In Cephalopods
Most cephalopods possess a radula as well as a horny chitinous beak, although it is reduced in octopuses and absent in Spirula.
The cephalopod radula rarely fossilizes: it has been found in around one in five ammonite genera, and is rarer still in non-ammonoid forms. Indeed, it is known from only three non-ammonoid taxa in the Palaeozoic era: Michelinoceras, Paleocadmus, and an unnamed species from the Soom Shale.
Read more about this topic: Radula