In anthropology and archaeology, a bulbar depression is a diagnostic feature of stone tool production, referring to the concavity left on a core after a flake has been struck off. It is closely associated with the bulb of percussion and helps specialists identify intentional knapping versus natural breakage.
🌍 Definition
- Bulbar Depression: A distinctive mark left on the core beneath the striking platform after a flake detachment.
- Formation:
- When a hammerstone or percussor strikes the core, energy propagates through the stone.
- The flake detaches, leaving a swelling (bulb of percussion) on the flake and a corresponding depression on the core.
- Diagnostic Value: Confirms human agency in lithic reduction sequences.
🔑 Archaeological Contexts
- Lithic Analysis:
- Bulbar depressions are studied alongside bulbs of percussion, striking platforms, and ripple marks.
- Their presence indicates controlled flake removal rather than accidental fracture.
- Technological Insight:
- The size and shape of the depression vary depending on raw material, angle of impact, and force applied.
- Hard hammer percussion tends to leave more pronounced depressions, while soft hammer percussion produces subtler ones.
- Experimental Archaeology:
- Replicative knapping experiments help archaeologists understand how bulbar depressions form and what they reveal about toolmaking skill.
📚 Importance in Anthropology
- Human Behavior: Evidence of intentional tool production and mastery of fracture mechanics.
- Cultural Identity: Different lithic traditions can be distinguished by percussion features.
- Comparative Value: Natural fractures rarely produce bulbar depressions, making them diagnostic of human knapping.
- Material Culture Link: Connects geology (fracture mechanics of flint, chert, obsidian) with human technological skill.
In short: A bulbar depression is the concavity left on a core after flake removal, serving as a key marker of intentional human knapping in lithic analysis.
Sources: Glossariz – Bulbar Depression Definition; Cambridge University Press – Stone Tools in the Paleolithic and Neolithic Near East; BAJR Practical Guide to Lithics.
