Counting 46 eyes, the two animals are:

46 ÷ 2 = 23 (only)

Suppose all monkeys have feet:

23× 4 = 92 (only)

Much more than the actual situation:

92-72 = 20 (only)

The red-crowned crane is:

20(4-2)= 10 (only)

Monkeys have:

23- 10 = 13 (only)

A monkey has four feet, and a red-crowned crane has two feet.