When vertebrates land, there are many different quadrupeds, such as five toes, six toes and eight toes. But in the extinction at the end of Devonian, the 6-toe and 8-toe were extinct. Fortunately, 5-toe has survived and evolved to this day, so all quadrupeds are 5-toed since then, but some specialize in 65,438+0 toes (such as horses) and some specialize in fins (such as dolphins).