Question

the mesohippus is the same species as the modern horse.
there were no animals that would be considered to be related to horses 55 - 50 million years ago.
horses appeared no more than a million years ago and had no ancestors before that time.
the modern horse is related to other extinct species.

Explanation:

1. Analyze the first statement: Mesohippus is an extinct species, and modern horse is Equus. They are not the same species. So this statement is wrong.
2. Analyze the second statement: The figure shows Hyracotherium (55 - 50 mya) which is related to horses (as it's part of the horse evolution lineage). So this statement is wrong.
3. Analyze the third statement: The figure shows horse - like species (e.g., Hyracotherium) existed before 1 mya, so horses had ancestors before 1 mya. This statement is wrong.
4. Analyze the fourth statement: The figure shows a lineage from Hyracotherium to Mesohippus, Merychippus, Pliohippus, and finally Equus (modern horse). So modern horse is related to these extinct species. This statement is correct.

Answer:

The modern horse is related to other extinct species.