Hyenas Left a Massive Pile of Bones in a Saudi Arabian Lava Tube

Hyenas Left a Massive Pile of Bones in a Saudi Arabian Lava Tube
One of the bone accumulations in the Umm Jirsan lava tube in Saudi Arabia. (Photo: Richard Clark-Wilson)

Scientists investigating a dried-up lava tube in northwestern Saudi Arabia were stunned to find a huge assemblage of bones belonging to horses, asses, and even humans. It was a feast to last a lifetime, and then many lifetimes after that, and the researchers who excavated the site believe they know the identity of the hungry species that amassed the bone bed.

“In a nutshell, we argue striped hyena. Striped hyena are very avid accumulators of bones,” said Mathew Stewart, a zooarchaeologist at the Max Planck Institute for the Study of Human History, in a video call. Though the hyenas are now ecologically threatened in Saudi Arabia, they used to be a mainstay in the lava fields in the country’s northwest and roamed the region for the better part of the Holocene epoch, from which all the bones in the lava tube dated. Stewart and his team’s analysis of the site was published last week in Archaeological and Anthropological Sciences.

Though the nearly mile-long lava tube was discovered in the mid-2000s, earlier researchers didn’t venture too deeply into the cave. (A previous team said they heard growling in the lava tubes, a bone-chilling indication that the threatened hyena population in Saudi Arabia might still have a happy home in remote reaches of the country.) The main goal of the team behind this latest paper was to figure out how the huge number of bones — hundreds of thousands of them, representing at least 40 different species and dating from about 7,000 years ago to the Victorian era — ended up collecting in the lava tube’s rear.

The researchers determined hyenas were the culprits after cataloguing all the bones and examining cut marks, tooth marks, and digestion marks on them, as well as how the bones had fragmented. Stewart said that a telltale sign that striped hyenas were to blame was the several human crania on the site; the scavengers are known for pilfering human graves for meat. “It’s always just the skullcap that survives” with striped hyenas, he said. “They seem to not really be interested in skull caps. We found maybe five or six skullcaps with gnaw marks on them at the site, but only the skullcaps. Nothing else.”

The research was conducted as part of the Palaeodeserts Project, an effort to understand the ancient environment in what is now the Arabian Peninsula and how that environment changed over time. Important to that investigation is an understanding of human and animal movements across the region; due to Saudi Arabia’s harsh conditions, precious little in the way of fauna remains has stuck around long enough for expert analysis. Bones can get so brittle that they disintegrate when handled, which makes the hyenas’ hoard a precious source of knowledge.

The a cavernous opening in the Umm Jirsan lava tube, illuminated by a researcher's light. (Image: THE PALAEODESERTS PROJECT) The a cavernous opening in the Umm Jirsan lava tube, illuminated by a researcher’s light. (Image: THE PALAEODESERTS PROJECT)

“The most surprising thing comes down to just how well preserved the material is, and how much material there is, given that in Saudi we have no faunal remains, really,” Stewart said, adding that when the team typically does have remains to examine, the bones are in such degraded condition that little can be determined from them, leaving the team to use other evidence — even rock art depictions of ancient life in Saudi Arabia — to get a gist for what lived in the area and when.

Now that such a large repository of animal history has been found, the team hopes to pull genetic information from the bones. They also think they can learn about the animals’ diets and migrations based on isotopes lodged in their ancient teeth. Nice work, hyenas.

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