The precise moment of death, 65 million years ago, is captured in stone. The head and the legs are tucked under the shell, just as a threatened turtle would do today. Nearly intact, the fossil is exceedingly rare.
This Cretaceous specimen recently met modern technology. At the request of scientists at the New Jersey State Museum, veterinarians at Penn Vet’s New Bolton Center used a new robotics-controlled imaging system to examine the turtle.
The fossil is now on display as part of a new Natural History Hall exhibit, “Written in the Rocks,” which opened July 2 at the museum in Trenton.
Museum research associate Jennifer Anné heard about the new imaging system and emailed New Bolton Center’s Dr. Dean Richardson to ask if it could be used to try to see the bones inside the turtle fossil. Typical imaging equipment could not accommodate the large turtle fossil, but New Bolton Center’s revolutionary system is designed with robotic arms that move around the patient, allowing examination of the entire anatomy of horses and other large animals.
“I said we’d be happy to look at it,” said Richardson, Chief of Surgery. “Why wouldn’t I? I love science.”
Richardson set up the scan for June 16, free of charge, “for collegial reasons as a fellow scientist,” he said. “Also, it is, after all, an animal.”
One of the most challenging aspects of imaging with the robotic system is correcting for motion. “I told Jennifer I thought motion with her fossilized turtle wasn’t going to be a problem,” Richardson joked.
Penn Vet is the first veterinary teaching hospital in the world using the EQUIMAGINE™ imaging system, which has clinical and research applications for both animal and human medicine. In collaboration with Four Dimensional Digital Imaging (4DDI), the company behind the system’s innovation, New Bolton Center veterinarians are developing application-related protocols for large animals.
A Turtle Scan
Anné and colleague Brittany Malinowski, brought the fossil to New Bolton Center in the front seat of a Ford Mustang. Getting the 200-pound specimen out of the car was the first challenge, and then onto the platform that usually holds a horse’s head.
“We recruited several members of our barn crew to safely get the turtle onto the gurney,” said Dr. Barbara Dallap Schaer, Medical Director of New Bolton Center, who helped get the fossil out of the car, and facilitated the imaging. “Although we handle valuable patients every day, this was a different matter.”
The computed tomography (CT) scan itself only took only about 30 seconds, the two robotic arms moving around the specimen. The 190-degree, 3-D images show the outside of the turtle, with great detail of the head and the hands. Only one bone inside is visible, the humerus, an arm bone.
“We can see the position of the head and neck, how it is tucked underneath the shell. We can also make out individual neck bones,” said Dr. Chris Ryan, New Bolton Center radiologist, who had never before scanned a fossil.
“We were curious to see if we could see anything inside the fossilized shell, but it was all just dense rock,” he continued, examining the scans. “The most we could see inside was a little bit of the upper arm bone.”
For a CT scan to be successful, there must be differences in the densities of materials, Richardson said. But the inside of the turtle was uniform, the biological materials replaced with minerals over time.
The turtle is of the type with the genus name Basilemys, said Jason Schein, the museum’s Assistant Curator of Natural History. Appropriately, the scientists have named it Basil. They found it in Carbon County, Montana, during the Bighorn Basin Dinosaur Project’s 2013 Field Expedition.
The Expedition is an annual New Jersey State Museum event, combining science with education. Many fragments of turtle fossils are scattered about the area, Schein said. That July of 2013, Malinowski spotted a bit of the characteristic “stippling” pattern indicative of a turtle on a big boulder.
“We gathered the pieces around it, and we could see places where the bone was visible on the outside, so we decided to collect the whole thing,” Schein said. Along with David Parris, Curator of Natural History, Schein and two other Expedition crew members loaded it onto a blanket and carried it the quarter mile back to the truck, and then on to their laboratory.
More than a year’s worth of meticulous work with tiny air-powered jackhammers in the Paleo Lab at the Academy of Natural Sciences of Drexel University, slowly chipped away the hardened iron carbonate mineral stone, revealing a nearly complete turtle.
“It turned out to be the best fossil we’ve found yet. Fossils are very rarely found complete,” Schein said. “To find such a large percentage of a skeleton, and to find a skeleton that is so perfectly articulated, that it looks like it died yesterday, is very, very rare.”
Also rare is that the turtle “is so clearly demonstrating some kind of behavior,” he said. “When a turtle gets stressed, it tucks in its head and pulls its arms in, and that is what this turtle is doing. That is what happened when he died, when he got buried.
“We do a lot of interpreting of behavior, but it is not often that we see behavior,” Schein continued. “There is something special about seeing that last moment of that animal’s life so long ago.”
The fossil is dated to 65 million to 67 million years ago, around the time that dinosaurs went extinct, Schein said.
“He was living right alongside the last of the T. rex and Triceratops,” he said. The fossil may be “one of the most complete examples of this species anyone has ever seen.”
The turtle will be in a case so museum visitors can walk around and view it from all angles. Eventually the scans from New Bolton Center may be incorporated into the display.
The exhibit also includes a first-ever standing display of a full skeletal replica of the Dryptosaurus, the first carnivorous dinosaur discovered. The original skeleton pieces – found in 1866 in Gloucester County, New Jersey – are at the Academy of Natural Sciences in Philadelphia.
This week Schein, Anné, and Malinowski are on their way to the Bighorn Basin Dinosaur Project’s 2016 Field Expedition.