Helicoprion, shark dead since about 225 million years ago (Triassic sometime). It didn't lose its teeth like other sharks did (which, in their case, is *constantly*), but had them grow in a continual spiral. Paleontologists aren't sure how the spiral teeth were configured in the jaw nor how they were used.
жесть блин. всегда говорил, что фантазия природы неисчерпаема.