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Ungulates Gnawing: Osteophagia & Bone Modifications

24 Oct

Osteophagia: Osteophagia is the act of ungulates (including giraffes, camels, cattle, etc.) chewing on another species skeletal remains to gain nutrition (particularly minerals such as phosphorus and calcium) that may be lacking in other parts of their largely vegetarian diets.  This includes the chewing of antlers, horns and ivory, as well as skeletal elements.  It is a relatively well documented animal behaviour that occurs across numerous taxa and across continents.

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I’ve been meaning to highlight this article by Hutson et al. (2013) for a while as it nicely illustrates the actions of animals in the archaeological record that can sometimes be interpreted, or mistaken, for a human or taphonomic origin.  Hutson et al. (2013) discusses the impact that ostephagia can have on archaeological contexts and carefully identifies the differences between large and small ungulate osteophagia-based actions.  Taking 12 individual and observed case studies of osteophagia examples recovered from modern field contexts in Australia, North America and Africa, the study highlights the different styles of bone modifications made by each species to help identify the often distinct bone modifications that they leave in their wake.  The case studies include examples of wildebeest (C. taurinus) bones having been gnawed by giraffes, elephant (Loxodonta africana) ivory gnawed by kudu or sable antelope, and a camel (C. dromedarius) radius fragment having been gnawed by a camel.

Hutson et al. (2013: 4140) notes that ‘previous studies have shown that ungulates gnaw both cortical and cancellous bone and elements in almost any state, from fresh to completely bleached, desiccated, and weathered”.  The favoured bones to gnaw during scavenging among ungulates are elements of the long bones, vertebrae, scapulae, skulls and ribs, and, if munching on long bones, the larger ungulates often position the axis of the bone ‘like a cigar held in a human mouth’ (Hutson 2013: 4140).

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This diagram shows porcupine gnawed B. taurus limb elements, where a) is the right tibia and b) is the left femur. Notice the what look like long striations, which are in fact gnawing lines (click to enlarge). Image credit: Fig 8 from Hutson et al. 2013: 4147.

Importantly, the authors differentiate the classes of ostephagia-based bone damage caused by large ungulates and compare it to the typical bone damage caused by carnivores and other primarily meat-eating scavengers, such as lions, panthers and tigers.  This comparative approach takes into account 10 separate features of bone damage often found on gnawed skeletal remains (including evidence of prey selection, bone selection, bone state, bone transport, tooth mark type and general morphology amongst others) and highlights the varied differences between the two behaviours of ungulates and carnivores (Hutson et al. 2013: 4148).  Perhaps of primary importance in this article is that fact that tooth morphology varies according to species and purpose, as such the authors explicitly highlight that, alongside this, the age of the individual animal, and thus the state of its teeth, gnawing the bone can affect the patterning expected (Hutson et al. 2013: 4147).

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This rib was found at the fringe of a scatter of skeletal elements from one individual. Showing the distinctive forking and crushing of ungulate gnawing, this B. taurus rib was likely gnawed by cattle whilst still relatively fresh. Image credit: Fig 6. in Hutson et al. 2013: 4145.

Of course care should always be taken in the recording of gnawing evidence, as teeth in both humans and non-humans can wear down and gouging styles can vary.  However, the distinguishing marks made between ungulates during the act of osteophagia and the selectivity of active carnivores and scavengers is vital for the archaeologist as it can infer on the context of the gnawed skeletal remains.  This can help identify the fauna previously present on-site and the actions that took place based on replicating the known evidence.  The analysis of faunal bones at archaeological and palaeoanthropological sites should, of course, be used in conjunction with other taphonomy techniques to fully understand site formation.

All in all, this is an interesting paper that adds real depth to the taphonomic literature and should be of note to both archaeologists and palaeoanthropologists in interpreting the actions of both humans and non-humans during site formation.

Update 26/10/14

Osteophagia is just one method that mammals use to gain extra nutrients in their diet, another method is mineral lick.  As with osteophagia it has long been noted that animals will exploit their environments by eating or otherwise digesting natural soils, clays and rocks to gain elements (particularly salt) that may be missing in nutrient poor ecosystems (Lundquist & Varnedoe Jr 2006).  Mineral lick is particularly prevalent among giraffes, elephants, moose, cattle and tapirs (and other mammals) as a way to increase the amounts of minerals, such as potassium, calcium, sulfur, phosphorus, and sodium, in their diets.  Although the knowledge of so-called salt caves and their origin with animal behaviour is well know, it is thought that they are under-estimated in current estimates of their prevalence (Lundquist & Varnedoe Jr 2006: 18).  As such these natural landscape features should also be taken into account when understanding the formation and duration of palaeoanthropological and archaeological sites.

Bibliography

Hutson, J. M., Burke, C. C. & Haynes, G. 2013. Osteophagia and Bone Modifications by Giraffe and Other Large Ungulates. Journal of Archaeological Science. 40 (12): 4139-4149.

Lundquist, C. A. & Varnedoe Jr, W. W. 2006. Salt Ingestion Caves. International Journal of Speleology. 35 (1): 13-18. (Open Access).