Constructing a Chordate Cladogram
Images obtained from Phylopic, Creative Commons License
What is a cladogram?
A cladogram is a diagram that shows relations among organisms. A cladogram uses lines that branch to end at groups of organisms with a common ancestor. The image shows the relationship among groups A, B, and C. Closely related organisms will have one or more SHARED TRAITS, indicated by the green and orange circles.
1. Which two organisms are most closely related?
2. The green dot indicates a trait that is shared by every animal on the diagram. Suggest a trait that would apply.
3. Animals A & B share a trait that animal C does not have, indicated by the orange circle. Suggest a trait that would apply.
An example of a cladogram of heloderms (Gila Monsters):
Individual subspecies within the Genus “Heloderma”
Numbers represent common ancestors of the subspecies.
Lines represent shared traits.
4. Suggest a shared trait for the line indicated:
Another way to visualize a cladogram is with a Venn diagram. This is a nested set of circles where each group within the circle has the characteristics of each circle. An OUTGROUP is a single organism that sits outside the diagram.
Feathers: cardinal
Backbone: lizard
Outgroup: spider
Talons: eagle
5. Match the trait with the letter:
backbone ___
talons ___
*heterotroph ___
feathers ___
Note: Eagles have talons, feathers, and a backbone.
*A heterotroph is any organism that consumes food, all animals are heterotrophs.
The more organisms included in the cladogram, the more complicated it becomes. A chart may be useful for organizing shared traits.
6. Complete the chart indicating characteristics shared for each group. X indicates group has the trait, O for groups that do not have the trait. (The 4-chambered heart column has been completed for you.)
| Vertebrae | Tetrapod� (4 limbs) | Claws/Nails | 4 chambered heart | Hair / Fur | Opposable Thumb |
Fish | | | | O | | |
Frog | | | | O | | |
Lizard | | | | O | | |
Bird | | | | X | | |
Rabbit | | | | X | | |
Human | | | | X | | |
The lines indicate a trait that is shared by each group in the diagram.
8. What trait is shared by ALL groups on your chart?
7. What trait is only found in ONE group?
Only one group has this trait.
Fish
Frog
Lizard
Bird
Rabbit
Human
vertebrae
tetrapod
claws/nails
4 chambered heart
fur / hair
thumbs
9. Complete the cladogram by dragging the labels to the correct spot.