for most of this long period of time, there were a number of horse types (genera). now, however, only one genus exists: the modern horse, "equus". it has teeth which grow all its life, hooves on single toes, great long legs for running, and the animal is big and strong enough to survive in the open plain. horses lived in western canada until 12,000 years ago, but all horses in north america became extinct about 11,000 years ago. the causes of this extinction are not yet clear. climate change and over-hunting by humans are suggested.