Explanation of Figure 7.9 and Figure 7.10 in NCERT Page No. 138 and 139 of Evolution Chapter

Figure 7.9 and Figure 7.10 in NCERT Page No. 138 and 139 of Evolution Chapter depict the evolution of horses from their earliest forms to their present-day descendants.

Figure 7.9: Evolution of Horses

The figure shows the evolution of horses from their earliest forms to their present-day descendants. The following are the stages of evolution:

1. Eohippus (50 million years ago): It was the earliest ancestor of horses. It was about the size of a small dog and had four toes on the front legs and three toes on the hind legs.

2. Mesohippus (35 million years ago): It was the next stage of evolution. It was slightly larger than Eohippus and had a longer snout and a more complex set of teeth. It had three toes on the front legs and three toes on the hind legs.

3. Merychippus (17 million years ago): It was the next stage of evolution. It was the first horse to have only one toe on each foot. It was about the size of a pony and had a more robust body.

4. Pliohippus (5 million years ago): It was the next stage of evolution. It was larger than Merychippus and had longer legs. It had a single toe on each foot and was one of the first horses to have a complex digestive system.

5. Equus (present day): It is the modern horse. It has a single toe on each foot and is the fastest land animal. It has a highly developed digestive system and is well adapted to grazing.

Figure 7.10: Evolution of Whale

The figure shows the evolution of whales from their land-dwelling ancestors to their present-day aquatic forms. The following are the stages of evolution:

1. Pakicetus (50 million years ago): It was the earliest ancestor of whales. It was a land-dwelling animal that looked like a wolf.

2. Ambulocetus (49 million years ago): It was the next stage of evolution. It was a semi-aquatic animal that had webbed feet and was able to swim.

3. Dorudon (40 million years ago): It was the next stage of evolution. It was a fully aquatic animal that had a streamlined body and a tail for swimming.

4. Basilosaurus (35 million years ago): It was the next stage of evolution. It was a fully aquatic animal that was the largest predator of its time. It had a long, flexible body and a small head.

5. Modern whales (present day): They are fully aquatic animals that have a streamlined body and a tail for swimming. They have a highly developed sonar system and are well adapted to life in the ocean.

In conclusion, Figure 7.9 and Figure 7.10 in NCERT Page No. 138 and 139 of Evolution Chapter provide a visual representation of the evolutionary history of horses and whales. These figures help in understanding the complexity of evolution and how organisms have adapted to their changing environments.