Band 9: The diagrams below show the development of the horse over a period of 40 million years. Summarize the information by selecting and reporting the main features, and make comparisons where relevant.

The diagram illustrates how horses have evolved over the past 40 million years.

Overall, horses gradually increased in size and experienced significant changes in the structure of their feet, particularly in the number of toes.

Looking first at the earliest stages of evolution 40 million years ago, the Eohippus horse initially had a relatively small body and four toes of equal size on each foot. This was followed by Mesohippus, which appeared 30 million years ago. It was noticeably larger than its predecessor and had three toes instead of four, with the middle toe being more prominent than the two outer ones. Eventually, Eohippus evolved into Mesohippus, showing noticeable changes in both body size and toe structure.

Turning to the later stages of evolution, Merychippus appeared approximately 15 million years ago. Compared to Mesohippus, its middle toe had decreased in size, whereas the two outer toes had become slightly larger. Additionally, its overall body size increased considerably, a development continued in the modern horse, which eventually evolved to have a single hoof on each foot.