A study published recently in the journal Quaternary Science Reviews, led by Ruth Blasco, a researcher at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), offers new data on the bone modification patterns of cave bears (Ursus spelaeus) at the Paleolithic site of Cova del Toll, in Moià (Barcelona), which help to interpret their cannibalistic behavior.

The work compares the fossil record of the species U. spelaeus with data from experimental observations of the brown bear (U. arctos) in the Pyrenees and, more specifically, it centers on determining the origin of a bone modification known as peeling, which can be produced by both ursids and humans.

“When ursids consume complete carcasses, they generally use their front paws as though they were hands, pressuring and bending the animal's thoracic cage until some of the ribs and vertebrae break, in an endeavor to access the viscera”, explains Blasco. These fractures, known in the English literature as peeling, are characterized by the fact they leave surface peeling and frayed bone edges similar to those identified in the 1990s in faunal assemblages altered by primates (humans and chimpanzees).

Because a single bone modification may be produced by two different biological agents (humans and bears), this creates a problem for taphonomic interpretation of the fossil record. This is precisely what happens at Cova del Toll Level 4, dated to over 50,000 years old, where bone peeling has been identified on cave bear vertebrae and ribs, together with evidence not just of carnivore activity, but also that generated by hominins in the form of a small collection of stone tools and cut marks on the bone remains themselves.

Earlier work

To deal with this conundrum, the new study gathered the actualistic data found in a work led by Maite Arilla (Universitat Rovira i Virgili) in 2014, which describes the consumption pattern of Pyrenean brown bears for a total of 17 ungulate carcasses, and where peeling was identified as one of the principal modifications in axial bones (vertebrae and ribs).

In addition to this, other data from various studies analyzing the bone alterations produced by groups of chimpanzees in captivity and of modern humans like the Khoikhoi of Namibia were also assembled.

This entire dataset was compared statistically, yielding results that enable the authors to identify cave bears as the main effectors of the peeling found on the bones from Cova del Toll.

“This opens up multiple windows for us to interpret the behavior of cave bears such as, for instance, their tolerance of hibernation with other individuals (in a group), which gives rise to a scenario in which those that woke up could immediately access the cadavers of those that had been unable to survive the process of lethargy”, says Jordi Rosell, of the Universitat Rovira i Virgili (URV) and the Institut Catalá de Paleoecologia Humana i Evolució Social (IPHES).

This study, in which researchers from the Universidad de Alcalá de Henares and the Universidad Complutense de Madrid also participated, is an example of how equifinal processes present at archaeological sites pose challenges to interpreting the authorship of certain bone modifications.