Invertebrate Paleontology Tutorial.doc

8/17/2019 Invertebrate Paleontology Tutorial.doc

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TopicsTaphonomy & Preservation

Protista, Eubacteria, & Porifera

Cnidaria

Bryozoa

Brachiopoda

Cephalopoda, Gastropoda & otherMolluscs

Bivalve M olluscs

Echinodermata

Arthropoda

Miscellaneous Foss il Groups

Trace F ossils

http://paleo.cortland.edu/tutorial/Taphonomy%26Pres/taphonomy.htmhttp://paleo.cortland.edu/tutorial/Protista/protista.htmhttp://paleo.cortland.edu/tutorial/Cnidarians/cnidarians.htmhttp://paleo.cortland.edu/tutorial/Bryozoans/bryozoans.htmhttp://paleo.cortland.edu/tutorial/Brachiopods/brachiopoda.htmhttp://paleo.cortland.edu/tutorial/Ceph%26Gast/ceph%26gast.htmhttp://paleo.cortland.edu/tutorial/Ceph%26Gast/ceph%26gast.htmhttp://paleo.cortland.edu/tutorial/Bivalves/bivalvia.htmhttp://paleo.cortland.edu/tutorial/Echinoderms/echinoderms.htmhttp://paleo.cortland.edu/tutorial/Arthropods/arthropods.htmhttp://paleo.cortland.edu/tutorial/misc%20fossils/miscfossils.htmhttp://paleo.cortland.edu/tutorial/Trace%20Fossils/tracefossils.htmhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/taphonomy.htmhttp://paleo.cortland.edu/tutorial/Protista/protista.htmhttp://paleo.cortland.edu/tutorial/Cnidarians/cnidarians.htmhttp://paleo.cortland.edu/tutorial/Bryozoans/bryozoans.htmhttp://paleo.cortland.edu/tutorial/Brachiopods/brachiopoda.htmhttp://paleo.cortland.edu/tutorial/Ceph%26Gast/ceph%26gast.htmhttp://paleo.cortland.edu/tutorial/Ceph%26Gast/ceph%26gast.htmhttp://paleo.cortland.edu/tutorial/Bivalves/bivalvia.htmhttp://paleo.cortland.edu/tutorial/Echinoderms/echinoderms.htmhttp://paleo.cortland.edu/tutorial/Arthropods/arthropods.htmhttp://paleo.cortland.edu/tutorial/misc%20fossils/miscfossils.htmhttp://paleo.cortland.edu/tutorial/Trace%20Fossils/tracefossils.htm


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Geologic Time Scale

Glossary

References

Links to other Paleontology Pages on the WWW

INTRODUCTION

As fossils are t he p reserved remains of ancient organisms or their traces, understanding the p rocess

From Eldredge (1991)

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of preservat ion, and more i mportantly, being able t o recognize and identify fossil remains af ter t heirdiscovery is an integral part of paleobiology. Protective co ver ( sediments) and stabilizing chemicalenvironments ar e o f prime importance i n the p reservation of once l iving organisms. Due t o the

process of aerobic d ecay a nd physical/chemical destruction, most animals l eave n o evidence of theirexistence.

In order to make a co rrect interpretation of taphonomic p rocesses and mode o f preservation, it isoften necessary to have a prior knowledge o f the st ructural features or m orphology of originalskeleton in addition to knowing its ori ginal mineralogical composition. This l imitation shoulddiminish a s you become familiar w ith the va rious fossil groups t hroughout the sem ester.

TAPHONOMY

Taphonomy is t he st udy of what happens t o an organism after i ts d eath and until its d iscovery as afossil. This i ncludes d ecomposition, post-mortem transport, burial, compaction, and other c hemical,

biologitaphonomic p rocesses that have t aken place can o ften lead to a b etter understanding ofpaleoenvironments an d even life-history of the o nce-living organism.

In addition, understanding which t aphonomic p rocesses a f ossil occurrence ha s un dergone, and towhat degree, may have implication on interpreting the si gnicance o f the f ossil deposit and clearerunderstanding of the b iases in the sam ple.

An outline of the p athways aff ecting the p reservation of once l iving organisms can be foundin Figure 1 below. As d iscussed below, this encompasses bot h the p rocessesof biostratinomy and diagenesis .

Figure 1 - The eld of Taphonomy as i t relates t o st eps in transformation from livingorganisms t o fossils.


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Modified from McRoberts (1998)

Processes t hat occur between the d eath of an organism and its s ubsequent burial in the se diment aretermed biostratinomy . Generally, this i ncludes t he d ecomposition and scavenging of the a nimal'ssoft parts, and at least some am ount of post-mortem transport. Such things as t he am ount of shell

breakage d mortem transport. For example, the shell-hash or coquina has experienced a signicant amountof shell breakage and probably post-mortem transport suggesting deposition in high energy

environments; whereas, the art iculated plant remains are i ntact su ggesting little o r n o post-mortem transport and deposition in a ver y low energy and oxygen-free env ironment. In Table1 b elow are v arious t aphonomic i ndicators an d their env ironmental implications.

The p hysical and/or chemical effects after burial are c alled diagenesis . This i s t he real m in whichdissolution, replacement, or r ecrystallization of original shell material occurs, as ca n the f ormation ofmolds and casts. A more d etailed description of diagenesis w ith regards t o fossil preservation in thenext section.

Table 1

Summary of Taphonomic Indicators and TheirPaleoenvironmental Implications

TAPHONOMICIMPLICATIONS

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FEATURE

Abrasion

The wearing-down of skeletons owing to d ifferential movement with respect tosediments i s an indicator of environmental energy. Signicant abrasion is m ostcommonly found on skeletal material collected from beaches, or areas of strongcurrents or wave act ion.

ArticulationMulti-element skeletons a re soon disarticulated after d eath. Articulatedskeletons, then, indicate r apid burial or otherwise r emoving the skel eton fromthe effects of energy of the o riginal environment.

Bioerosion

Bioerosion encompasses the many d ifferent corrosive p rocesses by organisms.The m ost pervasive cau ses of degradation are b oring and grazing. Bioerosionerases i nformation from the fossil record , but it also leaves i dentiable t racesmade by organisms on remaining hard skeletons or s urfaces. Therefore, tracefossils p roduced by bioerosion add information on the d iversity of ancientassemblages.

Dissolution

Skeletal remains commonly are in equilibrium with surrounding waters, butchanges i n chemical conditions can cause s keletons t o dissolve. Dissolutionrepresents uctuation in temperature, pH or p CO2 in calcium carbonateskeletons. Siliceous skel etons al so can dissolve b ecause n ormal sea w ater i susually undersaturated with respect to silica.

Rounding

Broken ed ges of skeletons become rounded owing to dissolution and/orabrasion of exposed surfaces. Processes that control edge rounding probablyinclude a co mbination of dissolution, abrasion, and bioerosion. Rounding givesan estimate of time si nce break age.

Encrustation

The gr owth of hard skeleton substrates by other organisms is a commonoccurrence. Besides i ndicating exposure o f the skel eton above t he sed iment-water i nterface, encrustation can specify a p articular en vironment. Differentpatterns o f encrustation, as w ell as d ifferent biota, occur in differentenvironments.


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FragmentationBreakage o f skeletons i s u sually an indication of high energy resulting fromwave act ion or c urrent energy. Fragmentation also can be cau sed by otherorganisms t hrough either predation or scavenging.

Orientation

After death, skeletal remains ar e m oved by the t ransporting medium andoriented relative t o their h ydrodynamic p roperties. Fossil skeletons i n lifeposition indicate rap id burial, attachment to a rm substrate, or d eath of in-place i nfauna. Hard parts t end to orient long-axis p arallel to unidirectional owin current-dominated areas and perpendicular to wave crests on wave-dominated bottoms.

SizeAfter death and if not rapidly buried, a skel eton behaves as a s edimentaryparticle an d is m oved and sorted with respect to the car rying capacity of theow of currents, waves, or tides. Size ca n, therefore, be a n effective i ndicator ofow capacity in a h ydraulic or w ind-driven system.

From McRoberts (1998)

TAPHONOMY & PRESERVATIONFORMS OF PRESERVATION

UNALTERED

This form of preservation is r are in most of the geo logic column, but becomes m ore frequent inyounger s edimentary rocks. Types of unaltered preservation where even the sof t body parts ar epreserved include: (i) mummication, (ii) encasement in tar, (iii) encasement in amber, (iv)encasement in sediment, and (v) freezing. More f requently, however, only the h ard skeletal materialis p reserved after removal of soft body parts.


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Examples of unaltered preservation include t he skel eton of a h orseshoe cr ab, whose s hell iscomposed of interlocking plates an d jointed appendages w hich quickly disarticulate a fter d eath;cockle bivalved m olluscs, whose outer-most shell layer has been removed by ab rasion, yet the

original shell material of theinneransmonoid from the Cretaceous period inwhich you should note t he p early luster which is original aragonite sh ell material; and an insectencased in amber .

MOLDS & CASTS

This gen eral class o f preserv ation entails m aking "replicas" of the sk eletal hard parts of organisms. Ingeneral, a mold is an impression in the sed iment of a skel eton or shell. Once en cased in lithiedsediment, the d issolution of skeletal material leaves be hind the i mpression or mold of originalskeletal form. Thus, a m old is a "m irror i mage" of the o riginal skeleton. An internal mold (sometimescalled a st einkern) is t he i mpression of the i nside su rface of skeletal hard parts. An external mold isthe impression of the ou tside surface of skeleton or bo ne. An example of both types of molds can beseen in this i mage o f a t rilobite .

A cast is f ormed by the lling-in of a mold. It is t hus a t rue rep lica ( not a "m irror i mage") of the

original skeleton or s hell. By this d enition, the ca st one g ets f or a b roken limb is n ot really a cast atall but an external mold.

A graphical representation of the formation of casts an d molds i s provided in Figure 2 below.

Figure 2 - Different diagenetic p rocesses l eading to d ifferent preserva tional styles i nskeletal m aterials.

http://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/horseshoe.GIFhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/amber1a.GIFhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/inexmold.GIFhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/inexmold.GIFhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/amber1a.GIFhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/ammonoid.GIFhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/clams.GIFhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/horseshoe.GIF


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* Note t hat molds ar e p roduced directly a s imprints of the shel l and casts ar e p roduced from molds.


REPLACEMENT & RECRYSTALLIZATION

This common form of preservation involves chem ical and/or p hysical alteration or replacement oforiginal skeletal material. To properly identify replacement and recrystallization, one m ust knowwhat the o riginal constituents of the o rganism's s keleton were. These ar e p rovided in Figure1.3. Replacement occurs oft en by the lling in (by various m inerals) of the v oid space a fterdissolution of original skeletalmaterial. Sometimes, the rep lacement occurs o n a molecule b ymolecule ba sis. Common replacement minerals t hat you should be a ble to recognize i nclude Silica(SiO2) as s hown in the cor al, and Pyrite (FeS2) shown in the am monoid.

Recry stallization i nvolves t he physical re-arrangement of crystalline structure o f skeletal material.This i s a com mon phenomenon in shells w hich were o riginally aragonite an d/or c alcite (both formsof calcium carbonate- CaCO3). Examples, both of which are now calcite, include a gast ropod whichwas o riginally aragonite an d a b rachiopod which was o riginally calcite.

http://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/coral.GIFhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/gast%26brach.GIFhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/gast%26brach.GIFhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/pyrite.GIFhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/coral.GIF


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CARBONIZATION

As or ganic r emains d ecompose i n sediments, volatile con stituents s uch as oxyg en, hydrogen, andnitrogen are slowly lost to t he su rrounding sediments frequently leaving b ehind a car bon lm. Thisprocess is car bonization (or s ometimes cal led distillation), and occurs m ost frequently in oxygendecient, organic-rich environments s uch as basi nal black shales, and coal swamps. The car bon lmsoften show exquisite d etails of lants an d soft-body parts of an imals n ot r eadily preserved, and canoften be rec ognized by a d ark gray or bl ack lm with a m etallic sheen such as t hese f ern-like f ossilplants.

PERMINERALIZATION

Permineralization involves t he lling-in of pore an d/or void spaces i n shell or bone by secondarymineral matter i n solution. With permineralization, the t iny pore sp aces i n the f ossil are lled and theoriginal skeletal material is s till retained.However, it is o ften common for ot her t ypes o f preserva tion(e.g. replacement) to o ccur during a nd/or after permineralization. Because of its porous nature, boneand wood is especially prone to permineralization.

PROTISTA, EUBACTERIA, & PORIFERA

http://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/petrified.GIFhttp://paleo.cortland.edu/tutorial/Taphonomy%26Pres/Taph%26Pres%20Images/carbon.GIF


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From Stanley (1993)

Kingdoms EUBACTERIA and PROTISTA

Fossil organisms w ithin the Kingdom Protista represent the ea rliest life f orms kn own. Theseorganisms ar e ch aracterized by a si ngle-celled body plan and are con trasted to members ofthe Kingdom Eubacteria (green and blue-green algae) by having a n ucleus. This lab concentrates onthe p rotist phyla Foraminifera and Diatoms becau se m any of their constituents have m ineralizedskeletons an d an extensive fossil record. Because of their wide-spread distribution and rapidevolutionary rates, many of the protists are e xcellent index fossils u sed in biostratigraphic st udies.During this l ab you will become familiar w ith the m orphologic features an d be ab le t o identify eachof the g roups l isted below, in addition to knowing their geo logic ag es.

The recepatulitids ar e included here becau se they are no w believed to belong to the Chlorophyta o rgreen algae w ithin the s imply organized Kingdom Eubacteria even though they were once thoughtto be rel ated to sponges.


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CLASSIFICATION & GEOLOGIC RANGES

Kingdom Eubacteria (Precambrian - Recent)group " stromatolites " (Archaen - Recent)

Kingdom Protista (Precambrian - Recent)

group " receptaculitids " (Ordovician - Devonian) Phyl m Granuloreticulosa

Class Foraminifera (Cambrian - Recent) gro ! "fusulinids "(Late P aleozoic)

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

Phyl m Acrtinopoda

Class Radiolaria (Cambrian - Recent)

Phylum Chrysophyta

"diatoms " (Cretaceous - Recent)

Kingdom Eubacteria

"Stromatolites"

Stromatolites are organically produced sedimentary structures and are amongst the oldest fossilsknown on Earth (they occur in Archean rocks 3.5 b.y. old!). they are made by cyanobacteria (oftenerroneously called “blue-green algae”, however, because the cells are prokaryotic, they should notbe confused with true algae which are eukaryotes . Stomatolites are w ithout skeletons ( they arelayers of sediment), and differ from some similar-looking sp onges t hat have a m ineralized skelton.


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Kingdom Protista

"Receptaculitids"

Receptaculitids ar e a t ype of Dasycladacean green algae ( Phylum Chlorophyta). They arecharact erized by thick calcareous s heets, plates, or sometimes as b alls or d iscs that are p erforated bynumerous holes arranged in an o rderly (usually spiral) fashion. The holes are in fact externalmolds of the p lant's s oft stems an d not body fossils at all.

Class FORAMINIFERAForaminifera ar e the m ost common and geologically m ost important of the fossil protozoans. Thename t ranslates t o pore-bearing and refers t o the n umerous p erforations ( foramina) in the skel etonwalls. It is t hrough the foramina t hat the o rganism extends i ts p seudopod or protoplasm.

Today, nearly all forams l ive i n marine env ironments an d are either bottom dwellers ( benthonic ) oroat in the w ater column ( planktic ). Forams are characterized by multi-chambered tests which a re

built (singular = septum), whose ext erior exp ressions ar e t ermed sutures. Composition of the t ests ar eeither cal cite (C aCO3) o r ag glutinated (cemented foreign particles, e.g., sand or si lt grains).

The cl assication of Foraminifera i s b ased on (i) test microst ructure, (ii) test symmetry, and (iii)aperture type.

Test Composition and Microstructure

Agglutinated (sometimes called arenaceous). These tests ar e com posed of grains or fragments offoreign material cemented by the organism and commonly have a s ugary appearance.Occasionally g rains of quartz an d/or shell fragments can be seen.

Calcareous tests can ei ther be hyaline which can be distinguished by their glassy ap pearance or

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porcelainous w hich are u sually white o r opaque i n color and resembles c hina o r porcelain.

Test symmetry

1. Uniserial . Chambers are ad ded in a st raight or c urvilinear ser ies. (see Figure 1 below)

2. Biserial . Chambers ar e ad ded in an alternating fashion.

3. Triseri al . Chambers are add ed every 120 o in a sp iral fashion.

4. Planispiral . Chambers are ad ded around the p eriphery and are coi led in a si ngle p lane. Planispiraltests ar e evo lute w hen all previous chambers ar e v isible, and are i nvolute w hen only the l ast spiral orwhorl is v isible.

5. Trochospiral . Chambers ar e ad ded around the p eriphery, but each new chamber i s s lightly offsetso that a v ery low spire o r c one res ults. The cen tral part of the d isc on the si de o f the a perture i scalled the u mbilicus.

Fig re 1 - Foraminifera Test Morphology

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From #oardman et al (198$)

Ecology

During life, forams ar e ei ther ben thonic of planktic, relying on their pseudopodia for bothlocomotion and creating w ater currents for food gathering.

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

Planktic forams ar e r ecognized by their thin, and often perforated, tests an d globular i natedchambers. You should be able to recognize the difference between the two types of forams.

Larger Fo raminifera

Several times during the h istory of Foraminifera, tests m any times l arger than you have b een seenuntil now have ev olved. Although large t ests ar e k nown from several foraminiferal families, only two,the fusulinids (Family Fusulinidae) and nummulitids (Family Nummulitidae) are considered below.

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The nummulitids existed during the Early Cenozoic and are famous for their abundance inlimestones f rom which the G reat Pyramids of E gypt built. Their t ests ar e p lanispiral and involute,and unlike the fusulinids, are coiled around the sho rt axis. Examine this specimen from Egypt.

The fusulinids were i mportant benthic con stituents of Late Paleozoic shallow seas. The t ests offusulinids are nvolute a nd planispirally coiled about the l ong axis. The t est walls of f usulinids aremulti-layered in contrast to the m icrogranular t ests of other f orams. An individual fusulinid can beseen i n this i mage. A good example of a fusulinid limestone can b e seen in this image.

RADIOLARIA

Radiolarians are h eterotroph protozoans w hich thrive in the u pper layers of the seas . Theprotoplasm of radiolarians i s s urrounded by a t est commonly composed of an intricate l attice w ork ofopaline si lica ( there ar inor gro ups w hich construct their t ests o f strontium sulfate a silicaenriched with organic m aterial). Like t he foraminifera, radiolarians h ave p seudopodia w hichprotrude t hrough the p orous t ests t o aid in locomotion and food gathering. The t ests of radiolariansexhibit great morphologic d iversity, but they are t ypically charact erized by radial or sphericalsymmetry. Examine this microscope image.

Phylum CHRYSOPHYTA

"Diatoms"

Diatoms are a k ind of microscopic go lden-brown algae t hat secrete si liceous t ests ( sometimes cal led

frustules) consisting of two overlapping halves o r valves t hat t together. The w alls of the t ests are ornamented by pores, grooves, and ridges.

Diatoms occu r i n two basic forms: (i) the centric t ype i n which the t est has r adial symmetry, and (ii)the pennate type i n which the t est is el ongate an d has bi lateral symmetry. An example o f both typescan be se en in this m icroscope image.

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The centric type ar e p lanktic and predominantly m arine, whereas t he p ennate type ar e m ostly benthic

rock cal led diatomite, which is c omposed entirely of diatoms. Diatomite o ften forms by a d iatom

"bloom" in nutrient-rich fresh-water l akes.

PROTOCISTA, EUBACTERIA, & PORIFERA

PORIFERA & ARCHAEOCYATHA

Sponges, stromatoporoids, and archaeocyathids ar e i ncluded in this p art because i ndividualmembers w ithin each group share, at least partially, similar s keletal features an d symmetry leadingsome w orkers consider them all as bei ng members of the same p hylum. All are ben thic, sessile,suspension-feeders w hich inhabited a w ide va riety of exclusively marine env ironments t hroughoutmuch of the Phanerozoic.


Phylum Porifera

Class Demospongea (Cambrian - Recent

Class Hexactinellida (Cambrian - Recent)

Class Calcarea (Cambrian - Recent)

"Class Stromatoporoida " (Ordovician - ?Recent)

Phylum Archaeocyatha (Cambrian)


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Phylum PORIFERA

Fig re % - Basic Sponge Morphology


The p oriferans (sponges) are c haracterized by cell groups t hat are i ndependent of each other andhave the a bility to change t heir f unction during their l ife cycl e. The sk eletons o f sponges can becomposed of an organic substance called spongin (the stuff of an ordinary bath sponge), or t hey m ayhave cal careous or iliceous s keletonsomposed of chambers, or m ore c ommonly rod-like b ranchedelements cal led spicules. After d eath, spicules ar e scat tered across the se oor an d may be f ound asdisarticulated microfossils.

Large sp icules ( visible t o the u naided eye) are t ermed megalascleres, whereas sm all ones ar e cal ledmicroscleres. Spicules h ave f our ba sic sy mmetries: (i) monaxon, (ii) triaxon, (iii) tetraxon, and (iv)polyaxon. Examine Figure 2 b elow. Together the sp icular s ymmetry and mineral composition serveas t he p rimary basis in poriferan classication.

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Fig re % - Nomenclature of Common Megascleres & Microscleres in Fossil and ModernSponges

Modified from #oardman et al (198$)

Class Demospongea

Sponges w ith skeletons of spongin, spongin and siliceous s picules, or a skel eton of fused opalinesilica. When present, spicules are commonly m onaxon, tetraxon, or polyaxon, but never t riaxon. Hereis an example of a modern demosponge with spongin. Here is a good example of a fossildemosponge. Note in this specimen the canals in the siliceous walls.

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Class H exactinellida (previously Hyalospongae)

Sponges w ith siliceous s picules t hat are u sually triaxonscommonly fused to form a n et or box-like p attern. They are of ten called glass s ponges. For a recen t example o f a g lass s ponge, view thisimage. Compare it with Hydnoceras from the Devonian of New York.

Class Calcarea

Sponges t hat have calcareous sp icules as i n Astaeospongia ( the d isc s haped fossil in the f ollowingimage) or more com monly, non-spicular po rous chambers ( the o ther three f ossils i n the i mage).When spicules ar e p resent, they are n ot fused and are t ypically monaxons and /or tetraxons.

"Class St romatoporoida"

Although some t exts t reats t his gr oup as a m ember of the d emospongea, some p aleontologistsconsider stromatoporoids no t as t rue spo nges, but belonging to their own phylum. The m iddle r oadis t aken in this cou rse, treating the st romatoperoids as a arate cl ass w ithin the P orifera. The sh eet-like o r hemispherical skeletons of stromatoporoids ar e o f two types. The rst type h ave sm allmounds called mamelons from which canals called astorhizae radiate. This group has horizontalpartitions cal led laminae and vertical partitions cal led pillars.The s ace b etween the l aminae andpillars i s calledthealleyompare t he image with the accom panying gure b elow.

Fig re 3 - Stromatoporoid Morphology

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The secon d type o f stromatoporoid is s imilar t o the rst in having laminae a nd possibly pillars, yet itlacks t he a storhizae a nd mamelons. This f orm is q uite si milar t o algal stromatolites, but differ i npossessing a true calcareous skeleton.Smatoporoidssuchhee are quite common from theSilurian and Devonian shallow-water carbonates of central New York and also the C anadian Rockieswhere t hey often built reefs.

Phylum ARCHAEOCYATHA

The Archaeocyathids ar e p redominantly an Early Cambrian phylum with no living representatives.They g enerally have skel etons t hat formed a p orous calcareous cup or cone that resembles later

Paleozoic coral s. In fact, the a aeocyathids w here t he r eef builders of the Early-Middle C ambrian.The con e-shaped skeletons ar e com monly constructed of two perforate w alls s eparated by radiallyarranged vertical blades c alled septa. As shown in the accom panying gure, the skeletons ofarchaeocyathids come in two v arieties: (i) regulars that have b oth septa a nd tabulae b ut lackdissepiments ( small curved plates), and (ii) irregulars t hat lack septa, but have dissepiments an d rod-like b ars s imilar t o sponge sp icules. This si milarity has l ed some t o believe t hat archaeocyathids

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belong wit

Fig re & - Archaeocyathid Morphology


CNIDARIANS


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INTRODUCTION

The phylum Cnidaria (Coelenterata i n some t exts) includes bo th solitary and colonial organisms t hat

have rad ial and/or bilateral symmetry. Typical cnidarians al ternate each generation between a xedpolyp stage an d a free l iving m edusoid stage. Most cnidarians are considered carnivores becau se oftheir ab ility to actually catch food with their stinging cells ca led nematocysts. Some g roups,particularly the reef -corals em ploy photosynthetic al gae (zooxanthellae) within their t issues i n asymbiotic r elationship to aid in supplying food needed for their rapid growth.

The cn idarian classes Anthozoa (corals) and Hydrozoa h ave cal cied skeletons of aragonite an dcalcite a nd a g ood fossil record, whereas t he l ong fossil record of the cl ass Scyphozoa (jelly sh) iscomprised mostly of molds and casts. Class Octocorallia is n ot well represen ted in the f ossil record

because ounrelated anthozoans (e.g., some col onial Tabulates an d Scleractinians) because f orm represents a

basic and especially wave an d current energy).


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The rst part of the lab introduces you to the t axonomy of the Cnidarians an d their geologic ranges.The secon d part concentrates on aspects of coral morphology, coloniality, and integration that areused to deduce ancient environments


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 an thozoans are t he m ost important of the cn idarians becau se t heir polyps of tenproduce ca lcitized skeletons t hat are read ily preser ved as f ossils. They can be ei ther sol itary orcolonial. Common forms of anthozoans include cor als, sea-anemones, and sea-pens. Anthozoansdiffer from other Cnidaria in that they h ave n o m edusoid stage. They are exclusively marine an doccur at various depths from shallow to d eep water.


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Morphologic Terms (see accompanying gures)

Calyx : the b owl-shaped depression or " seat" in which the l iving polyp resides.

Corallite : the skeleton produced by one polyp, which m ay or may not be p art of a colony

Epitheca : the o utermost skeletal layer of a co rallite w hich sometimes s hows g rowth lines.

Tabula (plural tabulae): a h orizontal partition (or oor) dividing the co rallite sk eleton.

Septum (plural septa): vertical blade o r p artition within the ca lyx of a co rallite t hat are n ormallyradially arranged.

Dissepiment : small curved plate i n a co rallite n ear t he t abulae t hat is c onvex inward and upwards.

Mural pores : the sm all holes i n the ep itheca o f some t abulate co rals.

Columella : an axial rod in a co rallite u sually formed by the f usion of two or m ore sep ta t hat typicallyforms a t opographic p rominence i n the cen tral part of the cal yx.

Order TABULATA

The e xclusively colonial Tabulate co rals o ccur on ly in the P aleozoic. Their cal cite sk eletons t ypicallyhave a lateral wall (epitheca) that sep arates e ach rather sm all corallite. Each of the co rallites t ypicallyhave a t abula t hat serve a s t he oor f or t he p olyp. Septa i n tabulate co rals are e ther ab sent orinconspicuous. Although their grow th forms vary , they often occur i n "honeycomb" or chai n-likemorphologies.


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Figure 1 - Tabulate M orphology


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

Order RUGOSA

Figure 2 - Rugosan Morphology

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Figure 3 - Septal Growth Patterns


Order SCLERACTINIA

Scleract inian corals ( including all modern coral species) can be ei ther co lonial or solitary. Theiroriginally aragonitic ske letons h ave d issepiments, tabulae, and septa j ust as i n the P aleozoicrugosans. Although there are su percial similarities, scleractinian corals d iffer f rom rugosa co rals bytheir s keletal mineralogy and by their m ethod of septal insertion during growth. Scleractinian coralsalso h ave six p rimary septa, but in contrast to rugosa coral s, subsequent septa a re ad ded in all six o fthe resu lting spaces. An important distinction between the t wo orders i s t hat for t he S cleractinia thesepta are nserted between every t wo p re-existing septa i n later growth stages. Good examplesshowing corallites and sep tal arrangement in a colonial form can beeen in thisspecimen. Seealso the colonials - - - noting the d ifferent growth morphologies. This

specimen is a so litary coral collected from deep water; note i ts s imilarity to some o f the so litaryrugosans seen earlier.

Subclass OCTOCORALLIA

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Although octocorals ar e ver y abundant in modern oceans, they d o not have a g ood fossil record at all because o

sea fans such as shown by these specimens. - - Other groups of octocorals have even a

poorer f ossil record because t hey have only calcitic sp icules o r n on-calcied skeletons. One o f thelatter gro up are t he sea-p ens w hich have so ft, feather-like sk eletons.

Class HYDROZOA

Hydrozoans are a d iverse g roup of cnidarians t hat inhabit a va riety of marine an d fresh-waterenvironments. The m ore important groups (in terms of paleontology) construct their skeletons ofcalcite. These cr itterssometimes su percially resemble co rals i n skeletal morphology and growthhabits, or they can also o ccur as en crusting sheets or ect blades.Some h ydrozoa su ch as t he recoral Millipora h ave t hick calcareous l amellar skel etons w ith vertical tubes an d cross partitions.

Class SCYPHOZOA

Scyphozoa (jelly sh) only occur in marine env ironments. The ar e typied by a r educed polyp stageand an extended free-swimming medusae s tage. As on e m ight imagine, fossil scyphozoans are rarelypreserved as f ossils; yet surprisingly they are robably represented in the famous Ediacara f auna o fthe Precambrian. Almost all fossil remains of scyphozoans occ ur as m olds and less commonly casts.Some w orkers w ould place t he Conularia as a Su bclass of the Scyp hozoa.

CNIDARIANS

PALEOECOLOGY

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Colonial coral growth habits an d integration levels

The m orphology of coral colonies c an be g rouped into three b road categories: (i) encrusting formswhich are of ten sheet-like su ch as t his s pecimen. (ii) massive forms which are domal orhemispherical such as in sp ecimen. (iii) erect forms which ar e branching or palmate such as thisspecimen You sho uld return to the coral specimens in the rst part of the lab making sure youcan p lace eac h into one of the three m orphologic gr oups.

Colonial corals n early always sh ow some l evel of integration between individual coralites. Suchintegration is u sually reected in the co ral's ske eton by the d egree o f spetal sharing ranging fromcompletely isolated corallites t o those w here individual corallite cannot be recognized.

Figure 4 - Colonial Cnidarian Integration Types

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You should return to the sp ecimens of the ear lier part of the l ab and make su re yo u can identify theintegration types d epicted in Figure ab ove. You should nd, for example, that this s pecimen, iscateniform, this specimen, is cerioid, and this specimen, is m eanderoid.

It is i mportant to know that different integration levels w ere d ominant during different periods ofgeologic t ime. In fact, given a l arge enough sample, a rou gh estimate o f gelogic ag e can be o btainedon the rel ative p roportions o f various i ntegration levels.

Paleoenvironments

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Corals occur as ramework organisms i n reef environments an d as i mportant constituents i n level- bottom communities.

uctuating sea l evel, turbidity, and salinity. Of all of these f actors which may result in differing

growth morphology, the ov erall shape o f coral colonies i s m ost responsive t o water (= wave +current) energy. However, it should be n oted that the m orphologic r esponse i s qu ite d ifferent when acoral is i n a ree f setting or i n a l evel bottom setting.


Although quite d iverse i n large-scale m orphology and facies r elations, reef systems gen erallyconform to the scheme d epicted in the acc ompanying gure . Note that the reef proper (the or ganic

build-up) degree o f branching in colonial corals c an generally be corr elated with water energy. Thus h ighenergy often results in erect, branching and palmate forms, whereas l ower water energy levels ar egenerally si tes where the encr usting and/or m assive forms predominate.

The o pposite i s gen erally true for level-bottom settings s uch as i s of ten found in the D evonian ofcentral New York. Here, greater water energy u sually res ults in encrusting and/or massivemorphologies. This i s in contrast to lower water energy level bottom environments w here b ranching

and ramose m orphologies ( albeit more d elicate t han in reefs) predominate.

BRYOZOANS


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INTRODUCTION

The Bryozoa (moss ani mals) are a geo logically important group of small animals; some t hatsupercially resemble cor als. All bryozoans are colonial and most are marine. Bryozoans are mostabundant in temperate-tropical waters t hat are n ot too turbid. They require a h ard or rm substrateon to which the at tach to or encrust, and clear agi tated water from which they obtain theirsuspended food.

Enclosed within a skel eton of c alcite, bryozoans h ave a sac-like coelomate b ody with a w ell denedmouth, anus, and other specialized organs. One su ch organ is t he l ophophore ( a ci liated structureused in food gathering) that is at tached to tentacles t hat surround the m outh (see Figure 1 below).The lophophore i s a s tructure shar ed by the p hylum Brachiopoda l eading some to construct thePhylum (or Superphylum) Lophophorata to include both brachiopods and bryozoans. Theclassication follows yo ur t ext in treating the Bryozoa a nd Brachiopoda a s s eparate p hyla.

Figure 1 - Section of a Bryozoan Feeding Zooid


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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 (J urassic-Recent)


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GENERAL MORPHOLOGY AND ECOLOGY

Morphologic Terms (see Figures 1 & 2 )

Zooid : Individual animal or m ember in a bryozo an colony.

Zooaria : The col ony of bryozoan animals.

Zooecia (Zooecium singular): Living chambers constructed by a col ony of zooids. The zo oecium isthe l iving chamber constructed by one individual.

Autopore : Zooecium for the f eeding zooid called autozooid which is u sually the l argest of thevarious zo oecia.

Ancestrula : The an cestral founding zooecium from which o ther zooecia in the col ony bud.

Diaphragm : A partition in a t ubular zo oecium, transverse t o tube l ength similar t o the t abulae insome corals.

Aperture : The op ening through which t he living animal could extend from its zooecium.

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

Frontal : In zooecia w ith considerable w all area ex posed at the co lony surface, a f rontal is t he ex posedpart of any one zooecium.


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Immature and Mature regions : In trepostome b ryozoans, the d istal or last formed (most recentlygrown) end of a zoo ecium has close-spaced diaphragms and is called the immature ar ea. Theproximal end (oldest part) of the zoo ecium has few diaphragms and is called the m ature region.

Figure 2 - Section of a Colonial Bryozoan Zooecia


General Morphology and Ecology


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As bryozoan individuals are qu ite small, they ar e commonly observed under the microscope fromlongitudinal or t ransverse t hin-sections. A longitudinal orientation is p arallel to zooecium wall,whereas a transverse sect ion is p erpendicular t o apertural face.

Bryozoans come in a va riety of colonial growth habits that can easily be ob served without thin-sections. Like corals,thegowthhabitofas- massiveor domal, or erect. - Generally speaking, byozoan growth-habits are a function of waterenergy similar to co rals which l ived in level-bottom communities; encrusting and massive forms ar efound in high-energy environments w hereas d elicate b ranching and erect forms l ived in quiteenvironments.

BRYOZOANS

CLASSIFICATION

General Information

Division of bryozoan groups i s b ased on surcial morphology, extra-zooidal structures, colonialgrowth habits, zooid morphology, presence of specialized zooids (e.g., maternal zooids), and internalstructures of the zo oecium. In order to help in identication, it may help to know that colonial

bryozoans cme

1. Those w ith tightly p acked zooecia w hich sh are zoo ecium walls, they h ave m ultiple p ores and awell dened mature an d immature region such as i n the trepostomes, cyclostomes, and thefenestrates.

2. Those w ith moderately to loosely packed zooecia u sually encrusting one-zooecium-thick, andcommonly with frontal walls as typied by the Cheilostomes

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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 (J urassic-Recent)

Order TREPOSTOMATA

Trepostomes ar e cha racterized by long-curved zooecia sep arated by thin walls. Each zooecium hasmature an d immature regions. Apertures of autopores are typically p olygonal. Trepostomes can b edifferentiated from similar-looking cryptostomes by the t hinner walls bet ween their zoo ecia. Thespecimens are erect forms, whereas these specimens are massive.

Order CYCLOSTOMATA

Cyclostomes ar e ch aracterized by zooecia t hat are s imple t ubes w hich lack partitions (diaphragms)and have rounded apertures. and well dened mature and immature regions. Most cyclostomes areencrusting forms such as the example provided. , and some, like this small gured speci menencrusting a D evonian nautiloid cephalopod, can be q uite sm all and very l oosly arranged creeping

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zooecia.

Order FENESTRATA

Fenestrates ar e cha racterized by theirzooariam orphology which f orm a m esh or n et-like shape w ithzooecia-bearing rods an d open window-like regi ons c alled fenstrules. Most fenestrates h ave

considerable ex tra-zooid skeleton material which is necessary f or support. This or der is t ypied byerect, delicate m orphology such a s those seen i n these specimens. Note, however, that somefenestrates h ave considerable ex tra-zooidal material such Archimedes w hich is an axial rod thatsupports t he n et-like z ooecia.

Order CHEILOSTOMATA

Cheilostomes ar e cha racterized by their loosely packed colonies of box o r coffin-shaped zooecium.Many have round apertures and large frontal areas on which brood pouches which house thematernal zooids can o ften b e ob served. .

CEPHALOPODA, GASTROPODA

& other Molluscs

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INTRODUCTION

Molluscs ar e g reatly varied in both morphology and life h abits. They include familiar l iving formssuch as cl ams, snails, the o ctopus, and squids. Several groups h ave g reat economic importance s uchas oysters and the blue mussels, and some gr oups such as garden slugs and the zebr a m ussel can b e

bothersome pesof which t he cephalopods and gastropods are geo logically the m ost important.

Most molluscs are m obile m arine cr eatures, although some h ave i nvaded terrestrial environments.Molluscs have a n external shell (single o r bivalved) enclosing the m antle an d visceral mass, amuscular foot which ai ds in attachment and/or l ocomotion, and a radula. The radula is not knownfrom the b ivalves ( a g roup covered in the n ext lab), but is presumed to have b een primitive i n the

bivalve


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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


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The organ system of monoplacophorans are ar ranged in a series and are segmented (orpseudosegmented) leaving paired muscle scar s on the sh ell interior. Some i nvestigators su ggest thata P aleozoic an d early Mesozoic g roup called the S ome f ossils t ypically classed as b ellerophons ( here

treated as gas tropods), may h ave an untorted body plan. This has been deduced from thearrangement of muscle sc ars on the i nterior of the u nivalve bellerophons. Most other bellerophons,however, do exhibit torsion and should rightly be cl assied as t rue g astropods. Apart from the

bellspecimens.

Class AMPHINEURA

Amphineura (Polyplacophora of some texts and commonly re ferred to as t he Chitons) arecharacterized by an elongated body with a h ead and bilateral symmetry. Polyplacophorans p ossess aradula. The soft bodies of polyplacophorans are surrounded by a m uscular mantle g irdle (cuticle)which h as ar agonitic spicules. Above the m antle cu ticle, polyplacophorans have a d orsal shell madeup of eight articulated plates or valves.Some r ecent examples of polyplacophorans are p rovidedhere.

Class SCHAPHOPODA

Scaphopods (commonly called tusk sh ells for obvious r easons) are a r elatively minor class of marinemolluscs. They can actively trap food particles w ithin the sed iment by use o f their s pecializedtentacles. Scaphopods ar e ch aracterized by a sm all univalved shell that is op en at both ends. Thelarger an terior en d is perm anently embedded in the sed iment. The sm aller posterior end is op ensnear t he sed iment-water interface. See t he exa mples of Recent and fossil Dentalium.

GASTROPODS

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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 su ch com mon forms such as s nails, slugs, and whelks, occupy both marineand non-marine env ironments. Although many gastropods ar e h erbivorous grazers, several groupsare act ive ca rnivores ab le t o drill through the sk eleton of the l uckless v ictim.

Most of the g astropods are cl assied on the ch aracteristics t he g ill structures an d other sof t-bodiedfeatures. Few distinguishing characters of the u nivalved shell are u sed in classication as m any arethe r esult of convergent evolution. Although the d ifferences in the shel l form may b e d ifficult torecognize, different morphologic g roups can generally can be d ifferentiated on characteristics ofornamentation, shell shape, and ap erture. The shell of many gastropods can ei ther be external or,less commonly, internal. The difference can of ten be d educed by t he luster of shell material andthe p resence o f other f eatures su ch as d eviations o f a st ructural shell form.

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Gastropods ar e r adulate o rganisms w ith a t orted body (e.g., the b ody is r otated 180û so t hat the an usis abo ve t he h ead. Gastropods t ypically have a helical coiled univalved shell whose op ening(aperture) may b e closed by an operculum. Another f eature w hich is u seful in discriminating

among groups i s t he s tructure cal led the sel enizone w hich can be exp ressed as ei ther a ser ies of holesas in Haliotis, or as a groove along the periphery which is often seen as a sharp b end in thegrowth lines o f the sh ell. Other features s uch a s ribs or the siphonal canal may a lso b e important.

Although the sha pe o f gastropods can be d escribed in terms s uch as " high-spired", "low-spired", or"cap-shaped", many of the sh ape ch aracteristics c an easily be d escribed mathematically by fourparameters S, W, T, and D.

Figure 1 - Gastropod Coiling Parameters

Where:

S sha!e of generating c r'e (loosely defined as the ratio bet een a!erat re height and idth)

distance of generating c r'e from the a is of rotation

W rate of e !ansion of generating c r'e

T rate of translation along the coiling a is

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Subclass P rosbranchia

The d istinguishing shell feature a mong prosobranch gastropods i s t hat they are al l either c ap-shapedor t hey are h elically coiled.

Order Archaeogastropoda . Many archaeogastropods have an identiable selenizone (except forsome t rochids) in addition to an operculum. The shel l of archaeogastropods can be ei ther internal orexternal. This group is exclusivelymarine.Most areturbinoform, but others may be highspired, cap-like as in recen t limpets, or ot her s hapes. Many of t he cap -like archaeogastropodshave a sm all hole in the ap ex o f the cap which is a m odied selenizone. The se lenizone of otherspecies of archaeogastropods m ay be a series of ho les s uch as i n Haliotis. As m entioned earlier,the g roup of involute u nivalves w ith a sel enizone cal led bellerophons, (especially those w ithunpaired muscle sc ars), may b e r egarded as A rchaeogastropods. Examples of bellerophons ar eprovided.

Order Mesogastropoda Mesogastropods do n ot have a sel enizone. Their shell can be ei ther

internal, which commonly have a slit like aperture, or external, in which round or ovidapertures are common, some of which h ave a l ip. A very common group includes the turritellids, a h igh-spired group typical of post-Jurassic.Another common example of mesogastropods are theslipper sh ells, belonging to the genus Crepidula. Other forms, such as the Vermicularia, often beco me uncoiled (or vary coiling parameters) during ontogeny. Of specialnote is the com mon low spired Polynices, who is an active carni vore w ho d rilled holes i n the shel ls ofother m olluscs.

Order Neogastropoda Neogastropods d o n ot posses a s elenizone, yet they typically have asiphonal notch or c anal and elongated and non-circular, and commonly slit-like, apertures. Typicalexamples of this gr oup occur in the common whelks an d others w ith strong ornamentation. -Although other forms such as Conus are also quite common.

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Subclass Pulmonata

Pulmonates can have a n external or i nternal shell, or t he sh ell may be a bsent (e.g. terrestrial slugs).Many pulmonates ar e t errestrial or l ive in lacustrine en vironments. The p ulmonates c an typically berecognized by their often thin shells an d distinct shell morphology which is t ypically conispiral andrather bulbous. Furthermore, many pulmonates have a well dened ap erture lip as in Helix. Hereare sever al other exam ples.

Subclass O pisthobranchia

Most Opisthobranch g astropods ar e m arine p lankton and lack a m ineralized skeleton. Members t hatdo have a sk eleton, including the p teropoda, are u sually small and either c one-like o r vari able sh aped

because laboratory

CEPHALOPODS



Class Cephalopoda (Cambrian-Recent)

Subclass Coleoidea (Devonian-Recent)

Subclass Nautiloidea (Cambrian-Recent)

Subclass Ammonoidea (Devonian-Cretaceous)

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Class CEPHALOPODA

The cep halopods are a cl ass of mobile m ollusks, most of which a re n ektic or nekto-benthic.Cephalopods have a bi laterally symmetrical body, a p rominent head, and a m odied foot in the formof tentacles. Although during t he Pa leozoic and Mesozoic, cephalopods achieved great diversity andabundance in marine h abitats, only two genera p ossessing skeletons ar e kn own today. See t heexample of a Nautilus. Supercially the shell or conch of cephalopods resemble gastropods;however, most cephalopods coil in a p lane, whereas ga stropods ar e h elicoiled. Furthermore, incephalopods w ith an external conch, the coi led shell is chambered.

Cephalopod Morphology

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

Phragmocone or conch: the ext ernal chambered shell.

Septum (plural septa): an internal partition which separates t he ch ambers.

Living chamber : the sp ace bet ween the ap erture an d the last septum.

Siphuncle : the t ube con necting the l iving chamber with all previous chambers. The si phuncle is t heplane o f bilateral symmetry. See t he exa mple o f the si phuncle o n the Recent Nautilus.

Suture : the o uter edge of the sept um (or juncture o f septum with shell wall) which usually isexpressed i n outer wall of shell. The suture can b e relatively st raightasinautilus or uted withsaddles and lobes, saddles ar e con vex toward the d irection of growth whereas l obes ar e con cave.(See gure under subclass Ammonoidea).

Ribs : thickenings o f external shell that may not be co incident with sutures.

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Keel : thickening along the o uter (venter) margin.

Shape o f External Shells

Several different shapes are common among fossil and extinct cephalopods. These include ort hoconicor straight, brevicone, evolute p lanispiral, involute p lanispiral, or heteromorphic.

Morphology of I nternal Shells

By denition, internal shells w ere su rrounded by esh during their d evelopment. Thus, they arecommonly solid plates or n early solid. Some t erms t hat apply to internal shells i nclude t hephragmocone - the con ical cavity in the an terior end of a b elemnoid; and the rostrum - the p art of a

belemnoid encl The ro strum is sol id calcitecomposed of radially arranged bers exh ibiting concentric grow th bands.

Nonskeletal hardparts

A variety of non skeletal hard parts m ay b e ass ociated with cephalopods including Aptychi, whichmay serve as an o perculum. Cephalopods m ay also have a beak an d radula to aid in obtainingfood.

Subclass COLEOIDEA

The C oleoids ar e p erhaps t he m ost familiar c ephalopod mollusks i ncluding as t hey do the o ctopodsand squids. Coleoids ar e ch aracterized either by an internal skeleton or by lacking a sk eletonaltogether. The i nternal shell of coleoids i s al most exclusively straight (=orthoconic), although a f ew

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groups have a coiled sh ell. Others have a more complicated p attern su ch as in the cuttlebone. Theinternal skeleton may co nsist of two parts, the o uter rostrum and inner phragmocone as t ypied inthe b elemenites an o rder of squid-like an imals w hich p roduced cigar s haped rostrum which h as a

conical depression at one en d and a cent ral cone-like p hragmocone w hich i s r arely found.

Subclass NAUTILOIDEA

As with the am monoids (see bel ow), the nautiliods are an important group of cephalopods with anexternal shell. However, unlike t he am monoids, the n autiloids hav e l iving representatives in thegenus Nautilus. Nautiloid sh ells are external and are characterized by either straight or slightlywavy su tures. Nautiloid sh ells are either orthoconic, or they are coiled, such as the RecentNautilus; see al so t he fossil examples. The si phuncle m ay be sm all or l arge, but is t ypicallycentrally located .

Subclass AMMONOIDEA

This is a ve ry important extinct group of cephalopods which i ncludes all forms with an external shellwith uted septa. Most are p lanispiral, but some m ay b e h eteromorphic (= not planispiral which caninclude o rthoconic o r a v ariety of shapes). The si phuncles are ge nerally small and ventral in position.Division within the am monoids i s bas ed upon the g rades of suture uting. There ar e t hree g radesyou will need to know which a re i llustrated and described below:

Figure 2 - Ammonoid Suture Patterns

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Goniatite su ture . Saddles an d lobes ar e p resent. The g oniatite su ture i s cha racterized by undividedrounded saddles and undivided angular lobes. Ammonoids with this type of suture ar e calledgoniatites.

Ceratite suture . Saddles are u ndivided whereas the lobes are d ivided. Ammonoids w ith this type ofsuture a re ca lled cera tites.

Ammonite suture . Both the saddles and lobes ar e d ivided. Ammonoids with this type of suture ar ecalled ammonites. Although many of the am monites are coiled, there ar e many genera such asBaculites, which is heteromorphic and encompasses a variety of coiling shapes.

BIVALVIA

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INTRODUCTION

This laboratory discusses t wo cl asses of molluscs: the b ivalves an d rostroconchs; of which the bivalve

long-ranging for precise s tratigraphic corr elation and zonation, their morphologic at tributes are verydiagnostic o f their d iverse l ife-habits an d paleoecology. As s uch, this l aboratory d eals w ith aminimum of classication (only to cl ass level) and concentrates more on paleoecology.

Like other molluscs, these t wo classes have a eshy mantle en casing the v isceral mass and amuscular f oot. Unlike g astropods an d cephalopods, bivalves secr ete t wo shells r ather t han one.Additionally, bivalves h ave l ost the r adula, which is p resumed to be a primitive feature am ong allmollusks. The R ostroconchs are si milar i n many regards t o bivalves, especially in their hy pothesizedsoft parts, a si gnicant difference i s t hat the sh ell is p seudobivalved.


Phylum Mollusca


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Class Rostroconchia (Cambrian-Permian)

Class Bivalvia (Cambrian-Recent)

Subclass Paleotaxodonta

Subclass Isolibranchia

Subclass Pteriomorphia

Subclass H erteroconchia

Subclass Anomaldesmata

Class ROSTROCONCHIA

Rostrochonchs ar e a r elatively m inor Paleozoic group which m ay h ave an i mportant phylogeneticposition within the p hylum Mollusca. Some au thors suggest that rostroconchs evol ved from an early

monoplacophoran ancestor an d gave ri se t o both bivalves and scaphopods, leaving the ceph alopodsand gastropods as descendants f rom a se parate m onoplacophoran stock.

Although they m ay h ave an internal anatomy si milar to b ivalves, rostroconchs are characterized by asingle, pseudobivalved shell which encloses the m antle an d muscular f oot. The an terior p art of shellhas a gap e from which the foot could probably em erge an d an elongated tube on the posterior endcalled the r ostrum which m ay h ave ai ded in water ltration. Although only one exam ple i s provi dedfrom the laboratory, please examine the illustration below.

Figure 1 - General Rostrochonch Morphology

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Class BIVALVIA

Bivalves, sometimes cal led Pelecypods ( meaning axe foot) or, in older l iterature, referred to asLamellibranchs, are a v ery diverse and abundant group of molluscs w hich inhabit a v ariety ofmarine an d non-marine env ironments. Their long geologic hi story an d variety of forms have m adethem the p opular subjects of many evolutionary and functional morphological studies.

For those w ho work on modern bivalves, often the ch aracters s uch as t he g ill structure an d even colorpatterns hav e t aken prominence i n classication. However, for those w orking on only the p reserved

hard parts o f fossils, usually features su ch as d ifferences i n teeth provide the cl assication scheme.Unfortunately, because bi valves h ave m any morphologic features with adaptive v alue, many of thesefeatures h ave a risen more t han once. As a resu lt, it is o ften difficult to erect a cl assication thatreects an evolutionary h istory. The cl assication scheme g iven above (which you are no t responsiblefor) is d erived in part from your t ext and is an attempt to incorporate b oth hard and soft partmorphology.

The sh ell of bivalve molluscs is characterized by two calcareou s h alves, called valves, which can becomposed 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 o utermost layer ofthe b ivalve shell, called the p eriostracum, is composed of a h orny organic substance w hich in theexample i s t he d arker m aterial only on the ex ternal part of the sh ell.

The b eak is located in the d orsal region of bivalves. The by ssus or foot protrudes f rom the an terior of

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the sh ell, while t he p osterior t he sh ell is t he reg ion of siphon protrusion (at l east in some b ivalves).The p lane bet ween the two valves ( or c ommissural plane) is the p lane of symmetry which separ atesthe left from right valve. Note t here i s no t an upper and lower valve ( as i n brachiopods) because m ost

bivalvemost bivalves, the sy mmetry is s econdarily lost in others. Note t hat in one o f the sp ecimens, thereis close t o a p lane of symmetry within the va lves. This asymmetry co rresponds to the living habitof the b easts, and those w ho have lost their ori ginal bilateral symmetry between the v alvescommonly live w ith their plane of commisure not perpendicular to the sediment surface.

Left or right valves c an be d etermined by viewing the p osterior end (as s hown in the gure bel ow).

Figure 2 - Determination of Left and Right Valve

The t wo halves o f the b ivalve shell are u sually joined at the d orsal margin by a l igament which acts asa sp ring. The l igament may be i nternal, as i n oysters, mussels, or scallops. Some i nternal ones con sist

of horizontal or vert ical bands w hich sit in grooves. Other ligaments m ay b e ext ernal. Thehinge margin may also b e o ccupied by a ser ies o f teeth and sockets col lectively referred to asdentition (see bel ow). The o pening and closing of the shel l are c ontrolled by adductor muscles(which oppose t he f orce o f the l igament) that often leave p hysical scars o n the v alve i nterior ( see

below). tshell, in addition to smaller on es t hat control the si phons, foot, and/or by ssus. General terms t hat

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you will need to know are g iven in the n ext section.

MORPHOLOGY

General Morphology

Beak : The reg ion of initial growth of shell. The b eak can be cu rved to either t he a nterior or, less

commonly, the p osterior. The g eneral region of the b eak is of ten called the u mbone.

Auricle : A wing-like p rotrusion along the d orsal margin, this can be ei ther anterior and/or posteriorof the b eak. See the w ing-like p rojection in the ex amples.

Byssal notch : Anterior depression below the au ricle from which the by ssal threads em erge. Such anotch can be v iewed directly beneath the an terior auricle in this exam ple.

Escutcheon : A small curved area o n the d orsal margin posterior t o the b eak. Both valves m ust be joined

Lunule : A small curved area o n the d orsal margin anterior t o the b eak.

Equivalved : Both valves b eing equal in size an d shape.

Inequivalved : Two valves of unequal size an d shape.

Equilateral : An individual valve that is s ymmetrical along its m id-line as i n most brachiopods.

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Inequilateral : Valves t hat are n ot symmetrical along their m id-line a s i s t he case f or m ost bivalvespecies.

Dentition and Ligaments

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

Lateral teeth : The t eeth extending laterally from the b eak.

Edentulous s pace : Hinge reg ion lacking teeth, usually present between the card inal and lateral teeth.

Resil ifer : A small depression along the h inge plate w hich holds an internal ligament; may b e a si nglepit or co nsist of multiple p its.

Taxodont dentition : A series o f small parallel to sub parallel teeth which are p erpendicular t o hingeline.

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

Desmodont dentition : having an internal ligament and a ch ondrophore, but usually lacking w elldened teeth.

Schizodont dentition : having prominent bifurcating or d iverging teeth.

Figure 3 - Bivalve D entition


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Musculature

Pallial line : Line o f mantle at tachment (see Figure 4 below).

Pallial sinus : An indentation in the p osterior part of the p allial line w here t he si phons c an be

retracted.

Dimyrian : A valve h aving two adductor m uscle sc ars; one an terior and one p osterior.

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

Anisomyrian : Dimyrian shell where t he t wo adductors ar e o f unequal size; usually the p osterior scar

is t he l arger o f the t wo.

Monomyrian : A shell having only one ad ductor scar; which is u sually a cen trally positionedposterior ad ductor s car.

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Figure 4 - Interior Shell Markings

Feeding

Most bivalves are lter f eeders, trapping suspended food particles as w ater p asses through their gi lls.Only two g roups, the nuculoids and cryptodonts, actively feed on organic material within thesediment and are t hus t rue d eposit feeders. Taxodont dentition is ch aracteristic o f deposit feeders.

Relations t o Substrate

Bivalves h ave a variety of morphologic f eatures t hat can be rel ated to their p articular l ife h abit ormode o f attachment to the su bstrate. We w ill examine se veral.

Infaunal

• Burrowing : Shells ar e u sually equivalved and isomyrian (or anisomyrian) with a d istinctpallial line. They include: the n uculoid burrowing deposit feeders, the sh allow burrowingnon-siphonate forms l acking a p allial sinus, and deep burrowing siphonate forms i dentied

by a distinct pall


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• Boring : Shells are u sually thick, equivalved, and cylindrical in cross section. Some f orms aremoderately ornamented with ridges and stout spines whereas others such as the "shipworms" are t ubular in form.

Semi Infaunal

• Byssally attached (endobyssate) . Similar t o many epifaunal byssate f orms ( see b elow), yetmaximum shell width (ination) is at mid-line of shell cross-section. Some forms can beelongated an d fan-like with a reduced an terior area. Examples include pen shells, and themussel-like modiolids, and som e ark shells. The depth to which the bivalves are partially

buried can often be deduced by

themselves ab ove the sediment-water interface.

Epifaunal

• Byssally attached (epibyssate) . Shells can be ei ther equivalved or inequivalved depending ontheir o rientation to substrate d uring life. Usually, all epibyssate f orms h ave a reduced anteriorregion. Some g roups, such as t he b lue m ussels, are si milar t o endobyssate forms exc ept themaximum ination is below the m id-line of the val ves c ross-section. Other forms may h ave a

byssal notch and/or a well along the v entral margin.

• Reclining . Shells ar e co mmonly inequivalved with a l arger l ower ( usually the l eft) valve whichis more inated or convex while t he u pper valve m ay b e p lanar. Some al so exh ibit spines,especially on the l ower v alve, to aid in stabilization in soft substrates i n a m anner si milar t osome br achiopods. Many have a sm all attachment area at beak where ear liest growth stageswere cemented. The giant clam Tridacna, who has photosymbionts similar tohermatypic scl eractinian corals, is a recliner even though it had a functional byssus d uring itsearliest j uvenile st ages.

• Swimming . Shells are u sually equilateral but not equivalved. The l ower ( usually the l eft) valveis usu ally slightly larger. Swimming forms ar e t ypied by having a g reater umbonal angle(greater t han 105°) than similar-looking epibyssate f orms. Furthermore, swimming formstypically have a single (monomyrian), large, centrally located adductor muscle.

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• Cementing . Shells are c ommonly inequivalved with the lower (usually left) valve a ssumingthe form of the o bject to w hich it is cementing, a con dition called xenomorphism. In suchcases, both valves are u sually highly variable i n shape, as i n the co mmon oysters and otherforms as well. Some groups such as the Cretaceous rudists could reac h very l arge sizesand were abl e to form reefs mimicking cor als in both morphology an d ecology.

ECHINODERMATA


INTRODUCTION

The ph ylum Echinodermata consists of several types of complex organisms which show a gen eralpentameral symmetry an d have a well developed water vascular system. Echinoderms are alsocharacterized by their m esodermal skeleton. Echinoderms occu r in a v ariety of morphologiesincluding free-living forms s uch as st arsh and sand dollars as w ell stalked forms s uch as sea l ilieswhich are at tached to the se a oor.

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The rst part of the l ab will concentrate o n the st alked echinoderms al so cal led pelmatozoans.Pelmatozoans are excl usively marine a nd live i n a v ariety of habitats of no rmal salinity. They are al llter-feeders. As a g roup, the p elmatozoans h ave b een quite ab undant in the g eologic p ast especially

the Paleozoic, yet since t he cl ose of the M esozoic t hey have m ainly relegated to deep-water, crypticenvironments.

The second part of this lab will concentrate on the very d iverse n on-stalked echinoderms belongingto t he su bphyla A sterozoa an d Echinozoa, and collectively referred to a s free-living echinoderms.Similar t o the p elmatozoans, the f ree-living echinoderms al l have a mesodermal skeleton comprisedof calcite p lates an d a co mplex w ater-vascular s ystem including tube-feed. Unlike t he p elmatozoans,the grou ps of this lab a re qu ite abu ndant in the m odern seas, occupying a l arge n umberenvironments by an equally large number of life-habits. Because of their abu ndance an d diversity, theechinozoans w ill be t he l argest part of the l ab.

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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 A sterozoa (Ordovician-Recent)

Class Asteroidea (Ordovician - Recent)

Class Ophiuroidea (Ordovician - Recent)

Subphylum Echinozoa (Precambrian?, Camb-Rec.)

Class Echinoidea (Ordovician - Recent)


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Class Edioasteroidea (Cambrian-Carboniferous)

PELMATOZOAN GENERAL MORPHOLOGY

In general, the p elmatozoan skeleton can be d ived into two m ain parts: The stem and the cal yx. Thestalk or s tem is composed of numerous d isks called columnals which have a central hole cal ledthe lumen. Stems are often sec ured to the substrate by means of a holdfast or root system. Thecalyx (sometimes called theca), a cup-like structureawn inhesesecmens, which may ormay n ot support a var iety of arms. As ou tlined below, the calyx is usually composed of a n umberof different kinds of plates, grooves, and pores; some o f which are qu ite sp ecialized

Appendage and Calyx Morphology

Ambulacral groove : one o f the 5 radially arranged regions s pecialized for f ood gathering

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