The use of tooth pits to identify carnivore taxa in tooth-marked archaeofaunas and their relevance to reconstruct hominid carcass processing behaviours

1. What they did

When archaeologists find old bones with tooth marks, they know carnivores chewed them, but not which carnivores. That matters for understanding how early humans and carnivores shared carcasses. The authors tested whether the size of tooth pits (small round dents left by a tooth pressing into bone) can tell carnivores apart.

They measured the length and breadth of conspicuous tooth marks on bones chewed by six kinds of animals:

• Lions (fleshed bones), northern Maasai Mara National Reserve, Kenya.
• Jackals (fleshed bones of a small carcass), two feeding experiments in Tsavo East, Kenya.
• Bears (fleshed bones), feeding experiments at the Cabarceno natural reserve, Spain.
• Hyenas (defleshed bones), experiments in Galana and Kulalu, Kenya, and a carcass eaten by people and then ravaged by hyenas.
• Baboons (defleshed bones), Barcelona zoo, Spain, and Tsavo East.
• Dogs (defleshed bones), feeding experiments with German shepherds.

The carcasses were medium-sized bovids or equids, apart from the jackals’ small carcass. Marks were measured with magnifying lenses and an electronic calliper on moulds. They split the marks by bone type: spongy (cancellous) bone from the ends of limb bones, and dense (cortical) bone from the middle of the shaft. They focused on pits and measured scores (marks about three times longer than wide) for comparison. They added an earlier study’s data on leopards and cheetahs, then used their results to re-examine claims about carnivores at FLK Zinj, an early hominid site at Olduvai Gorge, Tanzania.

2. What they found

Pits and scores

• In pits from every carnivore, length and breadth rose together, on both spongy and dense bone. Tooth size is the main reason.
• In scores this link was not regular, because scores are made by dragging tooth cusps and do not depend on tooth size alone. So pits are more useful than scores for identifying carnivores.
• Pits and scores were bigger on spongy bone than on dense bone.

Pit length on spongy bone (bone ends) gave three groups

• Under 4 mm: moderately conspicuous marks, seen in all carnivores except lions. Samples with most marks this small come from jackals and middle-sized cats (leopards and cheetahs). Larger dogs seem to leave bigger marks than middle-sized cats, because dogs tend to gnaw bones while cats try to avoid it.
• 4 to 6 mm: mostly middle-sized and large carnivores, but not cats other than lions. On average these belong to baboons, dogs and bears.
• Over 6 mm: large carnivores, on average lions and hyenas.

Pit breadth gave a similar picture: under 2 mm for middle-sized cats, 2 to 4 mm where most carnivores overlap, and over 4 mm for hyenas, bears, lions and dogs.

Dense bone (mid-shaft)

• Only two broad groups: marks under 2 mm long and 1.5 mm broad from small carnivores such as jackals and from middle-sized cats, and larger marks from the rest.
• Differences were only clear for marks over 4 mm long and 2 mm broad, which could come from hyenas, dogs or lions.
• On dense bone, carnivores converge so much that it is almost impossible to pick out one species from pit size alone.

Mean pit sizes (Table 1, spongy bone)

• Hyenas 7.37 mm long (50 marks), lions 6.5 mm (13), bears 5.24 mm (44), dogs 4.93 mm (23), baboons 4.6 mm (34), jackals 3.5 mm (40).

Length to breadth ratios and FLK Zinj

• The length to breadth ratio of pits was similar for every carnivore (means 1.45 to 1.83). Lumping all carnivores together gave a ratio (1.55) and spread (0.47) similar to single carnivores.
• So a wide spread of ratios at FLK Zinj, used by Selvaggio and Wilder (2001) as evidence that several carnivores chewed the bones, need not mean several carnivores. The authors also found that the FLK Zinj sample mixed pits and scores.
• The FLK Zinj pit sizes were mostly similar to those of spotted hyenas.

3. What they concluded

• Tooth marks alone cannot confidently identify a particular carnivore species. Tooth mark size can separate groups of carnivores, and small carnivores and middle-sized cats can clearly be told apart from larger carnivores on both kinds of bone.
• Single marks are of little use. Pit sizes are only helpful as a large sample, looking at their spread and range of variation, together with other clues: where the marks are on each bone and element, and how much bone is furrowed (gnawed away). For example, intense furrowing of the ends of most limb bones is more likely the work of hyenas and dogs than lions, which furrow mainly the ends of the upper limb bones (humerus and femur).
• Even so, a specific carnivore can only be confidently named when comparing small with large carnivores.
• Tooth pit size cannot support the three-stage model (carnivore, then hominid, then carnivore) proposed for FLK Zinj. Medium-sized cats such as leopards and cheetahs mostly hunt animals smaller than 150 kg, so they are unlikely to have defleshed the mostly middle-sized carcasses there.
• Experiments have not yet ruled out equifinality (different causes leaving the same traces), and more research is needed.

4. How tracking was or was not used

No tracks or trailing were used. The study is about reading one kind of sign: tooth marks left on bones by feeding carnivores. The authors measured these marks on bones from known carnivores to see whether the marks can identify which animal did the chewing.

6. Other technologies, skills or innovations

• Moulds of tooth marks made with a dental-type moulding gel (Ventura Top light and catalyst, similar to Xantopren), measured with binocular magnifying lenses and an electronic calliper.