245 million years ago (a good 14 million years before dinosaurs would bother showing up), a group of reptiles was thinking about giving up the whole "living on land" thing. They'd been pulling their no-longer-buoyant weight for 135 million years, ever since their amphibious ancestors lost control of a game of "who can go the longest without turning into a dessicated skeletal husk?"
After that many millions of years, it seems those warm wet ocean waves were once again looking pretty dang good.
Enter Atopodentatus, the freakiest-looking reptile this side of Fran Sinclair. This 2.75 meter-long animal was an aquatic in-betweener . . . like a Triassic walrus, it likely spent most of its time in water, but still enjoyed the occasional foray back onto land. It had hoof-shaped claws on its toes, and it still had its hips fused to its spine (like a land-reptile), not the free-moving hips of its fully-marine plesiosaur and pliosaur cousins.
But the part you might have noticed in the (anatomically-rubbish) drawing above is the face. Yes, Atopodentatus had a freaky-weird look about it, the mainly because its whole face is a squashed-in shovel/zipper toothy nightmare.
Fig. 1 from Cheng, L., Chen, X., Shang, Q., Wu, X. 2014. A new marine reptile from the Triassic of China, with a highly specialized feeding adaptation. Journal Naturwissenschaften. doi: 10.1007/s00114-014-1148-4
Why did it have a freaky-weird shovel/zipper? Well, the authors who described it rightly point out that the teeth are far too fragile to have caught anything that might fight back. And so, like a cross between a bulldozer, a backhoe and a humpback whale, Atopodentatus may have shoveled up mud and sand from the seafloor, straining it through 700-ish needle-teeth, leaving only delicious tiny animals behind.
To be swallowed. It filtered them out of the mud so that it could eat them. Just wanted to make sure that part was clear.
I drew the top picture myself, but it really doesn't do the creature justice. Nor does it do basic anatomy justice. Or art. It's terrible. So for your edification and enjoyment, here are a couple of better-drawn renditions of Atopodentatus, with links to the artists' websites.