A man found a giant megalodon tooth that experts say belonged to a shark the size of a semi-truck

• A charter boat captain found a whopping 6.25-inch long megalodon shark tooth in Florida.
• The tooth probably belongs to a giant megalodon that would have measured around 50 feet in size.

Florida was a very different place millions of years ago. Many parts of the region were completely submerged, and the waters were infested with giant, ancient sharks including the megalodon — the largest sharks that ever lived.

That's why today, the Sarasota County coastline in Venice, Florida, is known as the shark tooth capital of the world. Recently, a charter boat captain discovered one of the largest fossilized shark teeth ever from a megalodon shark.

One of the largest megalodon teeth ever discovered

Michael Nastasio, who has been hunting shark teeth in Florida for 12 years, discovered a fully-intact megalodon shark tooth that was 6.25 inches (15.87 cm) long — only about an inch smaller than the largest megalodon tooth on record.

The tooth was one of two he recently discovered. The first was less intact and broken from the top. "When I found the second one and it was complete, my mind was blown," Nastasio told The State.

To date, no one has found a complete fossilized skeleton of a megalodon shark. So scientists can only speculate how large a shark with a 6.25-inch tooth would be.

But Jack Cooper, a megalodon researcher at Swansea University, said in this case, "we can instantly say we have a very big shark here."

Megalodon teeth are similar to great white shark teeth, and it's thought the two species may have been close relatives. That's why scientists use great white sharks as a way to estimate megalodon size.

"These methods rely on the relationship between tooth size and body length in the living great white shark to predict the hypothetical body length of the megalodon," Victor Perez, a shark fossil expert and visiting assistant professor of Environmental Studies at St. Mary's College of Maryland, told Insider.

"The tooth here looks to me to be an upper anterior tooth [near the front of the mouth] and so that 6.25-inch size probably translates to a shark that would've been at least 15 meters long, well over 50 feet," Cooper said.

Emma Bernard, curator of the Fossil Fish section at the Natural History Museum in London, further confirmed: "Based on the size of the tooth, it would have belonged to one of the larger megalodons. Estimates have the largest megalodon at about 15 to possibly 18 meters in length. The 15-meter mark is the most appropriate."

These estimates suggest that Nastasio's tooth likely came from a megalodon that was around the size of a semi-trailer.

A megalodon tooth is worth thousands of dollars

Nastasio runs a company named Black Gold Fossil Charters under which he regularly organizes underwater trips for people who want to hunt for shark teeth — either for business or pleasure. Turns out, there's some money to be made in the megalodon business.

"Megalodon teeth are sold and bought, and often for very high prices too. People who buy these teeth tend to be budding scientists or enthusiasts who either have their own private collections or wish to own the biggest tooth they can find," Cooper said.

The price of a megalodon tooth depends on its size, color, and the quality of the fossil, and there are websites where you can find megalodon teeth selling for over $7,000.

The shark experts we spoke with wouldn't put an exact value on the giant tooth Nastasio found, but they hinted that a megalodon tooth this big in size and also complete could be sold for thousands of dollars.

Nastasio has already put some of the shark teeth he found in the past on display for sale in a shark fossil store named Shark Frenzy, but he's not going to do the same for his rare 6.25-inch megalodon fossil, WTSP reported.

He recently told WTSP that he won't sell his biggest shark tooth — he's keeping it for himself.