1. Modern Evolutionary Classification
Chapter 18.2

2. Dichotomous Key
Used to identify objects or organisms that have already been described by another scientist.
“di”- means two
Each is made up of paired statements.
As you go down step to step, the classification is narrowed down until all organisms have been identified.

3. Sample Dichotomous Key for beans
1a. If the bean is round…it is a garbanzo bean. 1b. If the bean is oblong…go to step 2. 2a. If the bean is white…it is a white northern bean. 2b. If the beans is dark-colored…go to step 3. 3a. If the bean is a solid color…go to step 4. 3b. If the bean is speckled…it is a pinto bean. 4a. If the bean is black…it is a black bean. 4b. If the bean is reddish-brown…it is a kidney bean.

4. Cladistics is classification based on common ancestery.
To classify species on how they are related, scientists must look at more than just physical traits.
Modern classification is based on figuring out evolutionary relationships using evidence from living species and the fossil record.
Phylogeny: evolutionary history for a group of species.
can be shown as branching tree diagrams.

5. Phylogenic Tree

6. Cladistics Cladistics: classification based on common ancestry.
Goal: to place species in the order in which they descended from a common ancestor.
Cladogram: evolutionary tree that proposes how species may be related to each other through common ancestors.

7. Cladogram

8. Cladistics/Cladogram
The root words of cladistics and cladogram is “Clade”.
Clade is a group of species that shares a common ancestor.
For example: the glyptodon is the common ancestor of about 20 modern species of armadillos.
Together, the glyptodon and all of its descendents form a clade.

9. Steps in Building a Cladogram draw from page 517
1. Cladograms are diagrams showing how evolutionary lines or lineages, split from each other over time.
The point of “splitting” is called a node.

10. Steps in Building a Cladogram draw from page 517
2. How recently lineages share a common ancestor reflect how closely they are related to one another.
Lineages 3 and 4 are more closely related than any other.

11. Steps in Building a Cladogram draw from page 517
3. Shows the evolutionary relationships among vertebrates, animals with backbones.

12. Interpreting a Cladogram
Main features of a cladogram:
Derived characters
Nodes
Identifying clades

13. Derived Characters 1. Derived characters:
a trait that arose in the most recent common ancestor or a particular lineage and was passed along to its descendants.
shown as hash marks --- between the branches of the cladogram.

14. Nodes 2. Nodes: Each place where a branch splits.
Represents the most recent common ancestor shared by a clade.
How many nodes are in the cladogram handout? 5

15. Identifying clades 3. Identifying clades:
You can identify clades by using the “snip” rule.
Whenever you “snip” a branch under a node, a clade falls off.
If you “snip” below the node where turles and tortoises branch off, you would be left with which clade?
Reptilia clade

16. Closing/Homework “Cladogram Analysis”
In your lab groups of 3-4, work on the worksheet together.
Due Monday 2/27