A surfer who survived a shark attack 25 years ago finally knows the kind of shark that bit him, and it’s all thanks to the small sliver of a tooth extracted from his foot.

A DNA test of the tooth retrieved from Jeff Weakley, who was bitten while surfing at Florida’s Flagler Beach in 1994, was conducted by scientists from the Florida Museum of Natural History. The test revealed that the culprit was a blacktip shark.

Scientists were skeptical that the small piece of tooth would contain viable shark DNA after nearly 25 years. The DNA was heavily fragmented, but intact enough to analyze. (Photo Credit: Florida Museum Photo by Kristen Grace)

“I was very excited to determine the identity of the shark because I’d always been curious,” said Weakley, who was originally planning to turn the small sliver of tooth into a pendant. “I was also a little bit hesitant to send the tooth in because for a minute I thought they would come back and tell me I’d been bitten by a mackerel or a houndfish – something really humiliating.”

Weakley didn’t have to worry. The shark bite was legit: caused by a blacktip shark, Carcharhinus limbatus, a shark species commonly involved in bites in Florida.

Jeff Weakley was a 21-year-old surfer when he was bitten by a shark. It grabbed his foot, which was trailing in the water, and shook it briefly, leaving him with several lacerations. (Photo Credit: Jeff Weakley)

According to Gavin Naylor, director of the shark research program, the fact that any viable DNA was left in the tooth fragment to analyze – after nearly 25 years in Weakley’s foot where it would have been attacked by his immune system – was a shocker.

“I had put our odds of success at slim to none,” Naylor said.

Lab manager Lei Yang holds a pair of blacktip jaws. Blacktips are commonly involved in shark bites in Florida, the majority of which are not life-threatening. (Photo Credit: Florida Museum of Natural History photo by Kristen Grace)

To analyze the DNA from the tooth, laboratory manager Lei Yang cleaned the tooth of contaminants, removed part of the enamel, and scraped pulp tissue from the tooth’s cavity. He extracted DNA from the tissue, purified it, broke it into small pieces, and added molecular “bookends” on either side of each piece.

The bookends made a genomic “library” out of the DNA, which Yang could then search for the sequences he needed to identify the shark. He compared the target sequences against two databases of shark and ray genetic information to determine Weakley had been bitten by a blacktip.

According to Yang, about 70 percent of shark bites are caused by unidentified species, and more precise data on which species are involved could improve bite mitigation strategies.

More on Geek.com: