Found this on the anthropological collections web site, acquired in '46.
Country: FRENCH CAMEROON?
Material: SAWFISH,CORD
Dimensions: L:69.2 W:14.5 [in CM]
Donor: MAMMALOGY DEPARTMENT
It brings up two points, it was not originally collected as a weapon, as the donor was the MAMMALOGY DEPARTMENT.
Secondly, Sawfish must be Mammals
