Vandoo,
I have lurked on the form for years, but now that I have retired from Active Duty, I can play a bit more!
Polynesian are not my area of expertise (not sure if I have one), but have a great interest in the Polynesian cultures and have been able to see some great collections of weapons and artifacts.
That said the wood (from the photo's) almost looks like Koa (Acacia Koa) or Kauila (Alphitonia Ponderosa) (both Koa and Kauila look similar) native to the Hawaiian Islands.
There are several different shark toothed weapons used in the Hawaiian Martial art of Lua. The most often pictured is a leiomano/Palau Papa Niho Mano (paddle shaped/oval mirror shaped with teeth around the outside), however there are several other shark toothed weapons that I am unaware of the true name for but are referred to as knuckledusters. These were weapons and only used as such from my reading (again, not intensive).
The Maori also utilized a shark toothed knife called a Maripi...every specimen of these I have observed is very heavily carved in the Maori style.
The specimen you have recently acquired looks as if it slips over two fingers with the rest of the curved guard if you will, protects the other two fingers...just my tow cents for what it is worth...neat piece! Congrats!
Respectfully,
John