Rostral denticles refer to the jagged spikes that run along the snouts of sawsharks and sawfishes. They are typically used in foraging and self-defense.'Rostral denticles are believed to be modified scales because of their location on the elongated snout, and they have an external morphology and developmental pattern that's similar to scales,' said Cook, explaining that, just like with scales found elsewhere on the body, for a new rostral denticle to form, an old one must first fall off and make a space available.

https://interestingengineering.com/science/sawfish-hold-secret-how-teeth-evolved

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