1. Identifying Organisms – Dichotomous Keys
Bio3.5.2 Analyze the classification of organisms according to their evolutionary relationships (including: dichotomous keys and phylogenetic trees)

2. DICHOTOMOUS KEY
A dichotomous key - a special tool used to identify organisms and objects.
arranged in steps with two descriptive statements at each step
- at the end of the statement is either the name of the organism or directions to go to a next step.

3. DICHOTOMOUS KEY
They may be laid out in various ways, but usually form a series of numbered questions arranged in “couplets” as shown below: 1. Bark on trunk smooth Bark on trunk rough Bark mostly white Bark other colors

4. DICHOTOMOUS KEY
Sometimes they are laid out differently:

5. Rules to Follow When Using a Dichotomous Key
Always read both choices, even if the first seems to be the logical.
For example:
1. Bark on trunk smooth
Bark on trunk rough
2. Bark mostly white
Bark other colors
Read first!!

6. Rules to Follow When Using a Dichotomous Key
2. Understand the meaning of the terms involved in the key. 3. When measurements are given, use a scale to measure the specimen. Do not guess at a measurement.

7. DICHOTOMOUS KEY EXAMPLE
Think of a dichotomous key as a type of scavenger hunt.
Example of dichotomous key
Example of dichotomous key
Interactive dichotomous key

8. Now it’s your turn!!! Lets try to classify some “Wacky People”
Lets look at ONE wacky person…You always do one organism at a time! Follow the key and answer the questions based on his characteristics.

9. Now it’s your turn!!! Two feet ……………………………………... 2
Always look at 1 first, then
follow where you should go
Two feet ……………………………………... 2
Some other number of feet …………….... 3
2 Does not look at all human ………………….4
Looks like a human …………………………..5
One leg ………………………………………..6
Three or four legs ……………………………7
So where do we go?
More than 2 feet, go to 3 (skip #2)
So where do we go?
Three or four legs go to 7 (skip 4, 5 and 6) Always go where it tells you too!

10. 4 Fly – like (does it look like a fly) …………... Mosk Cara
Rember to skip 4, 5 and 6
Go trait to 7!
4 Fly – like (does it look like a fly) …………... Mosk Cara
Not fly – like ……………………………….... 3
5 Seems like a girl…………...………………….Rita Nita
Not a girl …………..…………………………..5
6 Leg is curled, two feet………………………..Ru-ela Brella
Three or four legs …………………………..Giggles
Three legs …………………………………….10
Four legs ……………………………………...11
four legs go to 11 (skip 7, 8, 9, 10) Always go where it tells you too!
So where do we go?

11. 8 Has webbed feet…………….…………...Hex Oculate
Rember to skip 7, 8, 9 and 10
Go trait to 11!
8 Has webbed feet…………….…………...Hex Oculate
Clawed feet……………………………
9 Curly hair, no toes …...………………….Lugio Wirum
Wiggly looking mouth, 3 toes on feet .... C. Nile
10 Very long nose, open mouth.……….. Elle E. Funk
Some other appearance ……………..13
11 Has duck bill, two pinchers ………….Tri D. Duckt
No arms or pinchers ………………...14
No arms or pinchers go to 14 (skip 12, and 13) Always go where it tells you too!
So where do we go?

12. Patterned mulywumpus!!! 12 Has ears, tail and beak .….…………...Grif Leon
Rember to skip 12 and 13
Go trait to 14!
12 Has ears, tail and beak .….…………...Grif Leon
Four eyes on stalks………………….... Eggur Ondy
13 One eye, webbed feet………………….Cue Kide
Four stalked eyes, four pinchers… Quadrumenox
14 Three toes feet, nose like a flower….. Tunia petalos
Spider-like, has spots ….……………..Patterned mulywumpus
So what is our Wacky persons name?
Patterned mulywumpus!!!

13. You did it! Would you like to classify some more wacky people?
Let’s do two more together and then you can work on the rest by yourself! Remember, just follow the directions in the key and always go where it tells you to!
Here’s our new wacky person!

14. Two feet ……………………………………... 2 Some other number of feet …………….... 3
Always look at 1 first, then
follow where you should go
Two feet ……………………………………... 2
Some other number of feet …………….... 3
2 Does not look at all human ………………….4
Looks like a human …………………………..5
3 One leg ………………………………………..6
Three or four legs ……………………………7
So where do we go?
2 feet, go to 2!
So where do we go?
Not human, go to 4! (skip #3)

15. Mosk Cara!! 4 Fly – like (does it look like a fly) …………... Mosk Cara
Rember to skip 3 and
Go trait to 4!
4 Fly – like (does it look like a fly) …………... Mosk Cara
Not fly – like ……………………………….... 3
So what is our Wacky persons name?
Mosk Cara!!
And you are done! You don’t need to look at the rest of the key! How fun is this!!!???

16. Now you need to name the rest of the Wacky People
Now you need to name the rest of the Wacky People! Have fun and Good luck!!!