1. Evolutionary History and relationships
8th grade

2. Accessing Prior Knowledge

3. Animal Limb Research Activity

4. Homologies:
The fossil record is not the only evidence that supports the common ancestry of organisms.
Homologies which are similarities in characteristics between two organisms because they originated from a common ancestor, also support the common ancestry of organisms.
A homologous structure is something that is similar in position, structure, or evolutionary origin.

5. Anatomical Homologies
Species with common origins (ex., birds, reptiles, and mammals) all show similar patterns of anatomy, such as those in the bones of the forelimbs.
Anatomical homologies are similar anatomical structures that exist between species and can be identified as a link to a common ancestor.

6. Asian & African Elephant, Wooly Mammoth
How do all three look the similar?
How are all three different?

7. An example of anatomical homologies exist between modern Asian and African elephants, and the now-extinct wooly mammoth.
All three are distinct species, but they belong to the same family of organisms (Elephantidae) that has large skeletons, trunks, and tusks.
These similar features indicate relatedness among the organisms.

8. Mammals
Mammals are a class of organisms that all share certain traits like breathing air, having hair or fur, and producing milk for their young.
All mammals show similar patterns of bone structures in their forelimbs.
However, mammals also show forelimb similarities to birds and reptiles

9. DSQ 1. How are the limbs of animals similar to each other?
2. How are the limbs of animals different from one another?
3. How are rats similar to elephants?
4. How are rats different from elephants?
5. Could rats and elephants have come from a common ancestor?

10. How are the limbs of animals similar to each other?
They tend to have four limbs, with bending joints, such as knees.
How are the limbs of animals different from one another?
The length, proportion, and range of motion are different.
How are rats similar to elephants?
They are both mammals. They are both vertebrates. They both live on land.
How are rats different from elephants?
Rats are much smaller. The elephant has a trunk.
Could rats and elephants have come from a common ancestor?

11. Rats and Elephants: Similar or Different?
Some might argue that elephants and rats have nothing in common. After all, it is not difficult to find several differences between the two species. Surprisingly, elephants and rats actually do have some structures that are common. A homologous structure is something that is similar in position, structure, or evolutionary origin. Homologies, or similarities in characteristics, between two organisms support the idea of a common ancestry of organisms.

12. Procedures
1. Place the picture of an elephant skeleton and a rat skeleton side-by-side in front of you.
2. Color each of the same bones in the elephant and rat skeleton the same color. For example: color the femur of the elephant and the femur of the rat red. You do not have to do both the right and left of each bone.
3. Once you have colored the bones that both elephants and rats have in common, trim the page and glue it into your lab journal. Title the page “Evidence of a Common Ancestor.”
4. Answer the questions below in your lab journal.

13. Questions
1. Were the bones with the same name in similar places on both the elephant and rat skeleton?
2. Did either the rat or elephant skeleton seem to have extra bones?
3. Write a statement comparing the likeness of the rat and elephant skeleton.
4. Could you infer that the elephant and rat once had a common ancestor based on their skeletons? Why or why not?

14. Skeleton Sort Activity
Ever wonder how a dog evolved from a wolf? Or how a horse has changed over time? By studying fossils, we can learn how a species has changed to adapt to its environment. A paleontologist is a scientist who studies fossils and tries to identify the age and species of these organisms. In this activity, you act as a paleontologist and try to determine the chronological order of a series of skeletons.

15. Procedures
1. Place the cards with the series of horse skeletons or dog skeletons in front of you on your desk. Evolutionary History and Relationships Evidence of Common Ancestry and Diversity
2. Try to arrange them in chronological order – meaning from the earliest species to the most current species. When complete, have your teacher check to see if you are correct.
3. When you have sorted them correctly, write a paragraph in your lab journal about how the organism has changed over time.
4. Switch your cards for the second set and repeat steps 1-3.
5. Answer the questions below in your lab journal.

16. Questions on Skeleton Sort
1. What similarities did you notice in the horse skeletons over time?
2. What similarities did you notice in the dog skeletons and images over time?
3. What other tools or information could help you determine that these species are ancestors of the horse and dog?
4. Early horses lived in jungle areas with soft, wet ground. Eventually they moved out of the jungle onto the drier grasslands and steppes. Observe the pattern of the horse’s toes. Identify the cause and effect of this change.
6. What patterns can be used to identify the ancestry line of an organism?