An extraordinary horde of bones – including human remains – preserved inside a lava tube for thousands of years has been discovered in Saudi Arabia.
The deserts of the Arabian Peninsula are notoriously reluctant to give away their ancient secrets, and offer an exceptionally scant fossil record that continually frustrates paleontologists. This discovery finally illuminates the prehistory of this enigmatic region.
Described in the journal Archaeological and Anthropological Sciences, the grisly collection includes the bones of horses, donkeys, gazelles, camels, and cattle, as well as multiple human skull fragments. Numbering in the hundreds of thousands, the bones appear to have been amassed over a period of 7,000 years. They were discovered inside the Umm Jirsan cave which sits within Saudi Arabia’s Harrat Khaybar lava field.
“The Harrat Khaybar lava tubes represent an untapped resource in a region where bone and fossil preservation is otherwise exceptionally poor,” write the study authors. “Such sites have the potential to inform on the paleoecology and prehistory of this understudied region.”
Previously, researchers studied the rock art record in an attempt to learn about the ancient fauna of these mysterious deserts. This approach has revealed the presence of species like aurochs and asses in the area during Neolithic times, despite the complete absence of these animals from the fossil record.
This latest finding paints a more precise picture of the local prehistoric ecology, revealing that donkeys and cattle have been prevalent in the area for many thousands of years.
Announcing the discovery on Twitter, study author Matthew Stewart wrote that the “1.5 km [0.9-mile] long lava tube is chock-a-block with hundreds of thousands of beautifully preserved animal remains. But why?”
The researchers dedicate most of the paper to answering this question, looking into whether the bone collection may have been assembled by a number of potential culprits including wolves, foxes, leopards, panthers, and even lions.
However, after noting that all of the bones appear to have been extensively “processed” – either by gnawing or partial digestion – the authors decide to rule out all big cat species, since these animals “do not possess the skeletal and muscular apparatus for intensively processing dense skeletal remains.”
Wolves, meanwhile, are not known to carry their prey large distances from the kill site, and foxes simply are not big enough to have transported the remains of horses, camels, and other large creatures.
Striped hyenas, however, are perfectly capable of doing so, and have even been observed carrying entire wildebeest legs over distances of several kilometers.
Furthermore, markings on the bones match up with typical hyena gnawing and digestion processes, while the presence of hyena bones and fossilized hyena droppings provide the final incriminating evidence.
“By studying the types of bone surface modifications, their frequencies, & locations, we conclude that the bones at Umm Jirsan were brought in by striped hyena,” explained Stewart in a subsequent tweet. “These critters are avid collectors of bones, which they transport to dens to be consumed, fed to young, or cached.”
As for the human remains found in the cave, radiocarbon dating revealed these the youngest of these fragments to be around 150 years old, with the oldest being approximately 4,000 years old. According to the study authors, these cranial pieces may have been looted by hyenas from human graves.