Experiments suggest rockfall an improbable cause for bone surface modification on 24,000-year-old bone at Bluefish Caves, Canada

Abstract

At Bluefish Caves in the Yukon Territory of Canada, researchers argue that 24,000-year-old faunal remains bear anthropogenic cutmarks, and provide evidence of a pre-Last Glacial Maximum (23-18 ka) human occupation of North America's arctic. However, non-anthropogenic agents can also leave marks on bones that might resemble bone surface modifications (BSMs) produced by stone tools. Here we test the hypothesis that rockfall traces can mimic stone tool cutmarks by experimentally replicating the spalling limestone shelter at Bluefish Caves, dropping variably sized limestone blocks (12–2322 g) from 3.5 m onto Bovidae remains. These same bones were subsequently sliced with stone tools to produce cutmarks for comparison. The resulting marks were analyzed with a Dino-Lite microscope and a Sensofar S Neox 3-D optical profilometer to allow quantitative comparisons of their morphologies. Results show that cutmarks can be distinguished from rockfall damage, and do not support the hypothesis that the BSM previously identified as cutmarks at Bluefish Caves are instead a product of rockfall.