The Fish With a Guillotine for a Mouth 🦈🪓 Before sharks became the kings of the ocean, this was the nightmare lurking in the deep. Meet the Dunkleosteus. It ruled the seas during the Devonian Period, about 360 million years ago—long before the first dinosaur walked the earth! If you look closely at its mouth in this clip, you’ll notice something strange: it doesn't have actual teeth. Instead, it had two pairs of massive, razor-sharp bony plates that self-sharpened every time it closed its jaw.