Boomplaas Cave

Boomplaas Cave is a key late Quaternary archaeological and paleoenvironmental archive for southern Africa’s Cape Floristic Region. This region comprises an area of ~88,000 km² along the southern and western-most portion of southern Africa, including the mountains of the Cape Fold Belt and the coastal lowlands. The Cape Floristic Region is best known for its spectacular floristic diversity, including the world’s highest frequency of endemic plant species (Goldblatt and Manning Reference Goldblatt and Manning2002; Linder Reference Linder2003), but to archaeologists it is also well known for its Middle and Later Stone Age archaeological sites that feature prominently in our understanding of modern human origins, with some of the best-known sites including the Klasies River Mouth caves, Blombos Cave, and the Pinnacle Point caves.

Boomplaas Cave is situated at an elevation of ~700 m above sea level within the cliffs of a limestone seam on the southern foothills of the Swartberg mountain range, approximately 60 m above the Cango Valley. The east–west trending Swartberg range forms the northern boundary of the intermontane basin known as the Klein Karoo, with the Outeniqua range marking its southern boundary 50 km to the south. The lowlands of the Klein Karoo, which sit in the rain-shadow of the Outeniquas, are a semi-desert; rainfall is higher in the mountainous uplands and Boomplaas Cave receives around 400 mm annual precipitation. Compared with much of the Klein Karoo, the Cango Valley is well-watered by streams draining from the flanks of the Swartberg and into the eastward-flowing Grobelaars River (at the foot of Boomplaas Cave) and the westward-flowing Matjes River (10 km west of Boomplaas Cave).

The vegetation in the immediate vicinity of Boomplaas Cave is part of a transitional shrubland whose component species vary in relation to temperature and rainfall gradients from the valley floor up the slopes of the Swartberg (see Vlok and Schutte-Vlok [Reference Vlok and Schutte-Vlok2010] for a detailed summary). The transitional shrublands are dominated by single shrub species, though grasses and short-lived herbs flourish after fires. In the low-lying areas just south of Boomplaas Cave occurs a shrubby habitat known as renosterveld, characterized by the renosterbos (Elytropappus rhinocerotis) and a sparse understory of grasses. Along watercourses and ravines in the Cango Valley are more densely wooded habitats that include sweet thorn trees (Acacia karroo) and ironwood (Olea spp.) among others (Moffett and Deacon Reference Moffett and Deacon1977). The transitional shrublands give way to fynbos habitats – hard-leaved evergreen shrublands typically dominated by restios, ericas, and proteas – as one moves up the slopes of the Swartberg. These include a grassy fynbos habitat known as waboomveld, indicated by the presence of Protea nitida (waboom or wagon tree) and relatively abundant grasses, just north of Boomplaas. The grasses that occur in the vicinity of Boomplaas include a mix of C₃ (cool-season) and C₄ (warm-season) species, reflecting the fact that rainfall is fairly evenly distributed through the year.

Excavations conducted by Hilary Deacon (University of Stellenbosch) from 1974 to 1979 uncovered a stratified sequence extending to 5 m in depth and spanning the past >65,000 years (H. J. Deacon 1979, Reference Deacon1995; H. J. Deacon and Brooker Reference Deacon and Brooker1976; H. J. Deacon et al. Reference Deacon, Deacon, Scholtz, Thackeray, Brink and Vogel1984; see also J. Deacon Reference Deacon1984). Deacon (Reference Deacon1979) organized the stratigraphy according to a hierarchical scheme of stratigraphic members, units, and sub-units. We use the coarser-scale members in our analyses primarily because these stratigraphic aggregates provide larger sample sizes. Our goal in these analyses is to illustrate the application of certain techniques, so finer-scale stratigraphic and temporal control – which might be important if our goal were to address particular paleoenvironmental questions – is not needed here.

The chronology of the Boomplaas Cave deposits is supported by radiocarbon dates (primarily on charcoal) for the middle to upper portions of the sequence and a combination of amino acid racemization (AAR) on ostrich eggshell (Miller et al. Reference Miller, Beaumont and Deacon1999) and U-series ages on speleothems (Vogel Reference Vogel, Tobias, Raath, Maggi-Cecchi and Doyle2001) for the lower section. The Boomplaas Cave chronology is summarized in Table 4.1. The lowest dated member (OCH) is associated with a broad range of age estimates but it includes Middle Stone Age artifacts attributed to the Howieson’s Poort industry, which has been dated elsewhere in southern Africa by optically stimulated luminescence to ~59 to 66 ka (Jacobs and Roberts Reference Jacobs and Roberts2017). The basal member (LOH) is estimated to date to 80 ka (H. J. Deacon Reference Deacon1979) but this is not supported by any radiometric age estimates.

Boomplaas was excavated using 3 mm mesh screens, though select 1×1 m excavation squares were sieved through 2 mm mesh screens to enhance recovery of the microfauna (Avery Reference Avery1982). The recovered material has been reported in numerous publications spanning the past several decades. These include reports on the cultural remains (H. J. Deacon et al. Reference Deacon, Deacon and Brooker1976; H. J. Deacon et al. Reference Deacon, Deacon, Brooker and Wilson1978; J. Deacon Reference Deacon1984), the chronology (Miller et al. Reference Miller, Beaumont and Deacon1999; Vogel Reference Vogel, Tobias, Raath, Maggi-Cecchi and Doyle2001), fossil charcoal and pollen (H. J. Deacon et al. Reference Deacon, Scholtz, Daitz, Deacon, Hendey and Lambrechts1983; Scholtz Reference Scholtz1986), micromammals (Avery Reference Avery1982, Reference Avery2004; Thackeray Reference Thackeray1987), macromammals (Brink Reference Brink1999; Driesch and Deacon Reference Driesch and Deacon1985; Faith Reference Faith2013a; Klein Reference Klein1978, Reference Klein and Cruz-Uribe1983), and isotope geochemistry of ungulate tooth enamel (Sealy et al. Reference Sealy, Lee-Thorp, Loftus, Faith and Marean2016).

Table 4.2 reports Avery’s (Reference Avery1982) taxonomic abundances (minimum number of individuals = MNI) for the rodents and insectivores (shrews, elephant shrews, and golden moles) from Boomplaas Cave. The sample includes more than 30,000 individuals distributed across twenty-five species. Based primarily on an assessment of the ecology of the prey species, most of which are nocturnal, Avery (Reference Avery1982) suggests that barn owls (Tyto alba) were the likely accumulators of the assemblage, an argument consistent with the presence of modern barn owl roosts in rockshelters adjacent to Boomplaas Cave. The micromammals are especially dense in deposits lacking archaeological remains (H. J. Deacon Reference Deacon1979), suggesting they were deposited when the cave was unoccupied by people.

The Boomplaas macromammal data are derived from specimen counts (typically referred to as number of identified specimens, or NISP) provided by Faith (Reference Faith2013a), reported here in Table 4.3. Note that Faith (Reference Faith2013a) did not examine the faunas from the uppermost pastoralist occupation (member DGL), which is dominated by sheep. The sample includes more than 6,400 specimens distributed across thirty-six non-overlapping taxa, though many of our analyses focus specifically on the ungulates (>2,600 specimens distributed across twenty-one non-overlapping taxa). Given the highly fragmentary nature of the Boomplaas Cave material, which rendered most specimens unidentifiable to lower taxonomic groups, the vast majority of taxonomic identifications for ungulates are based on dental remains. Analysis of bone surface modifications of those specimens corresponding in size to the ungulate taxa (>5 kg) at Boomplaas Cave indicates a complex taphonomic history of bone accumulation (Faith Reference Faith2013a). The mammals from the bottom of the sequence were accumulated primarily by carnivores – leopards (Panthera pardus) being a likely candidate – with large raptors, probably the Cape eagle owl (Bubo capensis), also introducing remains belonging to the smallest bovids (Oreotragus oreotragus and Raphicerus spp.). From members BOL to GWA, there are variable amounts of bone accumulation related to people, carnivores, and raptors, with the anthropogenic component related mainly to the largest ungulate species. And in the upper members (CL and above), people accumulated most of the faunal remains. This complex taphonomic history poses some challenges for interpreting the environmental implications of the Boomplaas macromammals, and we discuss how this might be dealt with in subsequent chapters.

Homestead Cave

Homestead Cave provides perhaps the most detailed late Quaternary mammal sequence for the Great Basin (Grayson Reference Grayson2006, Reference Grayson2011), the vast region of internal drainage in the arid western United States. Homestead Cave is located at the northwestern-most spur of the Lakeside Mountains just west of the Great Salt Lake in north-central Utah. This low-lying spur, known as Homestead Knoll, is a rocky promontory lacking active springs or perennial streams and receiving very little rainfall throughout the year (~225 mm). The cave is formed within a small limestone ridge and sits at an elevation of 1,406 m, approximately 100 m above the valley floor. To the immediate west and northwest is the saline playa of Pleistocene Lake Bonneville, the pluvial lake that formerly covered much of western Utah until the Pleistocene came to an end. Although the playa is barren, the vegetation on the knoll itself is dominated by grasses and shrubs – the dominants being shadscale (Atriplex confertifolia) and horsebrushes (Tetradymia spp.) – with a few scattered junipers (Juniperus osteosperma). Greasewood (Sarcobatus vermiculatus) and big sagebrush (Artemisia tridentata) are common on the valley floor, along with invasive cheat grasses (Bromus spp.).

Excavations at Homestead Cave were directed by David Madsen (Utah Geological Survey) in 1993 (Madsen Reference Madsen2000). His team excavated a 1 × 1 m square down to bedrock – at a depth of ~2.7 m – providing a finely stratified sequence that begins ~13,000 years ago and continues into historic times. The stratigraphy is aggregated according to eighteen analytical units, from Stratum I at the base to Stratum XVIII at the top (Table 4.4). The original chronology reported by Madsen (Reference Madsen2000) is provided by a series of twenty-one radiocarbon dates on various organic materials (e.g., fecal pellets, hackberry endocarps, charcoal), with an additional eighty radiocarbon dates obtained on kangaroo rat (Dipodomys spp.) femora more recently provided by Terry and Novak (Reference Terry and Novak2015). For the sake of simplicity, we report Madsen’s (Reference Madsen2000) chronology in Table 4.4.

Excavated deposits were passed through 1/4″ (6.4 mm), 1/8″ (3.2 mm), and 1/16″ (1.6 mm) mesh screens, from which organic and (rare) cultural remains were recovered. Madsen’s (Reference Madsen2000) monograph, which includes contributions from a variety of specialists, provides an excellent account of the excavated materials (see also Madsen et al. Reference Madsen, Rhode and Grayson2001). There are numerous other reports on Homestead Cave, including studies of the fecal pellets from woodrats (Neotoma spp.) (Smith and Betancourt Reference Smith and Betancourt2003) and artiodactyls (Broughton et al. Reference Broughton, Byers, Bryson, Eckerle and Madsen2008), fishes (Broughton Reference Broughton2000; Broughton et al. Reference Broughton, Madsen and Quade2000, Reference Broughton, Cannon, Arnold, Bogiatto and Dalton2006), mammals (Grayson Reference Grayson1998, Reference Grayson2000b; Grayson and Madsen Reference Broughton, Madsen and Quade2000; Lyman and O’Brien Reference Lyman and O’Brien2005; Rowe and Terry Reference Rowe and Terry2014; Terry Reference Terry2007, Reference Terry2010a; Terry and Rowe Reference Terry and Rowe2015; Terry et al. Reference Terry, Li and Hadly2011), and the chronology (Terry and Novak Reference Terry and Novak2015).

The very limited evidence for human occupation of Homestead Cave, in contrast to sites elsewhere in the Bonneville Basin, is probably related to the lack of available water. But this did not detract from the suitability of the cave for owls. Roosting screech owls (Megascops kennicottii) and dense piles of owl pellets were observed in the cave when excavations began (Madsen Reference Madsen2000), and owl pellets in various states of decay were found throughout the sequence, with many of the recovered fossils having remains of pellets adhering to them (Grayson Reference Grayson and Madsen2000a, Reference Grayson2000b). Like the micromammals from Boomplaas Cave, owls accumulated the vast majority of the Homestead faunal assemblage, which is dominated by rodents and lagomorphs. There are rare remains of large mammals, including artiodactyls and carnivores. These are represented primarily by small bones of the hands and feet (e.g., carpals, phalanges) and are thought to have been introduced by woodrats.

Our analyses of the Homestead Cave faunas make use of Grayson’s (Reference Grayson and Madsen2000a) specimen counts (NISP) for rodents and lagomorphs (Table 4.5). Grayson’s (Reference Grayson and Madsen2000a) data are based on identification of all mammals from the 1/4″ (6.4 mm) and 1/8″ (3.2 mm) sample fractions from fourteen of the eighteen stratigraphic units. Only the kangaroo rats (Dipodomys spp.) from Stratum X were identified so this stratum is not considered here. As is clear from Table 4.5, sample sizes are massive, with counts for individual assemblages ranging from 1,045 in Stratum XVIII – a solid figure by most paleozoological standards – to a whopping 28,525 in Stratum IV. These impressive samples are precisely why the Homestead Cave faunas feature so prominently in the biogeographic histories of Great Basin mammals.

Summary

Boomplaas Cave and Homestead Cave are, in some important ways, ideal collections with which to illustrate the variety of analytical techniques described in subsequent chapters of this volume. They are well studied and well known, they produced large samples for each of several chronologically tightly controlled stratigraphically delimited assemblages, the collections represent temporal spans known to include major episodes of climatic variability, and the taphonomic histories of the assemblages of each are sufficiently well known as to not introduce insurmountable biases or skewing of paleoenvironmental signals.

Not all collections of ancient faunal remains provide such exemplary samples as Boomplaas Cave and Homestead Cave, so do not be misled into thinking all collections are of equal value. As should be clear from Chapter 3 and this chapter, not only do analyzing and interpreting all collections require certain analytical assumptions, some collections may simply not be amenable to some kinds of analysis for any of a plethora of reasons. We thus call upon a variety of collections to illustrate particular analytical techniques or to underscore certain points in subsequent pages. It is our hope that, as we indicated earlier, in frequently referring to the same collections the reader need not focus too much on the particulars of those collections but instead can focus on the techniques under discussion. With the background of this and preceding chapters in hand, it is now time to turn to the focus of the volume, the analytical techniques that have been used to manipulate faunal data in such a way as to reveal their paleoenvironmental implications.