Maebashi, Gunma Pref. – Fossils unearthed in Gunma Prefecture dating back about 15.5 million years have been identified as a new species of sperm whale, offering clues on the evolution of the deep-diving marine mammals. The species, named Miophyseter gunmaensis, combines traits of ancient and modern sperm whales. It is the third new sperm whale species identified from fossils in Japan, following discoveries in Nagano and Aichi prefectures.
The fossils will be on display at the Gunma Museum of Natural History in the city of Tomioka through Dec. 13. Representing three individuals, they were discovered by local fossil enthusiasts between 1994 and 2011 along tributaries of the Tone River that flow through Tomioka and the city of Annaka, both in Gunma Prefecture. One specimen includes nearly a complete skeleton, and is believed to be that of a calf measuring 3 to 4 meters long.
Modern sperm whales dive into the deep sea and suck in their prey, while their ancestors hunted in shallower waters and bit their targets, according to Toshiyuki Kimura, a curator at the museum. The newly identified species had a large depression in its skull, thought to have helped it withstand the pressure of deep water, as well as well-developed throat bones that enabled it to suck in prey. But it also had more teeth than modern sperm whales, suggesting it used both suction and biting to feed.
The study was published online in August in the U.S.-based Journal of Vertebrate Paleontology.
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