Answer
This is at least strong evidence of natural selection favoring the evolution of heads around 530 million years ago— perhaps there was some common selective factor, such as the recent evolution of new predators, which made having a head advantageous.
Work Step by Step
The key here is to see that the evolution of heads in multiple lineages all at once points to some common factor, but this one example doesn’t prove that a head is always favored by natural selection.
