Over 160 years ago scientists discovered half of a fossilized bone belonging to a enormous ancient sea turtle. In an amazing turn of events, a paleontologist named Gregory Harpel stumbled across its other half whilst fossil hunting for shark teeth in Monmouth County, New Jersey, but first mistook it for a big rock. After realizing it was a fossil, Harpel took it along to the New Jersey State Museum for further investigation. 

The curators of natural history at the museum Jason Schein and David Parris thought the fossil looked familiar, and started joking about whether it could be the other half of a fossilized humerus (arm bone) from a sea turtle species called Atlantochelys mortoni, which was first described in 1849 and kept at Drexel University's Academy of Natural Sciences, Philadephia. Coincidentally, or perhaps not, the fossil at Drexel University was the upper half (nearest to the shoulder) of a humerus bone; this new fossil was the lower half of a humerus bone (nearest to the elbow joint). Thinking this was all a bit too spooky, Schein decided to bring the fossils together to see if they were a match. 

"When we put the two halves together, we were flabbergasted," Drexel University's Dr Ted Daeschler told the BBC. "We said no, 'that can't be!' We even turned them around trying to show they didn't match, but they were meant to be together." 

The fossils are from a huge turtle, similar to a modern day loggerhead, named A. mortoni​, which lived during the Cretaceous period around 70 to 75 million years ago. The presence of a whole bone meant that they could finally size the animal, calculating that it was probably around 3 meters, or 10 feet, in total length; much bigger than any sea turtle in existence today. The results are going to be published in the forthcoming issue of the Proceedings of the National Academy of Sciences Philadelphia. 

Check out more in this YouTube video from Drexel University.