300 million years ago, your great ancestor had a head like a shark's

When looking at any living creature, you should ask yourself two things: Does it have a jaw? Does it have a spinal column? If the answer to these questions is yes, then you share a common ancestor with it — a very distant common ancestor, but a shared one, nonetheless. Now, research findings published in this week's… » 6/14/12 5:00pm 6/14/12 5:00pm