Porcupine behavior key to fossil formation in Asian karst caves

NANNING, July 28 (Xinhua) -- A multinational research team comprising Chinese, French, and Dutch scholars has demonstrated that porcupine behavior constitutes a crucial factor in the formation and accumulation of cave fossils in karst caves of southern China and mainland Southeast Asia through a combination of fossil observation and zoological experiments.

This study establishes a regional diagnostic framework for identifying porcupine-induced bone modifications in Asia, thereby resolving a long-standing puzzle about how cave fossils formed, a question that has perplexed the academic community for decades.

The findings have recently been published in the Journal of Archaeological Science: Reports.

The Quaternary vertebrate fossils preserved in karst caves across vast areas of southern China and mainland Southeast Asia, including those of apes and hominins, provide invaluable scientific evidence for exploring early human origins, migrations, and dispersals in East and Southeast Asia.

How did these fossils enter the caves? Why are complete skeletons exceedingly rare, with assemblages dominated by isolated teeth, and why do a large number of dental fossils exhibit deficient roots? This question has long perplexed the academic community.

In recent years, researchers have scrutinized numerous animal bite marks on fossil surfaces, narrowing the focus to rodents, specifically porcupines. As the most common members of the mammalian fauna in southern China and mainland Southeast Asia, porcupines have been widely distributed and abundant in this region since the Pleistocene.

Preferring cave dwellings, porcupines habitually transport various foodstuffs, including plant fruits and animal carcasses, into caves for consumption or preservation.

According to Yao Yanyan, associate research fellow at the Anthropology Museum of Guangxi and the first author of the paper, the research team fed fresh animal bones to porcupines and observed how they collected, dragged, and gnawed on them. They then gathered the gnawed bones and scattered teeth left behind. When they compared these experimental samples with fossils unearthed from caves, they found that the gnaw marks, missing tooth roots, and ring-shaped bone fragments on the fossils matched the marks left by porcupines almost perfectly.

During the experiment, the porcupines showed a strong urge to collect bones. Several of them worked together to drag a five-kilogram cow skull, and they kept gnawing at it until only the hard teeth fell out and scattered on the ground, Yao added.

"This explains why dental fossils of various-sized mammals, including Asian elephants, wild boars, sambar deer and macaques are found in these caves," Yao said, adding that tens of thousands or even millions of years ago, porcupines, acting as secondary consumers, retrieved faunal remains left behind by carnivores and transported them back to caves for gnawing to extract nutrients. The harder components of the carcasses, such as teeth, were subsequently discarded and gradually buried.

"Porcupines played a pivotal role in the formation of cave faunal assemblages," said Wang Wei, a professor at Shandong University and the corresponding author of the paper.

Wang noted that this research not only aids paleontologists in understanding the formation of karst cave fossils in southern East Asia and Southeast Asia, but also assists archaeologists in determining whether early hominins played a role in the accumulation of cave deposits.