A 9-year-old girl from Prince Frederick, Maryland, has made the ultimate paleontological discovery: a 15 million-year-old megalodon tooth.

Molly Sampson, along with her sister, Natalie Sampson, 17, and her dad, Bruce Sampson, went out to hunt "treasure" in a bay near Calvert Cliffs on Christmas Day.

The young girl was ready for the day's fossil hunt because she was able to wear the new insulated waders she had been "begging" for, she told Fox News Digital.

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Molly Sampson and her treasure hunting team left their home at 9:30 a.m. to hunt for shark teeth.

While out in knee-deep water courtesy of her new Christmas waders, she looked over and saw her Christmas miracle: a 5-inch-long megalodon tooth.

Her sister and father went over to see what Molly Sampson was so excited about.

They were amazed by the discovery.

"I am so thrilled about the shark's tooth Molly found," Bruce Sampson told Fox News Digital. 

"Not only because of the size and rarity of the find, but also because of the joy and excitement I get to see in my kids with all of their discoveries."

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"I was so excited, and I kept thinking I was dreaming," Molly Sampson said. 

"It was something I have always wanted to find, and I couldn't believe it."

Bruce Sampson said he was "shocked" by his daughter's "once-in-a-lifetime find."

"Don't get used to it," he said he joked with her. "This is the kind of find every fossil hunter dreams of."

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This is not the first time she's found a megalodon tooth during her fossil hunts — but she's never found one this large.

"I have found five other megalodon teeth, but they are only an inch or two" in size, she said.

"Finding one this big is very rare [and unique] because of how big it is."

When Molly Sampson came home from her discovery, she whispered to her mom, "I know God put that there for me," the family told Fox News Digital.

The family took the prehistoric treasure to Dr. Stephen J. Godfrey, curator of paleontology at Calvert Marine Museum in Solomons, Maryland, to see what information he could share about the creature that once had the tooth.

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"From where she found the tooth along Calvert Cliffs, it is about 15 million years old. So it came from the middle of what geologists would refer to as the Miocene epoch," Godfrey told Fox News Digital in an interview.

Scientists are able to age the sediment in which a fossil is found to then age the fossil itself, along with the presence of "radiometric isotopes" that can be used to "radiometrically age" the sediments in which a fossil is found, Godfrey said.

"Radioactive isotopes change over time," he also said, "and it is that very constant (clock-like) rate of change that can be used to age the sediments and by extension the fossils within."

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Based on the size of the tooth, Godfrey was able to give an estimated size of the creature to which the tooth belonged.

"Molly’s meg tooth would have come from a shark between 45-50 feet long. So, when it shed that tooth, it would not have been as large a megalodon as it could have grown to be," Godfrey said.

"It was a ‘young teenager,’" he said. "The very largest megs are calculated to have been 65 feet long."

Molly Sampson's huge megalodon tooth is the largest in her collection, but it also is one of the largest found in the Calvert Cliffs area, Godfrey said.

Megalodons are "one of the — if not the largest marine macropredator the world has ever known," said Godfrey. 

"Megalodons lived from about 25 million years [ago] to about 2.5 million years ago."

He added, "They shaped [and dominated] the global marine ecosystem, global marine food-webs and the evolution of many different kinds of marine mammals, their preferred prey."

Molly Sampson shared the news of her prehistoric treasure find online — and it has since garnered numerous responses from people all over the world, including India, Spain, France and Germany.

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"I have gotten messages from adults telling me I have inspired them to go outside more and explore," said Molly Sampson.

Molly Sampson has been fossil hunting with her dad ever since she was little. The beaches with cliffs in Calvert County have been a great spot to find prehistoric treasure, the family said.

"I will never stop!" she told Fox News Digital. "I have told my mom I want to collect fossils and study them when I grow up like a paleontologist."

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The girl said she's enjoyed sharing her findings with others on her website and social media account dedicated to her discoveries. 

"I think it's really cool that I am the first human to ever hold that tooth since it was in the mouth of the megalodon," Molly Sampson said.

"When I picked it up, I was the first person to touch it and that is really cool to think about."

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On Jan. 25, Molly Sampson was welcomed to the floor by the House of Delegates of Maryland.

While the legislators were in session, they honored her for her discovery in a House Resolution by the delegates.

The document she received said in part, "The House of Delegates of Maryland offers its sincerest congratulations to Molly Sampson, in recognition of your discovery of a prehistoric megalodon shark's tooth in the Chesapeake Bay."