As amazing as the different species of earth are, there were so many more that are no longer with us. In some cases, that’s fortunate for us, because many were huge and predatory. In other cases, it would be so cool to have them around now. And then there are some that are just too weird to contemplate, like the shark with a circular saw in its mouth and the poop-eating snail that fossilized in place to show how it was done. Emily Graslie of The Brain Scoop guest-hosts this week’s mental_floss video from the Field Museum in Chicago. -via mental_floss