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.
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.