With the complete 21-inch bone in hand, scientists at the state museum and the academy, which is part of Drexel University, were able to estimate the size of the massive reptile. Their calculation: 10 feet from head to tail, as much as twice the length of its typical modern counterpart. Atlantochelys mortoni swam in shallow ocean waters covering what is now New Jersey more than 70 million years ago.
Jason Schein, a colleague of Parris' who brought the "new" bone piece to the academy for comparison with the original fragment, said he is still recovering from the shock.
"To say that it's a once-in-a-lifetime experience would be short-selling it," Schein said.
Academy records are unclear about when and where the first half of the bone was found. When it was described in an 1849 paper by Louis Agassiz, a prominent 19th-century biologist, the fossil had already been in the collection of the Philadelphia museum for some time. Of its origin, Agassiz wrote only that it had been found in New Jersey.
Amateur fossil hunter Gregory Harpel, of Oreland, Montgomery County, found the other half in 2012 in Monmouth County along the banks of Big Brook, which winds between Marlboro and Colts Neck Townships.
Harpel, 54, an analytical chemist, said he had been visiting the brook for several years to collect prehistoric shark teeth. He found the bone in the fall of 2012, though he did not know exactly what it was.
"Initially, I thought it was just a stream rock," Harpel said. "The more I looked at it, it had a definitive shape to it."
Harpel then saw that the rock was porous, like the surface of bone. So he took it to the New Jersey State Museum one day after work.
The next step in the improbable tale needed the expertise of Parris, renowned among colleagues for his steel-trap memory. Parris recalled seeing the other bone piece in Philadelphia 25 years earlier.
Schein took it to the academy a few months later. He looked at the two segments side by side with academy scientists Jason Poole and Ned Gilmore, and they could hardly believe it. They went across the hall to get another opinion from Edward B. "Ted" Daeschler, associate curator of vertebrate zoology, and fossil preparator Fred Mullison.
"It was Jason, Jason, Ned, Ted, and Fred," Schein recalled. "I tell people it was like a Dr. Seuss book."
The collective view? Same turtle, no doubt.
"Believe me, we tried to sink it," Daeschler said.
In addition to the dimensions of the two halves and their fit, the case was further cemented by similar tooth marks on each piece - evidence that the reptile had been "disarticulated" by a hungry shark, Daeschler said.
Also contributing to the research was Rodrigo A. Pellegrini, a paleontologist at the museum in Trenton.
Harpel later went back to Big Brook to show Schein and Parris where he found the bone fragment. They were not immediately able to find any more turtle bones.
But by analyzing the sediment and other fossils found at the site, the scientists concluded that the turtle bone was first buried during the Cretaceous period - a hot, muggy time when much of New Jersey was covered by water. They think the bone later broke when the soil eroded, and the two pieces were redeposited apart from each other.
It is not the first time that two parts of a fossil bone have been found separately and reunited, but generally they are found at about the same time, Daeschler said. On occasion, fragments have ended up in different collections until someone realizes years later that they belong together.
But Harpel's chance discovery on a stream bank, perhaps two centuries after the other bone piece was found, is one for the ages.
He donated the fossil to the state museum, while the other half remains in Philadelphia.
This week, the Trenton museum is putting a cast of the two pieces on display, alongside the corresponding but much smaller bone, less than half as long, from a modern loggerhead turtle - its closest present-day relative.
Harpel said he is thrilled.
"It's all fate and circumstances that drew me to find it in the first place," he said. "It belongs to the public. It doesn't need to be sitting in a drawer in my house."