填Although
有几处小错误,我帮你稍微修改了一下：
Horses, at first, were all wild animals like zebrasare today. Although they first evolved in North America, by the time people were spreading through the world, horses had become extinct in North America.
虽然马最早在人类足迹遍布全球时在北美进化出现,但是后来马在北美绝迹.