Fossil found in Iwate confirmed to be ancient shark ancestor
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Researchers have discovered a fossil that shares characteristics of an ancient ancestor to sharks, the first such finding in Japan.
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A fossil of the blade-like part of the hybodus species was found in Kuji, Iwate Prefecture, according to the announcement by the Kuji Amber Museum on July 16.
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The hybodus was an ancestor of sharks that lived between the Carboniferous Period of the Paleozoic Era to the Cretaceous Period of the Mesozoic Era, about 90 million years ago.
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A characteristic of the hybodus is a blade-like protrusion in front of its two dorsal fins. The blade is believed to have been a defensive mechanism to keep predators at bay.
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“While there have been findings abroad of the blade, one has never been found in Japan, so this is a significant find,” said Shinya Miyata, a curator at the Oishi Fossils Gallery of the Mizuta Memorial Museum, affiliated with Josai University in Tokyo.
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“Ninety million years ago, the area where the fossil was found was likely near a river mouth, and the fossil is the first evidence that the hybodus existed in such an environment in East Asia.”
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The fossil was found about 300 meters from the Amber Museum in May 2019 by a family visiting the facility. The fossil is about 20 centimeters in length.
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Miyata and Ren Hirayama, a professor of paleontology at Tokyo’s Waseda University, conducted a careful analysis of the fossil and confirmed it is the blade-like part of the hybodus, based on its shallow arc, the lines found on the side and the small projection at the tip.
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Based on the length of the blade, the researchers concluded the hybodus was a small animal, measuring about one meter in length.
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Some modern shark species, like the Japanese bullhead, also have small blade-like parts on its dorsal fin.
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After the fossil’s discovery last year, other fossils found in the general vicinity were examined a second time. That led to confirming that three teeth believed to be from a hybodus were also found nearby.
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Miyata, a specialist in fish fossils, said the hybodus was the only shark species in the Mesozoic Era that had a prominent blade.
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