Sawfish Conservation

A Fish Tale: Sawfish Fact and Fiction Through History
By M. Burger




Myth #3) Sawfish are the only known species with a "saw"

False. Throughout millions of years, elongated rostra with lateral teeth evolved independently at least three times. Sclerorhynchids, an extinct family of sawfish, first evolved in the Cretaceous period. Existing sawfish species belong to the Pristidae family, and are a type of ray. Pristiophorids, or sawsharks, are a distantly related shark species that also wield a toothed-rostrum.

Coevolution of rostra is believed to have occurred because the adaptation is advantageous for feeding. Sawfish have canals that run the length of their rostra that make up what is known as the lateral line system. This is a sensory system that only functions in aquatic environments and serves to detect currents and waves produced from nearby objects or animals. Ampullae of Lorenzini-pores concentrated along the length of the rostrum- function to detect electrical fields emitted by prey. So, the rostrum can act like a metal detector to seek out food items above or below the snout. Within the seven extant species of sawfish, P. microdon is the only species believed to use their rostrum to dig in muddy or sandy substrate for prey. This is hypothesized because they have non-pored lateral line canals (versus pored canals in the other six species), which would prevent substrate particles from intruding.

Another difference in saw morphology between sawfish and sawsharks is that sawsharks have teeth that are replaced in a conveyor belt-like fashion if lost. Sawfish instead have lateral teeth that continually grow from a root. If the tooth breaks at the pulp, it may no longer maintain the ability to re-grow.



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