Why did many odd-toed ungulates become extinct? There were a lot of odd-toed ungulate animals in the ancient times but now just few of them survived. What is the reason for that?

there are two suborder under perissodactyla that are still suvival, Hippomorpha and Ceratomorpha. many perissodactyla species become extinct may bacause the member of perissodactyla animals have sample stomach, compared with artiodactyla, so after the plant change on the earth, they cannot adapt it. and also hinting was one part of reason. <