General Biology Activity

Who’s On Next?


·         Set of fossil cards

·         Set of sketches of fossil marine organisms

Prelab Question

What is relative dating? (And no, I am NOT talking about you cousin!)





1.      Examine the cards and set of sketches. Each card in you set represents a particular rock layer showing fossils located in that layer. All of the fossils represent marine organisms deposited in sedimentary rock. The set of sketches of marine organisms provides background information on the individual fossils.

  1. The card representing the oldest rock layer is marked with the letter “M” in the lower left corner. The letters on the other cards have no significance to their sequencing procedure. Ignore the other letters for now.
  2. Place the card with the letter “M” on the lab table (face up).
  3. Find another card (rock layer) that has at least one of the fossils you found in the oldest rock layer. This rock layer would be younger than the first because there are new fossils in the layer.
  4. Continue to place cards in this manner to arrange the card from oldest to youngest with the oldest layer on the bottom and the youngest layer on the top.
  5. Remember: Extinction is forever! Once an organism disappears from the sequence it cannot reappear later.
  6. Sequence your cards in a vertical stack of fossils and rock strata.
  7. Identify the layers from youngest to oldest by writing the letters in the blanks.











1.      What is an “index fossil?” Which of the animals in this activity are classified as index fossils?





2.      What kind of environment did ammonites live in? What modern-day animals are relatives of ammonites?



3.      When did horn corals evolve?



4.      How many species of brachiopods are living today?



5.      To what phylum of animals do trilobites belong? How long were the largest trilobites?




6.      Until the 17th century, what did scholars think fossilized shark teeth were? Why are teeth often the only part of a shark that is fossilized?






7.      List the habitats that include gastropods. (Point out the one that surely HAS to be a typo – no snail would live in one of these!)




8.      What does the word “ichthyosaur” mean? Were ichthyosaurs a type of fish? Explain.




9.      What do scientists think the heavy armor on a placoderm’s head could have been used for? Do placoderms have any modern-day descendents?




10.  What are eurypterids often referred to as? Where did eurypterids live?





11.  What are crinoids sometimes called? Who are their close living relatives?





12.  What is the difference between a pelecypod and a brachiopod? What is the common name for pelecypods?





13.  How long have benthic foraminifera existed on earth? Why have they managed to live for so long when so many other species have become extinct?






14.  When did graptolites live? What do scientists think they ate?


What are Trilobites?

Trilobites are hard-shelled, segmented creatures that existed over 300 million years ago in the Earth's ancient seas. They went extinct before dinosaurs even came into existence, and are one of the key signature creatures of the Paleozoic Era, the first era to exhibit a proliferation of the complex life-forms that established the foundation of life as it is today. Although dinosaurs are the most well-known fossil life forms, trilobites are also a favorite among those familiar with Paleontology (the study of the development of life on Earth).

Trilobites were among the first of the arthropods, a phylum of hard-shelled creatures with multiple body segments and jointed legs (although the legs, antennae and other finer structures of trilobites only rarely are preserved). They constitute an extinct class of arthropods, the Trilobita, made up of nine orders, over 150 families, about 5000 genera, and over 15,000 described species. New species of trilobites are unearthed and described every year. This makes trilobites the single most diverse group of extinct organisms, and within the generalized body plan of trilobites there was a great deal of diversity of size and form. The smallest known trilobite species is just under a millimeter long, while the largest include species from 30 to 70 cm in length (roughly a foot to two feet long!). With such a diversity of species and sizes, speculations on the ecological role of trilobites includes planktonic, swimming, and crawling forms, and we can presume they filled a varied set of trophic (feeding) niches, although perhaps mostly as detritivores, predators, or scavengers. Most trilobites are about an inch long, and part of their appeal is that you can hold and examine an entire fossil animal and turn it about in your hand. Try that with your average dinosaur!

cephalon, thorax, and pygidium

all line drawings ©1999, 2000 by S. M. Gon III

Whatever their size, all trilobite fossils have a similar body plan, being made up of three main body parts: a cephalon (head), a segmented thorax, and a pygidium (tail piece) as shown at left. However, the name "trilobite," which means "three lobed," is not in reference to those three body parts mentioned above, but to the fact that all trilobites bear a long central, or axial lobe, flanked on each side by right and left pleural lobes. These three lobes that run from the cephalon to the pygidium are what give trilobites their name, and are common to all trilobites despite their great diversity of form.

Information obtained from the following website:

three lobes: left, right, and middle (axial)


What is a Gastropod?
(gas-tro-pod-a:  Latin meaning:  gaster=stomach  pous=foot :  stomach - foot!)

    Cypraecassis rufa
 (by permission of Guido Poppe)
     The gastropoda is the largest and most certainly the best-known class of all the molluscs.  They are the most successful of the molluscan classes, and occupy almost every habitat on earth, from desserts to high mountains, fields, forests, lakes, streams and oceans - and most probably your back yard!!  It is the only class to contain species that have ventured permanently on to land.  (To do this, snails evolved an efficient gliding foot, eyes, an aggressive eating mechanism and a pulmonary system for breathing.) 

Gastropods also inhabit every niche in the ocean from the intertidal zone to the deepest ocean trenches. Over 15,000 fossil forms have been described and over 40,000 species exist today.  They are, scientists theorize, now at the peak of their evolutionary development.



What is a Crinoid?


Crinoids, sometimes called ''sea lilies'', are marine animals characterized by an exoskeleton of calcite plates, jointed arms that radiate from the body, and usually by a stem that attaches the animal to a substrate - usually the sea floor. Crinoids are echinoderms and are closely related to sea urchins and starfish. These ''spiny skinned'' organisms first appeared during Early Ordovician times and are still living today. During the Paleozoic Era, they became very abundant. In fact, the Mississippian Period has long been known as the "Age of Crinoids". Vast colonies of crinoids lived in shallow seas during this time, and their remains built up beds of limestone hundreds of feet thick.

Information obtained from the following website:


What is a Pelecypod?

Pelecypods (clams) are bivalved mollusks and are common in the oceans and streams of the world today. Pelecypod fossils are common in some places in Kentucky, but they are often confused with the more abundant brachiopods. Although both brachiopods and pelecypods have two valves (shells), they are quite different. Typically the two shells of a pelecypod are alike except that they are mirror images of each other. The two shells of the brachiopod are not alike. The animal living inside the brachiopod shell is very much different compared to the one living in the pelecypod shell. Brachiopods are rare today.

Information obtained from the following website:


What is an Ichthyosaur?

While dinosaurs ruled the land, the ichthyosaurs shared the seas of the world with the other great groups of large marine reptiles, the plesiosaurs and mosasaurs. "Ichthyosaur" means "fish lizard” – an apt name. The earliest ichthyosaurs had long, flexible bodies and probably swam by undulating, like living eels. More advanced ichthyosaurs—like the one shown above, on display at the Senckenberg Museum in Frankfurt, Germany—had compact, very fishlike bodies with crescent-shaped tails. The shape of these ichthyosaurs is like that of living tunas and mackerels, which are the fastest fish in the ocean; like them, the later ichthyosaurs were built for speed. Note the paddles with which ichthyosaurs swam; they have the same basic plan as your hand and arm, but the arm bones are very short, while the fingers have lengthened by developing many more bones than the three that make up each of your fingers.

Rare fossils have been found that show ichthyosaurs actually giving birth to live, well-developed young; ichthyosaurs never had to leave the water to lay eggs. In fact, from their streamlined, fishlike bodies, it seems almost certain that ichthyosaurs could not leave the water. Yet they still breathed air and lacked gills, like modern whales.

Ichthyosaurs were not dinosaurs, but represent a separate group of marine vertebrates. Because ichthyosaurs were so specialized and modified for life in the ocean, we don't really know which group of vertebrates were their closest relatives. They might have been an offshoot of the diapsids—the great vertebrate group that includes the dinosaurs and birds, the pterosaurs, the lizards and snakes, and many other vertebrates. On the other hand, some have suggested that the ichthyosaurs were descended from a distant relative of the turtles.

The first ichthyosaurs appeared in the Triassic. In the Jurassic, ichthyosaurs reached their highest diversity, and then began to decline. The last ichthyosaurs disappeared in the Cretaceous—several million years before the last dinosaurs died out. Whatever caused the extinction of the dinosaurs did not cause the ichthyosaurs to die out.

Information obtained from the following website:


What is a Eurypterid?

Sea Scorpion - Eurypterid four hundred million years ago during the upper Silurian period. ,

Member of an extinct order (Eurypterida) of arthropods, similar in body plan to the horseshoe crab, that lived c. 505–245 million years ago.

Frequently referred to as giant scorpions, most eurypterids were small, although Pterygotus buffaloenis, a species from the Silurian period, was the largest arthropod ever known, reaching a length of about 10 ft (3 m). The eurypterids lived in brackish waters. Some were predators; others were probably bottom-dwelling scavengers.

Information obtained from the following website:





What is a Placoderm?

The placoderms are among the most ancient of fish, and, along with the Acanthodii, the only class of (gnathostomes) to become completely extinct.  The name "placoderm" is from the Greek and means "tablet + skin", referring to the heavy armored bony plates that completely covered the head and thorax of these curious prehistoric fish.

   They are easily distinguished from the earlier jawless fish by their paired fins and presence of jaws, an adaptation that gave them a tremendous advantage, for it enabled them to bite solid food rather than simply suck up organic particles from the mud.  Yet still these creatures were very primitive compared to other fish.  Placoderms lacked teeth, but biting or grinding structures are often found in the dermal bones lining their mouths. 

Although the head and thorax were heavily armored with dermal (skin) bone, the rest of their bodies were quite vulnerable, covered with small bony scales or lacking even that.  It is not clear what purpose this armor may have served.  It has been suggested that it was a defense against the giant sea-scorpions that inhabited brackish water environments around this time. 

Placoderms evolved into a variety of body types, including torpedo-shaped swimmers, flattened bottom-dwellers, and armored box-like types.  They included both carnivorous and detritivorous types.  The paired fins and a heterocercal tail indicates they could swim quite efficiently when they wanted to, but the heavy armor would've weighed them down, and it is likely they spent much of their time sitting on the bottom.

Although they first appeared during the early Silurian period, the placoderms did not become common or widespread until the Early Devonian.  They soon came to dominate most brackish and near-shore ecosystems, and also spread to marine and freshwater environments.  More than 250 genera are known in all. They all suddenly died out at the Devonian/Carboniferous boundary, without leaving any descendents.

Information obtained from the following website:


What is a Horn Coral?
Horn coral is a type of large, horn-shaped coral (order Rugosa) that lived as a solitary individual or as a colony. This invertebrate evolved during the Ordovician Period, roughly 500 million years ago. Horn corals are important index fossils. Their fossils are also sometimes used to determine the length of the day (and the year) in the distant past due to the manner in which they grew.

What are Foraminifera ?

Foraminifera are unicellular protists that construct shells of one to many chambers. They either live in and on the sediments of the sea floor (benthos) or freely float amongst the marine plankton (planktic). Foraminifera are among the most abundant, diverse and widely distributed protists in the ocean and play a significant role in the economy and balance of the biosphere. They inhabit virtually all marine environments, ranging from the poles to the equator and from the shallow intertidal to the deep ocean. To date, approximately 60000 fossil and Recent species and 3620 genera have been validly recognized. Their skeletal remains often make up considerable amounts of sedimentary rock.

The fossil record of benthic foraminifera is ancient, dating to more than 550 million years. Planktic species range to approximately 190 million years.

There is hardly any oceanic habitat that has not been colonized by foraminifera. They inhabit deep-sea as well as shallow intertidal environments and also have been reported from extreme habitats such as Arctic sea ice, low-oxygenated lakes, and from around deep-sea hydrothermal vents. Their ecological flexibility to colonize even the most remote and extreme territories of the ocean is probably the major reason why foraminifera have successfully survived major extinction periods during the earth’s history.

Information obtained from the following website: http://www.paleontology.uni-bonn


What are Ammonites?

Although relatively simple in form, ammonites are extremely rich in the information they yield to scientists. These extinct marine animals, which thrived in the Paleozoic and Mesozoic Eras, some 400 to 65 million years ago, were cephalopods, and are thus related to squid, octopus, cuttlefish, and the chambered nautilus.

Ammonites were able to swim, thanks to the unique construction of their shell, which was divided into a series of air chambers. The air in the chambers provided buoyancy for the animal to float; like modern cephalopods, they probably moved through the water using jet propulsion.

Fossils of ammonites are found all over the world. As different species of ammonites lived during different time periods, scientists can use these animals to determine the relative age of the rocks in which their fossils are found (such fossils are called "index fossils"). Because ammonites lived exclusively in marine environments, their presence also indicates the location of prehistoric seas.

Many ammonites, including this example, preserve their original shell material and are quite beautiful. Scientists at the American Museum of Natural History are currently studying the evolution and life history of these ancient creatures.

Information obtained from the following website:

What is a Brachiopod?

Brachiopods are marine animals that, upon first glance, look like clams. They are actually quite different from clams in their anatomy, and they are not closely related to the molluscs. They are lophophorates, and so are related to the Bryozoa and Phoronida.

Although they seem rare in today's seas, they are actually fairly common. However, they often make their homes in very cold water, either in polar regions or at great depths in the ocean, and thus are not often encountered. There are about 300 living species of brachiopods.

Despite their relative obscurity today, brachiopods have a long and rich paleontological history. During the Paleozoic era, they were extremely abundant. They diversified into a number of different morphologies and even participated in the build-up of ancient reefs. At the end of the Paleozoic, some 250 million years ago, they were decimated in the worst mass extinction of all time, the Permo-Triassic event. Their numbers have never been as great since that time.

Information obtained from the following website:


What is a Graptolite?

The graptolites in the picture are Cyrtograptus sakmaricus (the spiral, branching specimen) and Pristiograptus nudus (the straight one.) The straight specimen is 4 cm long.

Graptolites are a group of extinct, marine invertebrates, that thrived in the Early and Middle Paleozoic seas. Most were planktonic, living within oceanic waters and probably feeding on bacteria and other microscopic marine life. Each specimen represents a colony of many individual animals, each approximately 1-2 mm in size and interconnected by common tissue throughout the colony. Their closest living relatives are probably a group of animals known as pterobranchs, belonging to the phylum Hemichordata. Graptolites are the most important group of fossils for determining ages of sedimentary rocks of the Ordovician, Silurian and Early Devonian periods (ca. 500-400 million years old). In fact, graptolite occurrences are the basis on which these intervals of geologic time are defined. As a result, they have gained considerable importance in studies of sedimentary basin history and global correlation of important geological events. They are also sensitive indicators of changing climate and oceanic conditions through the interval in which they lived.

Information obtained from the following website:



   What Are Sharks?

Fossil shark teeth embedded in a piece of Miocene limestone from Victoria in Australia. Detailed examination of such remains has enabled scientists to piece together the complex story of how life evolved on earth.

The early evolutionary history of sharks and shark-like fishes is still poorly understood. Until recently scientists thought that there were no shark fossils to speak of in rocks older than those from the Middle Devonian. Now, however, it is certain that sharks did not appear suddenly at that time -it was just that researchers were looking for the wrong kind of evidence. Microscopic examination of ancient sediments has revealed fossilized remains of sharks which may push their origins back at least 50 million years further.

All that is known about ancient sharks and their evolution has been gleaned from the fossil record. Fossil remains of sharks have been known for many centuries, although their true nature was not always recognized. Until the 17th century many scholars regarded such fossils as sports of nature, and thought that fossilized shark's teeth were bird's or snake's tongues. Some large fossil teeth, called glossopteris (literally tongue-stones), were used as amulets to ward off evil and to protect against poisoning. It was not until about 150 years ago that the study of fossils, paleontology; became a science, and the ancient remains of plants and animals were systematically classified.  

Sharks are rarely found as complete fossils because their skeletons are made of cartilage. Normally only the hard parts, such as teeth, scales and fin spines, are found. However, under certain special conditions, complete fossil sharks are preserved, and these provide scientists with vital information.

Information obtained from the following website: