Dusky sharks do not live in the Pacific waters near the Republic of Kiribati. Neither do spottail sharks, nor the aptly named bignose sharks. But they used to live there at one point in the past -- right by the Gilbert Islands, according to anthropological evidence. Ancient shark-tooth weapons can serve as a record of past biodiversity, according to new ecological research.

The sharks disappeared before biologists ever knew they were there, according to Columbia University conservation biologist Joshua Drew, who presented his findings at the Ecological Society of America's annual meeting. Drew examined weapons from the Gilbert Islands that are owned by the Field Museum in Chicago, according to Nature.

The collection of swords, tridents and other serrated implements are made of shark teeth twined together, and some date to 120 years ago. Because biologists can identify sharks by their teeth, the weapons can prove which sharks were found in the area where the weapons were made, according to Drew.