Two fossils of sea turtles found 160 years apart are pieces of the same animal, researchers said.

Atlantochelys mortoni is an ancient species of sea turtle. Very little is known about the animal as few fossils have been found. They lived during the Late Cretaceous era, which ended with the extinction of the dinosaurs 65 million years ago. 

In 1849, archeologists discovered a piece of a humerus or upper arm bone from the species. The specimen was sent to the Academy of Natural Sciences of Drexel University. This was the distal half of the bone, located nearest the elbow. 

Gregory Harpel, an amateur paleontologist, was out hunting for fossil teeth near a brook in Monmouth County, New Jersey when he spotted an unusual object in a grassy embankment. At first, Harpel thought he was looking at a strangely-shaped rock. It was only when he found marks he believed to be bite marks from a shark that the amateur scientist suspected he was looking at a fossil. 

Harpel dug up his find and sent it to Drexel which held the original find. Ted Daeschler, vice president of collections at the museum, realized the new find was the lower humerus or proximal end of the bone missing from the 19th Century discovery. The two pieces were placed together, and the fractures on each specimen perfectly fit the other showing the two finds were from the same animal. 

"We said, 'no - that can't be!' We even turned them around trying to show they didn't match, but they're obviously supposed to be together," Daeschler told BBC News.

Layers of sediment in which these fossils were found indicate the animal lived somewhere between 70 and 75 million years ago. At that time, the area was populated with sharks and a type of animal known as mosasaurs. 

One discovery from this accidental discovery is the remarkable size of the animal. When both halves of the humerus were placed together, the bone measured 21 inches long. That means Atlantochelys mortoni grew to over ten feet in length, making it one of the largest sea turtles that ever lived. This may be as large as turtles are capable of growing given their body design. 

Most archeologists believe most fossils decay after just a few years or decades of weathering. However, the newest find was exposed to the elements for over 150 years without significant wear. This could provide evidence that other fossils may also survive wear due to weather. 

Analysis of the ancient sea turtle is profiled in the Proceedings of the Academy of Natural Sciences of Philadelphia.