Who invented the dichotomous key

Bio Lab Classification And Evolution

Overview
Taxonomy is the study of the classification of organisms. Classification is simply a way of sorting things in an orderly manner. For example, if you have a box of mixed stationary supplies on your desk—paper clips, staples, rubber bands, and thumb tacks—and you decide to put them into four separate containers so that you can use them more efficiently, you are classifying them.

There are at least two million species of organisms alive on the planet right now, most of them insects. There have been many other species that are now extinct. To try to keep them in some kind of order to examine, compare, and discuss them in a consistent manner, biologists have set up a system known as the binomial system of nomenclature. In this system, two names are assigned to each organism, a genus name and a species name. The genus name indicates the group of related species to which the organism belongs, and the species name indicates the specific species.

For example, the scientific name for a chimpanzee is Pan troglodytes. Pan is the genus name, and troglodytes is the species name. By convention, both words are written in italics or underlined. Note that the more general term comes first. If the American president Abraham Lincoln had been a species all by himself, his name would have been Lincoln abraham.

Starr (2000, glossary) defines a species as "one kind of organism." Among sexually reproducing organisms, a species is a group of naturally interbreeding organisms that form a genetically distinctive population reproductively isolated from all others. Your textbook provides greater detail on the technical definition of a species.

A group of closely related species forms a genus. The plural of genus is genera. Genera are grouped into families, families into orders, orders into classes, classes into phyla (the single is phylum), and phyla into kingdoms. These levels are grouped based on their common characteristics. Your textbook discusses some of these defining characteristics in some detail.

The value of this system is that it not only gives each species a name, but that it also puts it in a series of categories that indicate its relationship to other similar species and also to more distantly related ones.

Let's go back to the chimpanzee. Pan troglodytes belongs to the family Pongidae, which includes the gorillas and the orangutans. They all have distinctive molar teeth; flexible arm and shoulder joints; arms longer than legs; and large complex brains. None of them have a tail. The Pongidae belong to the order Primata, which includes, in addition to the Pongidae, all the monkeys and the prosimians, such as lemurs. All of these animals are grouped together because they share a large group of behavioral and anatomical characteristics. These include excellent manual dexterity, a well-developed sense of sight, a dependence upon learned behavior, a long infant-dependency period, a complex social organization, prehensile hands with opposable thumbs, mobile arms, binocular vision, and a reduced snout.

The primates belong to the class Mammalia, which are animals with hair or fur, high and controlled body temperature, glands that produce milk, and complex teeth. The mammals belong to the phylum Chordata, all of which have, at some stage in their development, a dorsal stiffening rod (notochord) as the chief internal support, a tubular nerve cord above the notochord, gill slits leading into the anterior part of the digestive tract, and a post-anal tail. In a chimpanzee, most of these disappear during embryonic development, but they are all there at some stage.

Finally, the chordates belong to the kingdom Animalia. All animals are multicellular heterotrophs that usually ingest food and digest it in an internal cavity. Their cells lack the rigid cell walls that characterize plant cells. Most animals are capable of complex and relatively rapid movement and most reproduce sexually.

As you can see, a taxonomic system goes from very specific characteristics to very general ones. This information can be used to create a dichotomous classification key, which is very simply a system for identifying organisms in the field. At each step, you are given two choices for a given characteristic; these lead you to further choices more specifically identifying the species until you finally have its name (or if you're really lucky, a discovery of a new species).

Lab Activities
A. Using a Dichotomous Key
Lab Materials
Materials in your lab kit:

· none needed

Being able to use a dichotomous key is a very useful skill. Many field guides, particularly ones that help you to identify plants, are based on this principle. In this activity, you will use a classification key to determine the names of nine species of fish. To do so, you begin with the first pair of choices on the key, working your way downward until you've successfully identified the fish.

1. Review the following definitions and key to get a feel for what you will be looking for in identifying the fish.

Definitions

dorsaltoward the backbone side of the fish

ventraltoward the belly side of the fish

caudaltoward the tail end of the fish

pharynxthe throat region of the fish behind the head

pectoral finthe fin on the side of the fish nearer the head

pelvic finthe fin on the side of the fish nearer the tail

Simple Classification Key for Some Pacific Fishes

Choice

Characteristic

Next Move or Identification

1a

Fish has 5 or 6 gill openings on each side of the pharynx

2

1b

Fish has only one covered gill opening on each side of its pharynx

3

2a

Very large, stout bodied; caudal fin is crescent shaped and nearly symmetrical

White shark

2b

Large, slender bodied; dorsal lobe of caudal fin is much longer than the ventral lobe

Blue shark

3a

One eye on each side of the head

4

3b

Both eyes on one side of the head

Flathead sole

4a

Pectoral fins and pelvic fins present

5

4b

Pectoral and pelvic fins absent

Moray eel

5a

One dorsal fin

6

5b

More than one dorsal fin

7

6a

Long winglike pectoral fin

California flying fish

6b

Small pectoral fin low on side

8

7a

2 dorsal fins

Great sculpin

7b

3 dorsal fins

Pacific cod

8a

Large black oval spots over all of upper body and caudal fin

Pink salmon

8b

Fine specks on back, but no black spots

Chum salmon

2. Using the key above, identify the following fish and type the name of each fish next to its letter: (type your answers in the BOXES below each fish):

image1.png

image2.png

image3.png

A image4.wmf

B image5.wmf

C image6.wmf

image7.png

image8.png

image9.png

D image10.wmf

E image11.wmf

F image12.wmf

image13.png

image14.png

image15.png

G image16.wmf

H image17.wmf

I image18.wmf

(Fish drawings copyright by Houghton Mifflin and Eschmeyer & Herald)

References
Eschmeyer, W. N., and E. S. Herald. (1983). The Peterson field guide series: A field guide to Pacific coast fishes—North America. New York: Houghton Mifflin. (Plates 2, 6, 8, 11, 12, 16, 45)

Gendron, Robert P., Ph.D. (2000). "Classification and evolution." Indiana University of Pennsylvania Biology Department. Retrieved April 18, 2002, from http://nsm1.nsm.iup.edu/rgendron/camin.htmlx .

Starr, Cecie. (2000). Basic concepts in biology. 4th ed. Stamford: Thompson.

B. Taxonomic Classification
Materials in your lab kit:

· none

Additional materials you will need:

· scissors (optional)

(The following exercise was modified from one designed by Robert P. Gendron, Ph.D., of Indiana University of Pennsylvania. His permission to use it is gratefully acknowledged.)

In order to design a dichotomous key for a group of related organisms, you must first examine your specimens and determine their specific characteristics. Then you must use these characteristics to categorize them into larger and larger groups such as genera, families, orders, and classes. In the overview for this lab, you were given the description of the classification of the chimpanzee as an example. For this exercise, you are going to design a dichotomous key to sort fourteen living species of caminalcules, which are imaginary animals invented by the evolutionary biologist, Joseph Camin. These animals are pictured below:

Living Caminalcules

image19.png

(Caminalcule pictures copyright by Systematic Biology and Robert R. Sokal.)

image20.png

Supersize me version (

Print this out and cut out each one to help you rearrange and re-examine them.

Each caminalcule has a number designation as its common name. You may consider these drawings to be life size. Examine the pictures and note the variety of appendages, shell shape, color pattern, size, and any other details that you notice. You may find it easier to do this if you print the page, cut out the creatures, and move them around on your physical desktop.

Now create a hierarchical classification of these species, using the format in the table below. Instead of using letters (A, B, etc.), as in this example, use the number of each caminalcule species. Keep in mind that the classification scheme below is just a hypothetical example. Your classification may look quite different from this one.

Sample Classification Scheme

Phylum Caminalcula

Class 1

Class 2

Order 1

Order 2

Order 3

Family 1

Family 2

Family 3

Family 3

Genus 1

Genus 2

Genus 3

Genus 4

Genus 5

Genus 6

A

G

H

D

B

J

L

E

K

C

F

I

1. The first step in this exercise is to decide which species belong in the same genus. Species within the same genus share characteristics not found in any other genera. The caminalcules numbered 19 and 20 are a good example; they are clearly more similar to each other than either is to any of the other living species here, so we would put them together in their own genus. Use the same procedure to combine the genera into families. Again, the different genera within a family should be more similar to each other than they are to genera in other families. Families can then be combined into orders, orders into classes and so on. Depending on how you organize the species, you may only get up to the level of order or class. You do not necessarily have to get up to the level of kingdom or phylum.

One of your problems will be convergent evolution; this is a real problem faced by taxonomists every day. Look up convergent evolution in your textbook or some other reference to learn the meaning of the term.

2. Define this term in your own words and explain why it may cause you problems in this exercise. (Here is a hint: claws have arisen independently in caminalcules more than once during evolution.)

Type in here – this expands as you type.

Definition: Convergent evolution + why it may cause problems in taxonomy

3. Enter your classification scheme here. It does not have to be as elegant as the sample scheme above, but it does have to be clear. If you are uncertain how best to input your classification scheme, contact your instructor.

Type in here – this expands as you type.

image21.png

Classification Scheme:

4. Use your classification scheme to design a dichotomous key that will account for the fourteen species. Remember that in each step you can only have two choices. One problem you may have is that your steps will have numbers and so do your species. To keep things clear, refer to the names of the species by using the number with the # symbol in front of it. In other words, the fourteen species names will be #1, #2, #3, #4, #9, #12, #13, #14, #16, #19, #20, #22, #24, and #26.

a. Enter your dichotomous key here. If you are uncertain how best to input your dichotomous key, contact your instructor. Note: Table headings are as follows (see pp 3-4):

Choice

Characteristic

Next Move or Identification

Type in here – this expands as you type.

image22.png

References
Eschmeyer, W. N., and E. S. Herald. (1983). The Peterson field guide series: A field guide to Pacific coast fishes—North America. New York: Houghton Mifflin. (Plates 2, 6, 8, 11, 12, 16, 45)

Gendron, Robert P., Ph.D. (2000). "Classification and evolution." Indiana University of Pennsylvania Biology Department. Retrieved April 18, 2002, from http://nsm1.nsm.iup.edu/rgendron/camin.htmlx .

Starr, Cecie. (2000). Basic concepts in biology. 4th ed. Stamford: Thompson.

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