The ancient shark, which belongs to the family of shark fin sharks, has been discovered among thousands of fossil fragments and teeth. The shark was named Isogomphodon aikenensis after Aiken prefecture, where the species was found. The discovery was led by researchers Dave Cicimurri and Jim Knight of the South Carolina State Museum in Columbia. Mr. Cicimurri is the current curator of the museum of natural history and Mr. Knight is his predecessor.
Aiken Prefecture sits on the southwestern border of South Carolina, more than 100 miles (160 km) from the Atlantic Ocean.
But 30 million years ago, the area would have been watered by 20ft to 30ft (6.1m to 9.1m) of salt water.
The conditions would be perfect if prehistoric sharks, crocodiles and turtles thrived.
The researchers presented their shark discovery in the revised PaleoBios magazine.
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Mr Knight told the Aiken Standard: "Whenever you can increase the knowledge of paleobiodiversity, it is exciting.
The shark typically only grows to about 4.5 feet (1.5m) long.
The prehistoric dagger would have been similar in size in adulthood, reaching up to five feet (1.52 m) in length.
The shark's teeth were very short and thin, only a little over a quarter of an inch high, giving them a seam-like appearance.
According to Cicimurri, the teeth would be useless for extracting pieces of flesh from the sharks' prey.
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He said: "It probably ate small fish and took them with its small needle teeth.
"Then it dropped them. It didn't buy its food. "
The ancient daggernose is the first of its kind discovered on the planet.
But Mr. Cicimurri said more fossils of the aikenensis are likely to be found in other parts of South Carolina, Georgia, Alabama and Mississippi.
He said: "I wouldn't be surprised if they show up somewhere else."