Hyaenas as taphonomic agents

Historical Review

Dart [1][2][3][4] initially interpreted the fossil remains at an australopithecine site at Makapan as bone fragments that were collected and used by australopithecines. This was later to become known as the “osteodontokeratic culture”, due to the hypothesised use of tooth, bone and horn fragments, by australopithecines as tools and weapons. Dart supported his hypothesis by saying that:

• hyaenas are not bone collectors;
• certain skeletal elements were more abundant, indicating selection by australopithecines;
• the biased faunal representation was an indicator of hominid hunting preferences; and
• some of the breakage patterns observed, such as spiral fractures, could only be produced by australopithecines.

Brain [5] found bone fragments similar to those of Makapan, at Swartkrans and attributed their accumulation to hyaena activity.

Which hyaenas are involved?

The family Hyaenidae is made up of four extant species; the striped hyaena (Hyaena hyaena), brown hyaena (Parahyaena brunnea), spotted hyaena (Crocuta crocuta) and the aardwolf (Proteles cristatus). The aardwolf is specialised to a diet of ants and termites, so will not be mentioned again.

The three remaining species, as well as extinct species were all originally thought to fill the same ecological niche, sharing behaviour and feeding habits [6][7]. This was shown[8] to not be the case. Spotted hyaenas are now known to be active hunters, preying mostly on medium to large-sized ungulates [10]. Spotted hyaenas predominantly feed on fresh meat, seldom taking carcasses back to dens, unless to avoid interference competition [10].

Hyaenas as modifiers of bone

In 1980, Brain [11] categorised damage to bones by hyaenas into two types; premolar cracking of small, more manageable bones, and incisor/ canine gnawing on larger, uncrackable bones.

Maguire et al. [12] independently compiled a list of the several types of marks and modifications to bone that hyaenas are capable of. These types of damage are however not unique to hyaenas, but all nine types have been found in accumulations of the three species of bone accumulators, but in differing proportions:

1. Ragged-edge chewing: corresponding to Brain’s [11] incisor/ canine gnawing, but broadened to include smaller bones as well.
2. Shallow pitting: thought that this type of damage was caused by the teeth of juveniles, but not known in 1980 if this was the exclusive cause.
3. Punctate depressions or perforations: caused by the premolars of adult hyaenas. Sometimes a puncture mark is only found on a single surface of a bone.
4. Lunate or cresent-shaped fracture scars: also produced by the premolars, when the bite strength is sufficient to split the bone, so that the fracture line passes through the perforation.
5. Striations or gauge marks: usually short, straight and roughly perpendicular to the to the long axis of the bone. [13] suggested that these striations may be caused by juvenile animals.
6. Continuous or close, irregular and randomly-orientated grooves: appear to be the result of more persistent gnawing, than in the case of striations, and are most commonly found on the ends of long limb bones. Theses grooves also tend to be longer and confined to a smaller region of the bone than striations.
7. Scooping or hollowing out: cancellous bone is removed from the ends of long bones by the incisors.
8. Acid-etching and erosion: caused by bones being swallowed and exposed to gastric acids. Found only in regurgitated and fragments that have passed right through the alimentary canal, and been passed.
9. Splintering or shatter-cracking (comminuted fractures): usually encountered as jagged transverse breaks across the shafts of limb bones.

References

[1] DART, R.A. (1949) The predatory implemental technique of Australopithecus. American Journal of Physical Anthropology. 7: 1-38. [2] DART, R.A. (1955) The cultural status of the South African man-apes. Annual Report of the Smithsonian Institute. 4240: 317-338. [3] DART, R.A. (1957) The osteodontokeratic culture of Australopithecus Prometheus. Memoirs of the Transvaal Museum. 10: 1-105. [4] DART, R.A. (1959) Adventures with the Missing Link. Institutes press, Philadelphia. [5] BRAIN, C.K. (1970) New finds at Swartkrans australopithecine site. Nature. 225: 1112-1119. [6] HUGHES, A.R. (1958) Some ancient and recent observations on hyaenas. Koedoe. 1: 1-10. [7] HUGHES, A.R. (1961) Further notes on the habits of hyaenas and bone-gathering by porcupines. News bulletin, Zoological Society of Southern Africa. 3: 1-2. [11] BRAIN, C.K. (1980) Sterkfontein Valley Australopithecines: The hunters or the hunted? An introduction to African cave Taphonomy. Chicago University Press. [12] MAGUIRE, J.M, PEMBERTON, D., & COLLETT, M.H. (1980) The Makapansgat Limeworks Grey Breccia: Hominids, hyaenas, hystricids or hillwash? Palaeontologia Africana. 23: 75-98.