Palaeont. afr., 23, 105-108 (1980) FAUNAL REMAINS FROM HOT POT CAVE, BREDASDORP by C.E. Gow Bernard Price Institute for Palaeontological Research, Universiry of the Witwatersrand,Johannesburg. ABSTRACT Recent unconsolidated cave deposits can be useful in providing an understanding of how consolidated fossil cave deposits were formed and are far easier and quicker to analyse. This preliminary study describes an extensive, extremely rich bone accumulation in a horizontal cave system linked to the surface by a single vertica I shaft from the middle of a domed chamber. The cave is in Tertiary marine limestone on the southwestern Cape coast. The fauna has two chief components: a macrofauna resulting from entirely fortuitous intro­ ductions such as animals falling down the shaft; and an extensive microfauna accumulated by the barn owl, Tyto alba. Between these two groups there is a very small range of possible over­ lap. The macrofauna contains a mixture of wild and domestic animals, herbivores and preda­ tors with sizes ranging from hare to buffalo. The microfauna is closely packed in a black or­ ganic-rich soil of predominantly dust sized particles. A feature of this soil is the vast number of tiny terrestrial snail shells it contains. The deposit represents continuous accumulation over several hundred years at least. Seeds, pollen and carbonised wood are present in the un­ disturbed deposit so that sequential dating will be possible. By contrast, recognisable insect cuticle is virtually absent though dung beetles, for example, are frequently seen in surface so­ lution cavities and must fall into the cave in fair numbers. Alignment of microfauna! longbones within the deposit is horizontal and parallel to the passage walls, so it is clear that the material was distributed by stream action. Much of the fauna has a wide geographic range, but throughout there are elements either endemic to the southern Cape or indicative of the prevailing vegetation type. INTRODUCTION As in the study of sedimentology, where modern analogues are used in the interpretation of ancient sedimentary rocks, so too can the study of recent unconsolidated cave fills assist in the interpreta­ tion of Plio-Pleistocene cave breccias. Similarly, just as major zones of sedimentation are subject to ongoing geological processes, so too may the pro­ cesses of cave formation continue during the accu­ mulation of cave deposits. Consequently, the re­ working of sediments can be as much a feature of the cave environment as any other situation where sediments accumulate. 105 It would be difficult to find modern analogues for the australopithecine bearing breccias within the Transvaal dolomite, because, although the caves within the dolomite vary· considerably in age, they are generally speaking old mature caves, and none to our knowledge contain significant re­ cent bone bearing deposits. Some l 500 km to the south, however, in the southern Cape coastal area near Bredasdorp (fig. 1) there is an extensive re­ gion of late Tertiary marine limestone deposited unconformably on wave cut pre-Cape shales. Just inland of the present coastline this limestone is only about 10 metres thick with cave systems de­ veloped at the contact with the underlying shale and linked to the surface by means of vertical shafts that vary from 1-1 0 m in diameter (fig. 2). These caves are still actively forming and have been accumulating partially surface-derived depos­ its for some considerable time. Figure I . Location of the cave Hot Pot on the Cape Provin­ cial Nature Conservation farm Dronkvlei. A row of low hills is indicated by the 400 foot contour. DESCRIPTION OF HOT POT Hot Pot cave 1s an extensive system linked to the surface in one place only by a narrow shaft at the apex of the domed roof of a large chamber; the shaft itself is about 5 m long. The name · derives from the hot, humid, stale air which makes it an unpleasant cave to examine. 106 A c D Figure 2. Sketch diagrams of ca_ve forms in the Bredasdorp limestone: A. sectional view of Hot Pot; B. plan view of Hot Pot, 'a' and ' b' are collecting sites; C. a more mature cave than A where the roof of the aven has collapsed completely; D . a further stage in cave formation where the whole system has become choked with fill. C and D are caves of the same form as A. Blocks indicate limestone, dashes cave fill. In addition to the remams of large animals which have fallen in from time to time since the opening of the cave, Hot Pot is apparently unique in the area in having an extensive and extremely rich microfauna! deposit. Much of this has been eroded and reworked by ground water breaking into empty side systems at present inaccessible to us. In the main passage of the system remnants of the deposit line the walls on either side. Further­ more, half a meter above the present surface of the deposit near the roof of the passage several small mammal bones are caught in the rough calcite protruberances on the passage walls. They indi­ cate that the passage was formerly choked with this microfauna! deposit because it is unlikely that these bones could have been lifted to their present position by groundwater without collapse of the near vertical sides of the still in situ deposit. Along the main passage the deposit extends for at least 30 m and is well over a metre deep in places. The undisturbed deposit that completely chokes the cave in the opposite direction from the entrance may also be more extensive. My recollec­ tion of the deposit from a visit about 15 years ago was that it had a moist firm consistency such that one would be able to take out an intact oriented block. During the time of sampling in December 1978, the deposit was powder dry, but it was appa­ rent that microfauna! long bones not only lay flat in the soil but were oriented with their long axes parallel to the walls of the cave passage. METHODS Sampling of the Deposit Samples were taken at two points . Point "a" (fig. 2A) is a break in the deposit where some had slumped into a side system. About 2 litres of microfauna! deposit was collected here. Point "b" (fig. 2B) is a blind side chamber which had been reworked by ground wafer. Here one walks on the deposit. Microfauna! remains are concentrated in surface depressions, and for some reason many larger bones accumulated in this part of the cave. All identifiable large bones were collected together with about a litre of microfauna! remains. Laboratory treatment of material Larger bones were scrubbed in clean water and then thoroughly soaked in dilute PVA clear sealer before drying on wire screens. The microfauna was sifted out of the cave soil. Handfuls of bones were carefully agitated in water to remove most of the adhering dirt. These were soaked in the PVA solu­ tion. The container was then emptied over a wire screen, the PVA passing into a second container for re-use. The cave earth was retained and screened for plant remains and grain characteris­ tics. RESULTS Macrofauna (table 1) The few remains of large animals such as buf­ falo, kudu and equid may have been introduced as isolated skeletal elements by a variety of fortuitous events. Most of the rest of this fauna, particularly the small antelope and domestic animals, almost certainly fell down the shaft and died in the cave, in many cases probably only after wandering about underground. A recent complete duiker ske­ leton lay some way down the main passage. The provenance of some of the smaller animals is equivocal; hare, large mole rat, and francolin might indicate occasional use of the cave by eagle owls, but the present sample is too small for a defi­ nite conclusion. Five barn owl bones of at least two individuals are probably remains of birds resident in the cave. These are bones of adult birds, and their presence could be explained in several ways, including the situation where a small predator such as a genet might have fallen uninjured into the cave and eaten an owl. TABLE 1 Macrofauna Species Syncerus ca.ffer Tragelaphus strep- siceros Common Name Buffalo Kudu Equus sp. Equid Tragelaphus scriptus Bush buck Alcelaphus Hartebeest buselaphus Ovis sp. Domestic sheep Sylvicapra grimmia Duiker Raphicerus ·campestris Steenbok Potamochoerus Bushpig porcus Sus sp. Domestic pig Lepus sp. Hare Bathyergus s. suillus Cape Dune Mole Felis !Jbica Cape Wild Cat Genetta genetta Herpestes cf. pulverulentus Tyto alba Francolinus sp. Genet Cape Grey Mongoose Barn owl Francolin Skeletal elements present lower premolar left ilium cervical vertebra humerus horn core partial skull, innominate lower jaw, carpal element, metatarsal epiphysis, two femora (different sizes), sca­ pula, cervical vertebra right and left jaw rami of different individuals, cervi­ cal vertebra, two femora, two tibiae humerus humerus partial skull scapula, jaw ramus maxilla, jaw ramus (both with teeth) complete skull jaw ramus two humeri of different in­ dividuals, two tarsometa­ tarsi of different individ­ uals, one phalanx coracoid, humerus Microfauna (tables 2, 3) The microfauna! deposit is extremely rich. With unimportant exceptions this assemblage is typical of the food remains of the barn owl, Tyto alba, which was without doubt the concentrating agent for this deposit. The relative importance of the various components of the microfauna in the diet of barn owls based on a sample of 200 crania is in­ dicated in Figure 3. BP - H 107 VL'EI RATS SHREWS GERBILS MOLE RATS LIZARDS GOLDEN MOLES BIRDS Figure 3: Histogram of abundance of microfauna] elements for a total of 200 individuals (all except birds based on crania only). Completeness of mammalian crania varies, the occipital region being absent in the majority. Re­ cent barn owl pellets contained intact crania as well as those in which the occipital portion was missing. Completeness also varies with postmor­ tem age, with older crania tending to fall apart very easily. Mammalian postcranial remains show very little damage, even to such delicate elements as scapulae. Of the non-mammalian microfauna the lizards and small birds are all typical barn owl prey. These all tend to become very fragmented with ad­ vancing postmortem age. Species Chrysochloris asiatica Crocidura sp. Macroscelididae Georhychus capensis Cryptomys hottentotus Otorrrys sp. Gerbillinae 4 species Rhinolophus sp. TABLE2 Mammalian Microfauna Common Name Cape Golden Mole Shrews Elephant Shrews Mole Rat Common Mole Rat Vlei Rats Gerbils Skull parts present 9 crania, 4 jaw rami 62 crania, 101 jaw rami one jaw ramus 4 crania 11 crania, 4 jaw rami 86 crania, 107 jaw rami 20 crania, 42 jaw rami Horseshoe Bat one jaw ramus 108 Species ? ? TABLE 3 Non-mammalian Microfauna Common Name Skeletal parts present Sm. passerine sterna, sacra, foot bones 6 birds individuals Tortoise one segment of bony cara- pace Pseudaspis cana Cordylus sp. Mole Snake dentary with teeth Spiny lizard angular, coracoid (different individuals) Agama sp. Koggelmander left maxilla and dentary, lizard right dentary (two animals) Mabuya sp. Skinks 3 right and 2 left dentaries, one right and 2 left maxil­ lae. All of different individ­ uals Snail shells Hundreds of tiny pulmonate snail shells oc­ curred in the deposit. According to Sirgel (pers. comm.), there are four genera present, namely Tro­ pidophora, Fauxulus, Trigonephrus and Trachycystis. These shells are perfectly preserved and are almost certainly wind-blown postmortem additions. Plant material Large fragments of carbonised woody material are present. Much of the cave earth consists of plant detritus, including well preserved seeds and pollens. Soil One kilogram of residual soil was coarse screened and the following percentages were re­ tained by the mesh sizes indicated: 1,7 mm 1,1 mm 0,6mm finer 10% 4% 15% 72% One hundred grams of the fine material screened further with the following results: 355 f.tm 21 % 250f.,l,m 21% 150 f.tm 32 % finer 24% was For the examination of the organic content 100 ml of dry material of the fine fraction was put in 20 % H 20 2 until bubbling ceased. Even this treatment did not entirely disaggregate the finer particles. About 1 ml of floating organic matter was scooped off with filter paper. The residue was allowed to settle out in the beaker and about 3 ml of the dense organic matter removed. The mineral grains were then washed as clean as possible and re­ tained. This material was then screened with the follow­ ing results: Floating organic component 355 f.tm: intact snail shells, seeds and fine plant detritus 250 f.tm: intact snail shells, large pollen grams and fine plant detritus 150 f.tm : pollen, and fine plant detritus Sinking organic component 250 f.tm: some discrete plant fragments, but most grains aggregates of finer particles 150 f.tm: similar except that discrete plant frag­ ments were distinctly elongate < 150 f.tm: (i.e. half this sample) still a lot of ad­ hesion of particles. Unrecognisable plant detritus. From the foregoing it is apparent that seeds and pollens are best obtained from the floating organic fraction provided disaggregation is reasonably com­ plete. To examine the characteristics of the mineral grains 17 g of original limestone were picked out of the soil. This material was dissolved in 10 % for­ mic acid and 1 g of resistant sandy material recov­ ered. As is typical of sands from this sort of deposi­ tional setting, the grains are predominantly quartzitic, poorly sorted (±2 mm down to 0,15 mm) and vary from angular to rounded. There are sparse, fragmentary marine microfossils. In view of the above it is not possible to distin­ guish between sand derived more or less in situ from re-solution of the limestone and surface de­ rived sand which is effectively from the same source. DISCUSSION AND CONCLUSIONS This site has excellent potential for a controlled excavation. It will provide a comprehensive record of barn owl diet for the area, a record of the large animal fauna dating from the present to recent prehistoric times and a similar record for the flora. Cave formation and depositional processes can be studied, and it should prove possible to assess the rate of accumulation of the deposit. ACKNOWLEDGEMENTS Collecting was made possible through the good offices of Dr. Steven Craven of Groote Schuur Hospital , Cape Town. Nature Conservation staff were hospitable and helpful in the field . The South African Spelaeological Association, Trans­ vaal Section, lent the necessary caving ladder. Mr. W.F. Sir­ gel, Dept. of Zoology, University of Stellenbosch, identified the snails .