The reassembled upper right arm bone of Atlantochelys.
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Photo courtesy Jason Schein.
The reassembled upper right arm bone of Atlantochelys.

Fossil of Giant Turtle Atlantochelys Reunited With Its Other Half After 163 Years

Exposed fossils are not usually long for this world. Baked in the sun, battered by rain, and scratched by wind-blown sediment, gorgeous bones can quickly crumble into an irreparable pile of shards. Yet this fate is not always inevitable. Along a riverbank of New Jersey, an amateur fossil hunter discovered a lump of bone that turned out to be the missing half of an iconic Cretaceous turtle collected over a century and a half earlier.

While forests and parking lots complicate searching for fossils in New Jersey, there are a few productive spots hidden away among the developments. Among them is the Monmouth Brooks – a place where fossils laid down over the past 66 million years have eroded out of their respective layers and then washed together in point bars along the streambed. Here, pieces of marine reptiles that cruised the seas at the end of the Age of Dinosaurs can comingle with the remains of Ice Age beasts.

Avocational paleontologist Gregory Harpel was looking for such prehistoric treasures as he searched the Monmouth Brooks during a collecting trip in the autumn of 2012. He was primarily after shark teeth, but he spotted a strange chunk on a grassy embankment near the stream. The geologic curiosity turned out to be a prodigious hunk of bone, but what from, Harpel wasn’t sure.

Harpel brought the find to paleontologists at the New Jersey State Museum in Trenton. Natural history curator David Parris immediately recognized the fossil as something very special. The bone had the anatomical hallmarks of the lower part of an enormous turtle’s upper arm bone – the humerus – and, moreover, it was similar to a unique fossil picked up 163 years earlier.

In 1849 the famous naturalist Louis Agassiz named the extinct sea turtle Atlantochelys mortoni from a fossil held at Philadelphia’s Academy of Natural Sciences. Agassiz didn’t have much to go on – just the upper portion of the turtle’s humerus – but the fossil was distinctive enough to merit establishing a new genus and species. No other definite bones of the 75 million year old turtle turned up after that. The fragment sat alone until the day Harpel brought his curious find to Parris, assistant curator Jason Schein, and registrar Rodrigo Pelligrini.

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David Parris holds Atlantochelys. Photo courtesy Jason Schein.

“When I first saw the fossil,” Parris says, “it reminded me of Atlantochelys primarily because of the very large size and narrow shaft.” And since this was another chunk of upper arm bone, he quipped to his colleagues that perhaps Harpel had found the long-lost match for the Agassiz’s original specimen. Such a chance was unlikely. Everyone knew that fossil bones break down so quickly that the other part of the original Atlantochelys likely disintegrated years ago. Nevertheless, Schein and Pelligrini traveled to the Academy of Natural Sciences to compare the bones and confirm whether or not Harpel had found another Atlantochelys.

The fossil wasn’t just another Atlantochelys bone. The piece was part of the very same one. “The break between the specimens occurred at mid-shaft and the broken surfaces fit like puzzle pieces,” Parris and colleagues write in the paper documenting the find.

“My reaction then, as it still is, was nearly complete disbelief,” Schein says. “The odds are infinitesimally minute” for such a clean match, he explains, so much so that other Academy paleontologists were called in to get their reaction to make absolutely sure that the fit couldn’t be a fluke. There was no doubt about it – Harpel had discovered the missing half of the original Atlantochelys bone.

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A hypothetical restoration of Atlantochelys by Jason Poole.

The only way that the find could have been better is if more of Atlantochelys magically appeared. So far, the reuinted humerus is the sole representative of the turtle. What happened to the rest of the skeleton is a frustrating puzzle, Schein says, although tooth-marks left by sharks on the arm bone hint that some scavenger’s hastened the marine reptile’s disassembly.

Then again, perhaps there’s more of Atlantochelys scattered among the New Jersey point bars. If more giant turtle bones turn up in the same stretch of stream, and researchers now know that such bones can withstand exposure for over a century, there’s a chance that they might have come from the same animal. “I think it highly likely that other large turtle bones from the vicinity will be the same individual, and it’s also probable that other individual Cretaceous fossils from the brooks could be similarly grouped,” Parris says.

Atlantochelys may even have a role to play in the burgeoning debate over commercial fossil hunting in America. Commercial outfits often like to claim that they are saving fossils that are exposed and in danger of rapid destruction by the elements. “The fact that the other half of this Atlantochelys bone was at or near the surface for at least 163 years really pokes holes in that line of reasoning,” Schein says.

At the same time, the discovery underscores the vital relationship between museums and amateur experts in recovering and preserving our planet’s prehistoric history. That the missing piece of Atlantochelys should be found after so long is the stunning outcome of luck, scientific scrutiny, and cooperation.  “To say this is a once-in-a-lifetime event is really short-changing it,” Schein says, “This is completely unprecedented.”

Reference:

Parris, D., Schein, J., Daeschler, E., Gilmore, E., Poole, J., Pellegrini, R. Two halves make a holotype: two hundred years between discoveries. Proceedings of the Academy of Natural Sciences of Philadelphia. 163. ISSN 0097-3157.