Leopards as taphonomic agents

Taphonomy is the study of bones from the time the animal dies to the time the bone is recovered for study.Several agents are responsible for modifying and accumulating bones and leopards (Panthera pardus) are one of them. Initially several schools of thought were of the idea that leopards took their prey onto trees to protect it from competitors but we now know that they use deep recesses of caves whenever available.The following case studies serve to illustrate the importance of leopards as taphonomic agents.

Mount Suswa Caves

Studies of modern bone assemblages reveal that a number of potentially identifiable processes may have led to fossil bone accumulations.The behaviour of leopards has been documented in many areas of Africa. Coryndon (1964) did a study of bone remains in Mount Suswa lava caves in Kenya and came to a conclusion that a number of collecting agents had been at work, including leopards (Panthera pardus Linnaeus), hyaenas, owls and men. He wrote, “Predatory animals prefer certain definite conditions in which to take their food – thus the leopard seems to prefer a very dark recess where no light can penetrate”. One such cave had a floor strewn with the remains of many baboons and a few small antelopes, presumably brought in by leopards.

A more specific study of leopard involvement in the bone accumulations of the Mount Suswa caves was done by J.W. Simons (1966), who studied both the skeletal remains of the leopards themselves and those of their prey, the baboons (Papio cynocephalus Linnaeus) that were using the caves as their sleeping site. Baboon remains had tooth holes and the skulls, some with associated mandibles, showed characteristics which Simons attributed to the chewing habits of leopards. Simons wrote, 'Particularly all the baboon remains show extensive carnivore damage, including numerous punctuate marks, presumably caused by the leopard canines'. No less than 37 individual baboons were found to occur in the caves, of these, the deaths of four were attributed to falling over the edge of a shaft, probably induced by attacking leopards. The remainder were killed and dragged into the caves to be eaten, probably by leopards. Also some of the leopard remains showed signs that these leopards might have fallen to their deaths over the edges of a shaft, probably chasing after the baboons.

Swartkrans

Bone fragments obtained from Swartkrans, South Africa during the 1948-52 palaeontological work at the site were analysed by C.K. Brain (1969). He came up with a conclusion that the kind of damage found to be present on the fossil skeletons suggests it was influenced by carnivores with bone crunching ability intermediate between that of spotted hyenas on the one hand and cheetahs or sabre-tooths on the other . According to C. K. Brain (1969), a carnivore that shows this kind of ability is the leopard, remains of several of which have already been found among the Swartkrans fossils . Comparative studies on leopard food remains in various areas have shown that the damage done to skeletons is influenced by the availability of food at the time and the competition which the leopards experience from hyenas. The Swartkrans bone accumulation shows many characteristics of food remains left by leopards which were feeding under a fair amount of competitive pressure .

Various lines of evidence have suggested that leopards were the predators responsible for killing the Swartkrans Australopithecines. One of the direct pieces of evidence is in the form of damage to a Paranthropus skull . SK54 is part of the fossilised skull of a Paranthropus child, showing, in the occipital region, two round holes. The spacing and diameter of the holes is such that they could well have been made by the lower canines of a leopard while, in fact, the canines in the mandible of a fossil leopard from the same part of the deposit fit the holes remarkably well . In his paper, Brain, (1969) concludes that various lines of reasoning point to the suggestion that, leopards were one of the most important agents responsible for collecting bones at Swartkrans .

In 1981, C. K. Brain in his publication “The Hunters or the Hunted”, concurred that, leopards are secretive predators that make use of caves as retreats, feeding places and breeding lairs. In addition they have the habit of storing food in trees, which in the case of Sterkfontein valley caves, may have had special local significance from the taphonomic point of view . The tree stashing behaviour of leopards has been used as a model to account for the deposition of bones in some of the fossil caves of South Africa.

Verloren Farm, Namibia

Brain (1981), from his extensive research on the Quartzberg leopard feeding lair in Verloren Farm in Namibia made the following observations. Of the 211 bone species collected, 147 regarded as porcupine collected and 64 as probably leopard collected.

Dassie fossil remains showed that the brain case and posterior part of the mandible had been sheared off, leaving ragged, tooth marked edges. This damage to the bones was then confirmed by experiments with leopards and dassies in Valencia Farm (Namibia) by Brain in 1968. The damage to the skull was found to be remarkably similar to that observed in dassie crania from the natural leopard feeding lairs. The brain case had been chewed away, and a punctuate mark was present below the right orbit. All of the right and most of the left ascending mandibular rami had been chewed away, leaving typical ragged edges.

© Image: C.K. Brain
Characteristically damaged skulls of dassies found in three leopard feeding lairs: (a)Quartzberg cave; (b) Valencia lair; (c) Suswa leopard lair, Kenya.

In Southern Africa in particular, examinations of modern bone assemblages indicate that in cave situations, carnivores, particularly leopards and hyaenas and rodents such as porcupines, are the most significant non-human accumulators of large bone assemblages.

John Nash Nature Reserve

The discovery and examination by de Ruiter & Berger (2000) of a modern leopard lair in a dolomitic cave on the John Nash Nature Reserve, near Johannesburg, South Africa provided an alternate model for the deposition of fossils in dolomitic caves in South Africa. The bone accumulation formed in this cave was the consequence of a leopard dragging complete carcasses into the cave itself and the resultant bone assemblage reflects the behavioural patterning of that leopard . This is in contrast to the model of leopards consuming prey in the trees growing in cave entrances, and randomly dropping bones into the cave from those trees. This is evidenced by almost to completely articulated remains found in the lair (WU/BA-001) compared to disarticulated remains that would have resulted from the bones dropping off a tree in a cave's entrance.

De Ruiter & Berger (2000) divided the leopard lair WU/BA-001 in the John Nash Nature Reserve into three zones, namely the light zone (entrance), twilight zone (about 3m from entrance, then dark zone (remainder of lower chamber).They observed that there were no bones in the light zone, few in the twilight zone and more in the dark zone with some remains displaying carnivore damage. They wrote "Instead, there is good deal of evidence that a leopard was the sole accumulating agent based on relatively complete skeletons or at least articulated remains". The eland (Taurotragus oryx) found in the dark zone of WU/BA-001 showed tooth panctures along it's neck, consistent with having been dragged, as well as removal of it's internal organs, a characteristic leopard behaviour.

Adult female eland (Taurotragus oryx) in leopard lair WU/BA-001 IN 1991.

Also most of the carcasses in the lair had been chewed by a large carnivore in a manner suggestive of leopard feeding. Based on WU/BA-001 de Ruiter & Berger (2000) then came to the following conclusion, “in the presence of dolomitic caves, leopards will preferentially use the deep recesses of the cave itself, rather than overhanging trees, for the storage and private consumption of kills”. This conclusion agrees with Brain’s (1993) revised model for the deposition of hominid bones in the caves of the Sterkfontein valley. They (de Ruiter & Berger , 2000) concure that all of the carcasses attributed to the leopard in WU/BA-001 were deposited within the cave itself, and non could be ascribed to a kill which had been dragged into a tree, despite the fact that there are several large trees (Olea capensis) growing in the entrance of this cave.

Several wild Olive trees (Olea capensis) growing in the entrance area of WU/BA-001. No bones were located in the catchment area underneath these trees.

Pickering et al. (2004) dispute de Ruiter & Berger's conclusion that leopards were responsible for the accumulation of all WU/BA-001 bones regardless of prey body size. This was in reference to the remains of eland (Taurotragus oryx) which has an average live weight of 350-450kg as well as Zebra (Equus burchelli) observed in another close-by leopard den WU/BA-002

Adult Burchell's zebra skeleton located in leopard lair WU/BA-002.

Pickering et al, (2004), did measurements on tooth pits on bone specimens from Swartkrans Member 3. The results obtained pointed to the fact that tooth pit dimensions from small animals show a restricted range of variation and overlap with dimensions observed in modern tooth pit samples created by carnivores with less robust teeth, comparing most favourably to the leopard- derived sample. In contrast, tooth pit dimensions on Swartkrans specimens from large animals compare very closely to those created by modern large dogs, spotted hyaenas and lions. This clearly indicates that large carcasses recovered from Swartkrans Member 3 were likely modified predominantly by carnivores other than leopards. They observed a relatively abundant occurrence of stone tool cut marks and hammerstone percussion damage on bone specimens across all animal body sizes, indicating that hominids exploited a wide range of carcass types.

Conclusions

In conclusion, Pickering et al, (2004) wrote, “In addition, our results highlight the hazards of blanket statements based on the application of inadequate actualistic criteria in complicated taphonomic settings, such as that at Swartkrans”. They go on to say that the indirect evidence of modern leopard killing and carcass transport capabilities is by itself not sufficient to explain the deposition of variably sized animals during the Plio-Pleistocene in South African cave site. However, the fact that Pickering et al, (2004) did not dare visit the leopard lairs in question (WU/BA-001 & WU/BA-002) to see the leopard signatures left on the accumulation in these caves it means they can not fully dispute de Ruiter and Berger's conclusion that the leopard was responsible for the deposition of large sized animals in these lairs. In summary, leopards are potentially a significant accumulator of bones in caves and they can take up prey larger than their own body size since movement in the caves is aided by gravity unlike on trees where the force of gravity would impede carrying of large bodied prey. Leopard accumulations may indicate the opportunistic behaviour of leopards in general, as well as the differences in local environments and fauna. Assemblages may reflect, not so much the collecting agent, but perhaps the prevailing local conditions in terms of environment and animal community. It must also be concluded that leopards use trees to stash their prey so as to protect it from competitors like hyaenas but in the presence of dolomitic caves, they prefer the dark recesses of these caves to protect their prey.