The story of Gregory Harpel and the ancient turtle fossil he found in Monmouth County, N.J., has shown scientists the natural world can still work in strange and mysterious ways.

Harpel, an amateur paleontologist, knew at once he was gazing at something special when he spotted the fossil, a piece of an arm bone belonging to the rare giant turtle, Atlantochelys mortoni, the only other known sample of which was displayed at the Academy of Natural Sciences of Drexel University in Philadelphia.

The bone, Harpel remembered, seemed strange and out of place amid the grassy embankment that was just upstream from the area he usually hunted for fossils, mainly prehistoric shark teeth.

"I picked it up and thought it was a rock at first -- it was heavy," said Harpel, an analytical chemist from Oreland, Pa., in a news release.

When he realized the bone was likely more scientifically significant than his growing collection of shark teeth, Harpel took it in for evaluation at the New Jersey State Museum, to which he eventually donated the find.

Later on, during the fall of 2012, Jason Schein, assistant curator of natural history at the state museum, was visiting visited the Academy's research collections when he discovered the state museum's turtle fragments appeared to be a pretty good fit with that held by the Academy, which, after the two pieces were reunited, came as a total surprise to all involved.

"I didn't think there was any chance in the world they would actually fit," Schein said in a news release.

The Academy's arm piece was much too old to find a new match, according to the conventional research wisdom.

Paleontologists have long assumed fossils found in exposed rock will be weathered down from exposure to the elements if they aren't collected and preserved quickly, at least within a few years.

So, there was little reason to believe an exposed half of the same old bone would survive in a New Jersey streambed, only to be found relatively intact over 160 years after its other half was unearthed in 1849.

The Academy's older bone was originally named and described by 19th-century naturalist Louis Agassiz as the first-ever specimen of its genus and species. In the following years, it remained the only known fossil specimen from that specific turtle.

Harpel's turtle arm has prompting scientists to realize that, sometimes, fossils can survive long stretches of time, even when exposed.

With the fully assembled A. mortoni humerus, scientists have been able to calculate the animal's overall size -- about 10 feet from tip to tail, making it one of the largest sea turtles ever known.

Scientists believe that the entire unbroken bone was originally embedded in sediment during the Cretaceous Period, 70 to 75 million years ago, when the turtle lived and died.

The story of the fractured turtle arm -- and the insights its reunification have provided -- are told in the Proceedings of the Academy of Natural Sciences of Philadelphia, as well as the April 2014 issue of National Geographic magazine.

"The astounding confluence of events that had to have happened for this to be true is just unbelievable and probably completely unprecedented in paleontology," said Schein.