We camped there, where the loam was trampled by countless herds of bison.我们在那里露了营。那里的壤土遭到无数群野牛的践踏。Our ancestors ochred pictures of bison on their cave walls.我们的祖先用赭色在洞穴墙壁上画了野牛图。There are two subspecies of bison in North America.北美洲野牛有两个亚种。The breeders crossed the bison with domestic cattle.养牛人使野牛与家牛杂交繁育。