Grounded: Fossil of pterosaur actually came from turtle
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BANDO, Ibaraki Prefecture—A fossilized bone piece long hailed as coming from a pterosaur flying reptile is actually from a “suppon” softshell turtle, according to a re-examination that started with a dinner that included the four-legged delicacy.
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The fossil was found in 2002 in a 72-million-year-old stratum from the late Cretaceous Period at Hiraiso Beach in Hitachinaka, Ibaraki Prefecture, and donated to the Ibaraki Nature Museum here.
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When the museum sent a replica to a researcher in Germany for analysis, it was described as a “shoulder blade of a pterosaur.” That made it the first fossil of a prehistoric winged reptile found in the Kanto region.
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Nicknamed “Hitachinakaryu” by locals, the fossil had been featured in sightseeing pamphlets and submitted to exhibitions outside the prefecture.
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But one day in 2017, Ibaraki Nature Museum curator Taichi Kato, 32, took apart a suppon turtle during a hot pot dinner at his home after finishing a scientific paper. He noticed that its upper arm bone was similar in shape to the Hitachinakaryu fossil.
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Kato borrowed a CT scanner from an optical instrument maker and found the fossilized bone had a sponge-like structure inside, which is typical of turtles. Bones of a pterosaur are usually hollow.
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“I realized then and there that it was not of a pterosaur,” Kato recalled.
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The bone appeared hollow from the outside because part of the inner structure apparently drained out through a chip at the top.
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Kato also noted that since 2013, three other fossilized pieces of suppon turtle shells have been found in a spot near the stratum where Hitachinakaryu was found.
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After comparing its shape to that of an upper arm bone of turtles, Kato concluded in spring 2020 that the fossil was from a suppon of the Cretaceous Period.
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When the chipped part is reconstructed, the fossilized right upper arm bone is about 12.5 centimeters long, indicating that the turtle had a large shell up to 70 cm in diameter.
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Although Hitachinaka may have lost its pterosaur claim to fame, the turtle fossil still represents a first.
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Fossils of similar-sized suppon from the Cretaceous Period have been excavated in North America, Kazakhstan and elsewhere.
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But Hitachinaka is the only place in East Asia where such a fossil has been found.
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“With the advancements in analysis methods, it is common to see previous views proven otherwise,” Kato said. “It serves as a lesson not to make the same mistake again, and I have a renewed determination to find a fossilized pterosaur next time.”
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Hitachinaka city officials published the results of the re-examination in the February issue of its newsletter. They are correcting related entries on its website and in official publications.
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The fossil is on display for a special exhibition at the Ibaraki Nature Museum through June 13.
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