- slide 1 of 2
Divide and Classify with a Dichotomous Key
A dichotomous key is a guide to help users identify an organism. Scientists use dichotomous keys to classify organisms so they can be studied and organized by characteristics. For example, if you were looking at a panda bear and a raccoon, you may think they belong to the same family, but by further study, you will find they are not the same family of animals. By asking a series of question couplets (pairs) which divide the groups by similarities, a dichotomous key will eventually lead a user to correct identification of the organism.
Mammals are warm-blooded animals, covered in hair or fur, with a backbone, which nurse their young. A dichotomous key can help identify the family group and specific identity of mammals by asking a series of questions. A key can only help identify the specific group of mammals for which it was developed. For example, a key developed to identify marine mammals would not correctly identify a land mammal.
The word dichotomous comes from two Greek words that mean divide in two parts. To make a dichotomous key you will choose characteristics which can be used to divide a collection into two parts. You will continue to divide the groups in two until all the groups have only one member. Dichotomous keys can be developed to identify anything.
- slide 2 of 2
Step one: Gather pictures and information about the collection of mammals for which you wish to develop a key. For the example: raccoon, opossum, bat, skunk, and kangaroo.
Step two: Decide which characteristic will be used to divide the group in two. Record the characteristic and the groups formed. The first division will be labeled as #1 and the two questions as 1A and 1B. You will need to develop two papers; one with only questions and another with the questions and the formed groups to use as an answer key.
A. The animal has a pouch for carrying its young. Go to Step 2. (Kangaroo, opossum)
B. The animal does not have a pouch. Go to Step 3. (Raccoon, skunk, bat)
Step three: After the collection has been divided into two groups, divide the first group (A) into two more groups based on one characteristic. When a group with only one animal is formed, name it.
A. The animal walks/hops on its hind legs. The animal is a kangaroo.
B. The animal walks on all four legs. The animal is an opossum.
Step four: When all the mammals from group A have been identified, repeat the process with group B.
A. The mammal flies. The animal is a bat.
B. The mammal does not fly. Go to question 4. (Skunk, raccoon)
Continue to identify characteristics and divide groups until all of the mammals are named. Have a friend try out your key to see that it leads users to correct choices.
- Photo credit: Wikimedia Commons/Igno2
- Collin College. Dichotomous Key to Animals of Southwest Ohio.