Name: _____________________________________ Date: _____________

Period: _____ Living Environment

Introduction

A dichotomous key is a reference tool used mainly in biology. It allows the user

to determine what an organism is by answering numerous questions that have

only two possible answers. Ultimately, the answers will point to a specific

organism or some higher taxonomic level. Dichotomous keys can be very broad

or extremely specific. To create a key, you need a working knowledge of the

differences between groups of organisms. The more specific the key, the more knowledge you need.

A Phylogenetic tree is a diagram that shows connections between organisms and shows their relative

ancestry towards one another. Phylogenetic trees are very useful in evolution because they can show progression

of change within a group of organisms.

How to create a dichotomous key.

1. Determine the level of specificity your key will need. For instance, your key can simply identify different

type of animals or it can try to determine exactly what type of bacteria a user is observing.

2. Develop questions that will differentiate between organisms. Broad questions can be along the lines of

"Is it a fish or a reptile?" More specific questions would be along the lines of "Has a small black spot on its

tail?" Each question should have only two possible responses.

3. Keep developing questions that will differentiate between more and more similar organisms until you

reach the level of specificity you desire.

4. Write the first question on your key at the top of the page in the center, and draw two lines branching out

from beneath it. Each line will point to one possible answer. Write the answers at the end of each line.

5. Continue branching your questions in the same fashion. If at any time you can positively identify a

species or group, write the species or group name below the answer to the last question. Example

dichotomous keys can be found by following the reference links.

Classification of Organisms

Creating a Dichotomous Key

Lab

#28

Procedure

1. Study the 12 dinosaurs in the diagram. Look for similarities among them and differences that may

make them unique.

2. Create a Phylogenetic Tree by filling in the missing squares with the right descriptions.

3. Once the Phylogenetic Tree is completed, use it to create a dichotomous key using the directions

in the direction bank below it

4. REMEMBER- Look for similarities than at differences. The first instructions should separate

the dinosaurs into 2 groups After the 2 groups are made, use another instruct to further divide the

group into smaller groups until you get to a single individual.

Word bank

1 Bump

2Bumps

Armor Down Back

Hooked Claw

Horns

Long Neck

No Hook Claw

No Horns

Plates Down Back

Sail Down Back

Short Neck

Spikes Down

Back

Spikes on Side

1a. Has 2 legs

1b. Has 4 legs

2a.

2b. Allosaurus

3a.

3b.

4a. Corythosaurus

4b. Lambeosaurus

5a. Velociraptor

5b. Ornithomimus

6a. Brachiosaurus

6b.

7a.

7b.

8a. Protoceratops

8b. Triceratops

9a. Ankylosaurus

9b.

10a. Dimetrodon

10.b

11a. Stegosaurus

11b. Kentrosaurus

Direction Bank Use these directions to fill in the dichotomous key above

Has armor down back Has a long neck

Has boney spikes down its back Has a long neck

Has boney plates down its back Has no crests on head

Crest has one bump Has no horns on head

Crest has two bumps Has a sail on its back

Has a crest on the head Has a short neck

Has a frill (boney plate that protects the neck) Has a short neck

Has horns on head Has small claws on its feet

Has horns down the side of back Has projection down the center of back

Has a hook claw on its toe Has protection down it back

Allosaurus

Lambeosaurus Triceratops

Ornithomimus Corythosaurus Ankylosaurus

Kentrosaurus

Brachiosaurus Stegosaurus

Protoceratops

Dimetrodon Velociraptor