New research reveals that the fossilized bones of "Ushikawa Man," believed to be among Japan's oldest human remains dating back 20,000 years, are not what scientists originally thought.

Rather, they belong to the skeletal remains of a prehistoric bear.

The fossils were found in the late 1950s in the city of Toyohashi, about 140 miles (225 kilometers) southwest of Tokyo. But Gen Suwa, an anthropologist at the University of Tokyo who led the new project, told Live Science that doubts about the Ushikawa fossils were first raised in the late 1980s, and had continued since then.

The new research, published Dec. 1, 2024 in the journal Anthropological Science, shows beyond a doubt that the bones are from an ancient brown bear, Suwa said in an email.

He noted that bear bones were seldom discovered in archaeological sites in Japan from that period, which meant that Japanese researchers—including the paleontologists who unearthed the fossils in the 1950s—had a rather restricted comprehension of the appearance of bear bones. Nevertheless, Suwa mentioned that these researchers had produced "thorough and highly precise" descriptions and had gathered a significant quantity of fossilized skeletal remains over many years.

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Ancient skeletons in Japan

The fossils are referred to as the Ushikawa fossils, named after the Ushikawa area in Toyohashi, where they were discovered in a quarry between 1957 and 1959. According to Suwa, Japanese researchers of that era believed that another bone fragment, called "Akashi Man," represented the oldest human fossil found on the Japanese mainland, estimated to be over 780,000 years old. Unfortunately, this fossil was lost during an Allied air raid over Tokyo in World War II.

In the 1980s, an examination of a plaster cast of the Akashi fossil, which had been lost, suggested that it was likely a piece of a modern human arm bone that had been displaced into a different archaeological layer and subsequently mineralized. This discovery sparked increased interest in the Ushikawa fossils, according to Suwa.

The Ushikawa fossils were initially presented as a humerus bone from the upper arm and the end or head of a femur bone from the leg of a human who had lived more than 20,000 years ago. But in the new study, a visual examination and computed tomography (CT) scan revealed that the supposed human humerus was probably the radius bone from the forearm of a brown bear (Ursus arctos) from about that time, while the head of the femur was also determined to be from a bear, Suwa said.

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Ancient fossils

The discovery that the Ushikawa fossils are not human means the oldest human fossils found on the Japanese mainland are from a limestone quarry near the Japanese city of Hamakita, about 25 miles (40 km) east of Ushikawa.

The remains include pieces of a human femur, humerus, clavicle, and cranium, believed to belong to two distinct individuals—one dating back approximately 14,000 years and the other around 17,000 years.

Human fossil remains have also been found on Japan's Ryukyu Islands — also known as the Nansei Islands — situated about midway between Japan and Taiwan. Scientists think the youngest of these fossils date from about 18,000 years ago, while the oldest may date from up to 32,000 years ago.

The latest finding in Japan is not the first time that human and bear bones have been confused: A bone found in a cave in Alaska in the 1990s was once thought to be from a bear, but new research has shown that it is from a Native American woman who lived about 3,000 years ago.