Shark-tooth weapons once used for warfare in the Central Pacific have revealed two locally extinct shark species, a new study says.

Historical records show that natives of the Gilbert Islands (map), now part of the country of Kiribati, once battled one another using wooden swords, spears, daggers, and other weapons inlaid with the sharp, jagged teeth of local shark species.

By studying 120 such weapons housed at the Field Museum of Natural History in Chicago, scientists determined that Gilbert Islanders used teeth from at least 17 shark species in making their weapons.

To their surprise, however, the researchers discovered that two of the species—the spotfin shark and the dusky shark—are no longer found in the reefs off Gilbert Island.

"Initially, we just wanted to catalog what shark species were there. We didn't suspect that two of them would be gone," said study co-author Joshua Drew, a biologist at New York's Columbia University and the Field Museum of Natural History in Chicago.

"Had we never done this work, nobody would have ever known that these things ever existed there. It had been erased from our collective memories that these sharks once plied these waters," said Drew. (Also see "Sharks Warn Off Predators by Wielding Light Sabers.")

Both of the locally extinct shark species can still be found in other areas, so it's likely that the Gilbert Island populations were driven to extinction, scientists say.

Armed to the Teeth

The Gilbert Island weapons used in the study date to the mid-19th century, when the first British and American missionaries and whalers arrived at the island. (Read about the pioneers of the Pacific.)

The main bodies of the weapons were made of wood, and shark teeth were painstakingly sewn along their edges using thread made from coconut fiber and human hair. Because the islanders had no metal, they used spiral snail shells to bore holes in the teeth before sewing them to the weapons.

According to written eyewitness accounts by the missionaries, the Gilbert Islanders used the shark weapons in violent and often fatal territorial disputes. "Space on the island was at a premium," explained Drew, whose study was published online April 3 in the journal PLoS ONE.

Often in these battles, two "champions" would fight in a central skirmish. The champions "were dressed in this really cool armor made of very tightly woven coconut cords, and they had tiger shark 'brass knuckles' and helmets made out of dried pufferfish with spikes on them," Drew said.

The champions' weapons might include elaborate swords made of three separate shark-teeth-encrusted blades bound together with stingray skin. Meanwhile, as the champions clashed, their "henchmen" would duke it out in the background, he said.

According to the missionaries, "the henchmen had these really long spears that were completely covered with shark teeth. And while the two main guys were fighting, the henchmen would basically try to reach over their guy and poke the other guy ... so there was this battle of these 15-foot [4.5-meter] spears above the heads of the champions," Drew said.

Women also took part by lobbing clubs at the enemies—sometimes hitting their own warriors.

While sharks were important for the construction of weapons, historical records indicate the Gilbert Islanders weren't killing them just for their teeth. "The ethnographic literature suggests they used all the different parts—for shields, for household [items], and for food," Drew said. (Also see "New Shark Species Found in Food Market.")

"There were social prohibitions about who could eat certain parts of the shark, and you had to go through certain initiations before you could partake in the [shark meat]."

Keeping History Alive

Drew and his team are currently seeking funding for another project to create an archive of the written and oral records of living Gilbert Islanders about their island's ecology before it disappears completely. (See pictures of the Pacific Islands.)

"The Gilbert Islands are threatened by climate change, and we're not sure if they'll still be habitable in a hundred years," Drew said. "If the islanders are moving to Australia or other areas ... they're going to be severed from their generations-long contact with the reef and its organisms."

The scientists also hope that the knowledge about which shark species the Gilbert Islanders used to make their weapons will help guide future conservation efforts in the region.

"It's not too late. There are still sharks in those waters. Shark populations take a while to regrow, but they can," Drew said.