Fossil Guide
BEGINNER'S GUIDE FOR IDENTIFYING COMMON INVERTEBRATE FOSSILS
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By Sarah Leibson, Paleobiology 2001
Professor Buchwald
Introduction:
This guide aids the identification and understanding of common fossils in eight invertebrate phyla. By answering questions about a specific a fossil specimen, you can identify the specimen's phylum. Depending on the specimen you can also identify its class within the phylum. This guide also provides basic information on commonly fossilized organisms including feeding style, locomotion, reproduction, and habitat.
NOTE - (Scale for photos: 4 gridlines per inch)
Table of Contents:
*Phylum Porifera
*Phylum Cnidaria
*Phylum Bryozoa
*Phylum Brachiopoda
*Phylum Mollusca
*Phylum Arthropoda
*Phylum Echinodermata
*Phylum Protochordata
*References
Phylum Porifera
Porifera, more commonly called sponges, are composed of tiny needle like spicules that are made of lime, silica, or flexible sponging. They range in size from 1 to 200 cm. The majority of Porifera are found in marine environments, but there are some freshwater varieties. Most Porifera live attached to the sea floor. Porifera filter-feed by drawing water in through minute pores aided by whip like flagella on collar cells. Porifera reproduce both sexually and asexually. Porifera fossils first appeared in the Cambrian rocks and they are still present today.
Calcarea sponges are the only sponges that possess spicules composed of calcium carbonate.
Demospongia is the most diverse sponge group. Greater than 90 percent of the 5,000 known living sponge species are demosponges.
Phylum Cnidaria
Phylum Cnidaria includes the well-known jellyfish, sea anemones, and corals, in addition to hundreds of other classes of organisms. The majority of Cnidaria species in the fossil record are different types of coral. The two main types of coral are solitary and colonial. Both types are filter feeders with most species living attached to the sea floor in marine environments. They use specialized stinging cells to capture prey. Cnidaria reproduce both sexually and asexually. A distinguishing characteristic when looking at fossils from the Phylum Cnidaria is their radial symmetry around a vertical axis.
Colonial Coral, Order Tabulata
Colonial corals: More than one organism lived in these corals at one time. Each section housed a soft-bodied organism.
Solitary Coral, Order Rugosa: 
Solitary Corals: Only one soft-bodied organism lived in solitary corals. The life position of the specimen bellow (commonly called Horn Coral) consisted of the point touching the ground and the tentacles, of the soft-bodied organism, coming out of the opening where the septa are now visible.
Phylum Bryozoa
Bryozoans, otherwise known as Moss Animals, are commonly found in branching, encrusting, or fan forms. The majority of Bryozoans are marine, stationary, and colonial animals. They filter feed using a structure called a lophophore. Bryozoa reproduce both sexually and asexually. They occasionally resemble corals, but are more complex. They date from the Ordovician to the present.
Here are some commonly found shapes of Bryozoa:
Branching
Screw
Phylum Brachiopoda
Brachiopods, often called Lamp Shells, are extremely common marine invertebrate fossils. They attach themselves to the sea floor with a pedicle (fleshy anchoring stalk). They reproduce sexually and their swimming larval stage accounts for their broad geographic distribution. They feed using a structure called a lophophore to filter-feed. One major distinguishing characteristic of fossil brachiopods is the bilateral symmetry of their bivalve shells. There are two major classes of Brachiopods - Class Articulata and Class Inarticulata.
Line of symmetry in Brachiopods
Articulate Brachiopods:
Articulate Brachiopods are the most common type of Brachiopod. They have a definite hinge system and have relatively well developed teeth and sockets.
Articulate Brachiopod
Inarticulate Brachiopods:
Members of the Class Inarticulata have valves that are not hinged by teeth and sockets. The shells are often ornamented with weak concentric growth lines. Inarticulate Brachiopods use muscles to open and close the valves. In well-preserved specimens muscle scars are visible on the interior of the valves.
Name: Lingula sp. Locality: The Philippines/Estonia Age: Ordovician
Inarticulate Brachiopod
Mollusks have three classes whose animals are extremely common in fossil record. They live in both marine and freshwater environments. Some even live on land. Different species float, swim, burrow, and crawl. Some Giant Squids have reached a length of 60ft, and a few ancient clams weighed over 500 pounds. Still, other species of mollusks were microscopic.
Class Pelecypoda -
Pelecypods, otherwise referred to as bivalved mollusks are primarily marine invertebrates, though there are a few freshwater species. Clams, mussels, and oysters are living examples of mollusks. The two valves of the shell are usually identical; this separates them from the Brachiopoda. The two valves are joined along a hinge line and are held together by muscles and teeth. Pelecypods use a mechanism called a foot to take in food and oxygen from the water.
Class Gastropoda -
Gastropod fossils consist of one shell coiled around an axis in which a single soft-bodied organism lived. Snails, limpets, and abalones are examples of living Gastropods. They have eyes, tentacles, a mouth, and a broad muscular foot.
Class Cephalopoda-
Cephalopoda are highly developed marine mollusks. Living examples include squids and octopi. Unlike these well-known examples, most fossil Cephalopods had well-developed shells. They date back to the mid-Cambrian. Sutures and chambers in Mollusk fossils indicate the specimen is in the Class Cephalopoda.
Phylum Arthropoda
(Phylum of invertebrates that are bilaterally symmetrical with segmented bodies and paired jointed limbs)
Class Trilobita
Trilobites are a class of extinct marine arthropods that lived from the Cambrian to the Permian, that are related to the modern horseshoe crab. The class Trilobita is very diverse, and the different species are of great importance as Paleozoic guide fossils. Though were bottom dwelling predators and scavengers, some were probably capable of burrowing. Trilobites went through larval stages during their life. Often what appears to be a trilobite fossil at first is a molt of a trilobite.
A typical length is 3 cm.
Class Trilobita
The body has three major divisions and the thorax has three lobed segments. Many species have eyes.
Cambrian Asaphiscus wheeleri Meek
Wheeler Formation, Middle Cambrian, Antelope Springs, Utah, U.S.A.
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Phylum Echinodermata
Echinoderms are a phylum of marine animals. Present day Echinoderms include sea urchins and starfish. Most Echinoderms live on the sea floor or attached to rocks or other organisms. Echinoderms are covered with limy plates or spines.
Class Cystoidea - Cystoids are an extinct class of Echinoderms that existed from the Ordovician to the Devonian. They had rounded bodies made up of many irregular plates with triangular pore openings.
Class Blastoidea - Blastoids are an extinct class of Echinoderms that existed between the Ordovician and the Permian. Each cup has thirteen plates, symmetrically arranged with 5 petal shaped grooves.
Blastoid head
Class Crinoidea - Crinoids, more commonly known as sea lilies, are flower-like echinoderms. They vary in their shape, plates, and arms.
Crinoid fossil - including soft parts
Crinoid column
Class Echiniodea - Members of the class Echiniodea include sea urchins and sand dollars. Most species have spiny, flattened, globular, or heart shaped shells.
Echiniodea fossil
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Phylum Protochordata
Class Graptolithina
Graptolites are extinct marine colonial organisms that probably floated freely in the water. Most graptolites consisted of one or more chitinous branches called stipes that bare cup-like structures called thecae. Graptolite fossils look like pencil markings on gray or black shales. They are extremely important Paleozoic index fossils.
A stipe with visible thecae.
: 
Some scientists believe graptolites had a primitive central nervous system.
Levin, Harold L., 1999, Ancient Invertebrates and Their Living Relatives, Upper Saddle
River, New Jersey, Prentice Hall, p. 108-111, 126-128, 157-159, 176-180,203-207, 253-258, 294-300, 329-333.
Mayr, Helmut, 1985, A Guide to Fossils, Princeton, New Jersey, Princeton University
Press, p. 1-31.
Moore, R.C., Cecil L.G., and Fischer A.G., 1952, Invertebrate Fossils, New York,
McGraw-Hill Book Company, Inc., p. 156-162, 197-207, 268-272, 276-280.
Rhodes, F.H.T., Zim, H.S., Shaffer, P.R., 1962, Fossils: A Guide to Prehistoric Life,
Racine, Wisconsin, Western Publishing Company, Inc., p.75-131.
Stearn, C.W., and Carroll, R.L., 1989, Paleontology: The Record of Life: New York, John
Wiley & Sons.
Zuckerman, Sarah, and Hinterthuer, Adam. Poster: Fossil Guide for Beginners, May, 2001.
Photographs found at the following web sites:
http://www.toyen.uio.no/palmus/galleri/montre/english/a31325.htm
No Author, University of Oslo, Norway, 2001
http://canes.gsw.edu/~daskren/fossil.htm
Dan Askren, Dept. Geology & Physics, Georgia Southwestern State University, Americus GA July 22, 1997