Ronald J. Clarke

Latest information on Sterkfontein's Australopithecus skeleton and a new look at Australopithecus

After a decade of careful excavation, it is now possible to explain how the skeleton came to be in that isolated position in the cavern. Furthermore, it is apparent that the fossil does not belong to either Australopithecus africanus or to A. afarensis, but to an individual belonging to, or closely affiliated to, the second Australopithecus species that is represented in Sterkfontein Member 4 and Makapansgat.

The new hominid skeleton from Sterkfontein, South Africa: age and preliminary assessment

A new hominid skeleton from Sterkfontein Member 2 attaches to foot bones recovered from loose blocks during the 1980s and first described in 1995. Several flowstone horizons are present above and below the skeleton and have given clear palaeomagnetic signatures. Five changes in magnetic polarity have been identified; when constrained by the available biostratigraphy, this sequence can be placed confidently between 3.22 and 3.58 Ma. Interpolation of sedimentation rates over the small intervals between reversals allows this range to be reduced to 3.30-3.33 Ma. The skeleton is thus the oldest yet discovered and is considered to belong to a species of Australopithecus other than africanus. Copyright

Australopithecus from Sterkfontein Caves, South Africa

Since the discovery by Robert Broom of the first adult Australopithecus at Sterkfontein in 1936, a large quantity of fossil remains of this genus, consisting of crania, teeth and postcranial bones, has been excavated from those cave infills. They have generally been considered as belonging to one species, Australopithecus africanus, but there is now abundant proof that a second species is represented by many of the fossils. This second species should be classified as Australopithecus prometheus, the name given by Raymond Dart in 1948 to such fossils from Makapansgat (MLD 1 and MLD 2). A. prometheus is distinguished from A. africanus by having a more vertical occiput, larger, bulbous-cusped cheek teeth, a flatter face, lower frontal squame, and sagittal crest in the males. An almost complete skeleton of Australopithecus (StW 573) from an early deposit in the cave belongs to this second species, and for the first time this discovery made it possible to indisputably associate postcranial anatomy with specific cranial anatomy. It is also now possible to clearly distinguish males and females of each species, and to state with conviction that StW 53, a cranium excavated in 1976 and widely identified as Homo habilis, is in fact a male A. africanus, virtually the same as the TM 1511 cranium found by Broom 40 years earlier.

Newly discovered fossil- and artifact-bearing deposits, uranium-series ages, and Plio-Pleistocene hominids at Swartkrans cave, South Africa.

We report on new research at Swartkrans Cave, South Africa, that provides evidence of two previously unrealized artifact- and fossil-bearing deposits. These deposits underlie a speleothem dated by the uranium-thorium disequilibrium technique to 110,000+/-1,980 years old, the first tightly constrained, geochronological date available for the site. Recovered fauna from the two underlying deposits-including, prominently, the dental remains of Paranthropus (Australopithecus) robustus from the uppermost layer (Talus Cone Deposit)-indicate a significantly older, late Pliocene or early Pleistocene age for these units. The lowest unit (LB East Extension) is inferred to be an eastward extension of the well-known Lower Bank of Member 1, the earliest surviving infill represented at the site. The date acquired from the speleothem also sets the maximum age of a rich Middle Stone Age lithic assemblage.

Letter to the editor: Response to Holloway and Broadfield's critique of our reconstruction of the Taung virtual endocast.

Without providing any support for their claim, Holloway and Broadfield (H&B) assert that ‘‘the Falk and Clarke (2007) reconstruction of Taung miscalculates the midsagittal plane, resulting in a significant reduction in cranial capacity that may call into question the taxonomic significance of the fossil’’ (Holloway and Broadfield, 2011:322). We agree that the 22 cm difference in the capacities of our respective reconstructions of the Taung endocast may be due largely to differences in our reconstructed midsagittal planes; however, we have good reason to reject the assertion that our plane is miscalculated. The Taung fossil (Australopithecus africanus) consists of a natural endocast that reproduces external morphology from most of the right and part of the left hemispheres of the brain, a separate portion of the fossilized face that articulates with the endocast, and a mandible that occludes with the maxillary dentition in the face. The right temporal and both frontal poles are separated from the endocast and embedded in the back of the facial fragment. In 2007, we published a description of a new virtual endocast of Taung in AJPA and provided a cranial capacity estimate of 382 cm, which is 22 cm smaller than an estimate of 404 cm published by Holloway in 1970. Our reconstruction incorporated, for the first time, both frontal lobes, which were extracted manually from the back of the facial fragment, imaged, and attached electronically to the posterior portion of the endocast, which had been reconstructed by mirror imaging the right hemisphere of the separate natural endocast. We, thus, did not mirror image Taung’s frontal polar region as H&B claim, and the slight asymmetry (a left frontal petalia) in that part of our reconstruction (Falk and Clarke, 2007: Fig. 2) is not surprising because asymmetries in the frontal polar region occur frequently in apes and more often in humans. More to the point, the slight left frontal petalia reproduced by our reconstruction of Taung’s endocast has recently been confirmed independently from a 3D-CT reconstruction of Taung’s frontal lobes (Fig. 1). Taung’s natural endocast has a small gap at the midline of the right cerebellar region, which (since it was missing) could not be mirror imaged. A gap was therefore left in this part of the mirrored natural endocast, which was subsequently filled manually (modeled) with Plasticine by DF. This was done by using a mirrored bony fragment of the occipital condyle that was attached to the natural endocast and a trace of an enlarged right marginal sinus as guidelines (see Falk and Clarke, 2007 for details). Because enlarged occipital-marginal (O/M) sinuses of australopithecines are more often present unilaterally than bilaterally, and on the right rather than the left side, DF decided not to mirror the traces of Taung’s enlarged right O/M sinus. For our article, we therefore did not calculate a midsagittal plane around which to mirror image either this hand-reconstructed region or the frontal polar region, and thus the asymmetries in these parts of our reconstruction are not attributable to errors in mirror imaging. Nevertheless, Holloway and Broadfield (H&B) suggest that we 1) mirror imaged Taung’s frontal lobes and 2) did so incorrectly because we failed to accurately define the midsagittal plane around which the mirror imaging was supposedly performed: ‘‘A virtual reconstruction of Taung must assume perfect symmetry, a feature called into question here in Taung’s most recent reconstruction by Falk and Clarke (2007)’’ (H&B, 2011:319). . ..‘‘The authors rely heavily on mirror imaging to produce the final endocast, but the reconstruction displays a visible lack of symmetry between right and left sides’’ (H&B, 2011:319). . ..‘‘A careful examination of Falk and Clarke’s (2007) Figure 2 (see Fig. 5) indicates that a lack of symmetry exists between left and right cerebral hemispheres. . .. issues of symmetry include. . .a left prefrontal that is not an exact duplicate of the actual right side’’ (H&B, 2011:320-322). . ..‘‘The Falk and Clarke (2007) reconstruction of Taung miscalculates the midsagittal plane. . . Again, it is mandatory that the missing left half be exactly the same as the present right half ’’ (H&B, 2011:322). Although we did not compute a midsagittal plane for Taung’s frontal polar region, we did compute one for the separate natural endocast so that we could mirror image its nearly complete right hemisphere. As H&B note, the reconstruction of the midsagittal plane is critical for obtaining an accurate cranial capacity. This is true because the position of the midsagittal plane of an object limits its volume on one side of that plane and therefore constrains the mirrored (doubled) volume. Our procedures for mirror imaging the right hemisphere of Taung’s natural endocast were described in detail, and were performed with advanced computer technology and software (Falk and Clarke, 2007). After an automated digitization process that captured 3D data from all surfaces of the Taung natural endocast, we sequentially digitized all of the points on the obvious midline (Fig. 1) that courses along the endocast’s dorsal surface (including the sagittal suture, SS) and continues ventrally midway between the orbits and medial to the frag-

A hominin scaphoid from Sterkfontein, Member 4: morphological description and first comparative phenetic 3D analyses.

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In situ 3D Digitization of the "Little Foot" Australopithecus skeleton from Sterkfontein

e see front matter Published by Elsevie doi:10.1016/j.jhevol.2011.06.001 Since the discovery of the Taung child and the naming of the genus Australopithecus (Dart, 1925), South African sites have produced a considerable array of hominin1 fossils. However, one anatomical region that is substantially under-represented in the South African hominin fossil record is the wrist, which is currently represented by only two carpal bones: a right capitate (TM 1526) and a right triquetrum (SKX 3498). The capitate, discovered by Robert Broom during the late 1930s in bone breccia fromMember 4 at Sterkfontein, is typically referred to Australopithecus africanus (Broom and Schepers, 1946). The triquetrum was recovered from Member 2 at Swartkrans during the 1979e1986 excavations but has not been attributed to a particular hominin taxon (Susman, 1988; Kivell, 2011). Although SKX 3498 is broadly similar to that of African apes and humans (Kivell, 2011), TM 1526 shows a mix of primitive and derived features similar to that observed in several Australopithecus capitates from East Africa as well as the capitate of Homo floresiensis from Flores, Indonesia (Broom and Schepers, 1946; Lewis, 1973; Bush et al., 1982; McHenry, 1983; Ward et al., 1999a,b, 2001; Tocheri et al., 2007, 2008). Recently, a well-preserved hominin scaphoid was identified by one of us (JMK) while analyzing faunal remains from Sterkfontein (Kibii, 2004). This fossil carpal bone is accessioned as Stw 618 and is

Cranial vault thickness variation and inner structural organization in the StW 578 hominin cranium from Jacovec Cavern, South Africa

Here we describe the methodology we used to digitize an excavation site of a very ancient fossil hominid in South Africa, which has been recently dated using cosmogenic techniques. We detail the practical aspects of acquiring 3D views with a laser range scanner and the post-processing computer graphics pipeline required to obtain an accurate 3D representation.

Stratigraphy, artefact industries and hominid associations for Sterkfontein, Member 5

The Sterkfontein Caves site is one of the richest early hominin fossil localities in Africa. More specifically, the fossiliferous deposits within the lower-lying Jacovec Cavern have yielded valuable hominin remains; prominent among them is the Australopithecus partial cranium StW 578. Due to the fragmentary nature of the braincase, the specimen has not yet been formally assigned to a species. In this context, we employ microtomography to quantify cranial thickness and composition of StW 578 in order to assess its taxonomic affinity. As comparative material, we investigate 10 South African hominin cranial specimens from Sterkfontein (StW 505, Sts 5, Sts 25, Sts 71), Swartkrans (SK 46, SK 48, SK 49) and Makapansgat (MLD 1, MLD 10, MLD 37/38), attributed to either Australopithecus or Paranthropus, as well as 10 extant human and 10 extant chimpanzee crania. Thickness variation in and structural arrangement of the inner and outer cortical tables and the diploë are automatically assessed at regular intervals along one parasagittal and one coronal section. Additionally, topographic cranial vault thickness distribution is visualized using color maps. Comparisons highlight an absolutely and relatively thickened condition of the StW 578 cranial vault versus those of other South African Plio-Pleistocene hominins. Moreover, in StW 578, as well as in the Australopithecus specimens Sts 5 and Sts 71 from Sterkfontein, the diploic layer contributes substantially to cumulative vault thickness (i.e., >60%). Within the comparative sample investigated here, StW 505 and Sts 71 from Sterkfontein Member 4, both attributed to Australopithecus, most closely resemble StW 578 in terms of cranial vault thickness values, tissue proportions, and two- and three-dimensional distributions. Including additional Plio-Pleistocene Australopithecus and Paranthropus crania from South and East Africa in future studies would further help establish morphological variability in these hominin taxa.