�黨�ǿ���Ƶ

�黨�ǿ���Ƶ Director and Research Associate are quoted in this story.

There seems to be no ideal number of legs. Humans have two, dogs have four, insects have six and . So what made spiders settle for eight legs?

"I think the best answer and the simplest answer is that spiders have eight legs because their parents did," , an assistant professor of invertebrate paleontology at the State University of New York at Fredonia, told Live Science. "But then that gets into sort of a regress, and somewhere this all had to start."

If we follow the succession of eight-legged spider parents back to about , during the middle Cambrian Period, we arrive at the root of the chelicerate lineage, the group of arthropods that contains spiders. If we go even further back, to , we find the ocean-dwelling lobopods, the ancestors of all arthropods.