Carnivore tooth marks and stone tool butchery marks on scavenged bones: archaeological implications

1. What they did

Did early hominids (early human relatives) of the Plio-Pleistocene get meat by hunting, or by scavenging what carnivores left behind? Archaeologists try to answer this from the marks on fossil bones: carnivore tooth marks, cut marks from stone tools, and percussion marks where a hammerstone broke a bone open for marrow. Earlier experiments had people butcher bones first and let carnivores chew them afterwards. This study modelled the reverse: carnivores eat first, and a scavenger with stone tools comes later.

• Watching carnivores eat. Over 7 months in 1989 to 1990, in Serengeti National Park and the Ngorongoro Conservation Area, Tanzania, the author watched free-ranging lions, leopards, cheetahs, spotted hyenas and jackals eat carcasses, from a four-wheel-drive vehicle placed to see well with little disturbance. Every limb in the sample was seen being eaten by carnivores; the hunt itself was seen for 19 of the carcasses.
• Collecting the bones. Once the carnivores had left (and were about 0.5 km away), she collected the long bones that still held marrow and sometimes scraps of flesh.
• Butchering them with stone. Using basalt and quartzite, stones common at early archaeological sites, she (and, for about half the experiments, a Tanzanian butcher who did not know their purpose) cut the limbs apart, removed leftover flesh, skin and tendons, and broke the bones with a hammerstone to reach the marrow.
• Counting the marks. The cleaned bones were examined under a 16 power hand lens in strong, low-angle light, using published criteria to tell tooth marks from butchery marks. Only pieces 2 cm or longer were counted.
• Comparing feeding groups. The 32 carcasses were split by how many carnivores had fed: solitary animals (15 carcasses), small groups of two to four (13), and large groups of nine or 11 (4).

2. What they found

Carnivores at the carcass

• Solitary feeders had no competition and often left limbs barely pulled apart, with skin, tendons and flesh scraps still on them.
• Small groups, often closely related animals such as mothers with offspring or members of one lion pride, showed only moderate aggression and also left flesh scraps.
• Every large group was a mix of at least two kinds of carnivore (cats, spotted hyenas and/or jackals). Competition was most intense here: limbs were pulled apart and the bone ends were often heavily damaged or gnawed away. Marrow was usually the only food left.
• Large-group carcasses were rare to scavenge during the study (only 4).

Marks on the bones (Table 2)

• Across all 584 pieces, more carried tooth marks (65% on average) than percussion marks (46%) or cut marks (34%).
• Bone ends (epiphyses) were the most often tooth-marked (75%) and cut-marked (37%), as they are where muscles attach and joints are cut apart. Midshafts were the least often marked by teeth (47%) or tools (17%).
• On the 35 bones left whole (not broken for marrow), cut marks (67%) were more common than tooth marks (49%), because these came from solitary and small-group carcasses where people still had to cut the limbs apart and remove flesh.
• Standard deviations were large, showing great variation between carcasses.

Ratios that reflect the number of carnivores

• Cut marks to tooth marks: ratios of 2:1 or higher came only from bones left by solitary animals and small groups; the highest ratios came only from solitary feeders. Bones left by large groups had the lowest ratios (half at 0:1, half at 1:1).
• Percussion marks to cut marks: 75% of large-group assemblages had 5:1 or more, while every solitary and small-group assemblage was below 5:1.

3. What they concluded

• How many carnivores fed on a carcass, and how fiercely they competed, decides whether flesh scraps or only marrow are left for a scavenger. This leaves predictable, recognisable marks on the bones.
• Where fossil bones are well preserved, the balance of tooth marks, cut marks and percussion marks could be used to estimate how many carnivores fed first, and so whether a hominid scavenger got flesh or mainly marrow.
• If hominids had come first and carnivores later, cut-to-tooth ratios should be higher than in this study, and percussion-to-cut ratios should stay in the lowest categories.
• Midshaft pieces are best for this, because carnivores scavenging later tend to ignore marrow-emptied midshaft fragments.
• At FLK Zinjanthropus (Olduvai Gorge), the same bones have been used to argue both that hominids came first and that carnivores did. The author argues that both views overlook the range of carnivore feeding behaviour, and that observations of living carnivores plus experiments can help settle the question.

4. How tracking was or was not used

No tracks or trailing were used. The study links directly observed carnivore feeding to one kind of sign: tooth marks on bones, read alongside cut and percussion marks. The author identified the marks herself using published criteria and a hand lens. Seven pieces from young animals, whose bone surface made marks hard to identify, were left out.

6. Other technologies, skills or innovations

• Experimental butchery with basalt and quartzite stone tools and hammerstones, with a standard routine: no scraping of the bone, first blow near the top end of each bone, then blows along the length until the marrow showed.
• A 16 power hand lens under strong, low-angle light for identifying marks.
• Comparing ratios of mark types rather than counts alone, to control for the extra marks created when bones are smashed.