooxanthellae - Symbiotic dinoflagellates in the genus Symbiodinium that live in the tissues of a number of marine invertebrates and protists, notably in many foraminiferans, cnidarians, and some mollusks.

 

REFERENCES

CITED

Boardman, Richard S., Cheetham, Alan H. & Rowell, Albert J. (1987). Fossil Invertebrates. Blackwell Scientific Publications. Palo Alto, California.

Clarkson, E. N. K. (1986). Invertebrate Paleontology and Evolution. Allen & Unwin Ltd. London.

Eldredge, Niles. (1991). Fossils:The Evolution and Extinction of Species. Harry N. Abrams, Inc. New York.

McRoberts, Christopher. (1998). Laboratory Notes. Invertebrate Paleontology. State University of New York, College at Cortland.

Stanley, Steven M. (1993). Exploring Earth and Life Through Time. W. H. Freeman and Company. New York.

Links to Some Interesting Paleontology Web Sites

UC Berkeley Museum of Paleontology

http://www.ucmp.berkeley.edu/

 Paleontological Research Institute. A local paleontological institution with lots of educational resources and links.

http://www.museumoftheearth.org/collections/index.php

Learning from the Fossil Record . A web site devoted to paleontological education, aimed at primary and secondary school educators.

http://www.ucmp.berkeley.edu/fosrec/