John Francis Thackeray

Three-dimensional molar enamel distribution and thickness in Australopithecus and Paranthropus

Thick molar enamel is among the few diagnostic characters of hominins which are measurable in fossil specimens. Despite a long history of study and characterization of Paranthropus molars as relatively ‘hyper-thick’, only a few tooth fragments and controlled planes of section (designed to be proxies of whole-crown thickness) have been measured. Here, we measure molar enamel thickness in Australopithecus africanus and Paranthropus robustus using accurate microtomographic methods, recording the whole-crown distribution of enamel. Both taxa have relatively thick enamel, but are thinner than previously characterized based on two-dimensional measurements. Three-dimensional measurements show that P. robustus enamel is not hyper-thick, and A. africanus enamel is relatively thinner than that of recent humans. Interspecific differences in the whole-crown distribution of enamel thickness influence cross-sectional measurements such that enamel thickness is exaggerated in two-dimensional sections of A. africanus and P. robustus molars. As such, two-dimensional enamel thickness measurements in australopiths are not reliable proxies for the three-dimensional data they are meant to represent. The three-dimensional distribution of enamel thickness shows different patterns among species, and is more useful for the interpretation of functional adaptations than single summary measures of enamel thickness.

Early Homo at Kromdraai B: probabilistic and morphological analysis of the lower dentition

Kromdraai B, situated less than 2 km east of Sterkfontein, in the Gauteng province of South Africa, has yielded 27 specimens, attributed to a single Plio-Pleistocene hominid species, including the type specimen of Paranthropus (Australopithecus) robustus. By using resampling and morphological analysis, and after considering the most diagnostic features that have been used in the past for the lower dentition, we here suggest that one specimen from Kromdraai B, KB 5223, is clearly distinct from

Probabilities of conspecificity.

G. Suwa et al. and E. Delsons News and Views address one of the most contentious issues in palaeoanthropology, that of the boundaries (if any) between hominid species, in the context of an exciting new fossil from Konso in Ethiopia. Suwa et al. attribute this specimen to Australopithecus boisei, but note that it has some similarities to the South African robust australopithecines first described by Robert Broom more than 50 years ago.

The enamel-dentine junction (EDJ) in the post-canine dentition of Australopithecus africanus (Sts52): assessment of intra-individual metameric and antimeric variation

We used micro‐computed tomography and virtual tools to study metric and morphological features at the enamel–dentine junction and on the outer enamel surface in the postcanine dentition of an exceptionally well‐preserved maxilla and mandible of an early hominin. The fossil, Sts 52 from Sterkfontein, South Africa, is attributed to Australopithecus africanus and is about 2.5 million years old. For comparative purposes in this exploratory study, we also used micro‐computed tomography to analyse the dentition of a common chimpanzee (Pan troglodytes), a pygmy chimpanzee (Pan paniscus) and three extant humans. Metameric variation of the 3D enamel–dentine junction in the two chimpanzee mandibles was much smaller than in extant humans. Variation in metameric shape was high and complex. Notably, the mandibular metameric variation in extant humans can be greater within individuals, as compared with variation between individuals, with differences in shape appearing greater for M2 compared with M1. We recommend the use of a new approach in which individual metameric variation is systematically assessed before making inferences about differences between fossil hominin species. The fossil hominin examined in this study showed a metameric pattern of mandibular variation in shape that was comparable to the pattern seen in two chimpanzees. This degree of metameric variation appeared relatively small compared with the much larger patterns of variation observed within and between extant humans.

Disproportionate Cochlear Length in Genus Homo Shows a High Phylogenetic Signal during Apes' Hearing Evolution.

Changes in lifestyles and body weight affected mammal life-history evolution but little is known about how they shaped species’ sensory systems. Since auditory sensitivity impacts communication tasks and environmental acoustic awareness, it may have represented a deciding factor during mammal evolution, including apes. Here, we statistically measure the influence of phylogeny and allometry on the variation of five cochlear morphological features associated with hearing capacities across 22 living and 5 fossil catarrhine species. We find high phylogenetic signals for absolute and relative cochlear length only. Comparisons between fossil cochleae and reconstructed ape ancestral morphotypes show that Australopithecus absolute and relative cochlear lengths are explicable by phylogeny and concordant with the hypothetized ((Pan,Homo),Gorilla) and (Pan,Homo) most recent common ancestors. Conversely, deviations of the Paranthropus oval window area from these most recent common ancestors are not explicable by phylogeny and body weight alone, but suggest instead rapid evolutionary changes (directional selection) of its hearing organ. Premodern (Homo erectus) and modern human cochleae set apart from living non-human catarrhines and australopiths. They show cochlear relative lengths and oval window areas larger than expected for their body mass, two features corresponding to increased low-frequency sensitivity more recent than 2 million years ago. The uniqueness of the “hypertrophied” cochlea in the genus Homo (as opposed to the australopiths) and the significantly high phylogenetic signal of this organ among apes indicate its usefulness to identify homologies and monophyletic groups in the hominid fossil record.

Morphoarchitectural variation in South African fossil cercopithecoid endocasts

Despite the abundance of well-preserved crania and natural endocasts in the South African Plio-Pleistocene cercopithecoid record, which provide direct information relevant to the evolution of their endocranial characteristics, few studies have attempted to characterize patterns of external brain morphology in this highly successful primate Superfamily. The availability of non-destructive penetrating radiation imaging systems, together with recently developed computer-based analytical tools, allow for high resolution virtual imaging and modeling of the endocranial casts and thus disclose new perspectives in comparative paleoneurology. Here, we use X-ray microtomographic-based 3D virtual imaging and quantitative analyses to investigate the endocranial organization of 14 cercopithecoid specimens from the South African sites of Makapansgat, Sterkfontein, Swartkrans, and Taung. We present the first detailed comparative description of the external neuroanatomies that characterize these Plio-Pleistocene primates. Along with reconstruction of endocranial volumes, we combine a semi-automatic technique for extracting the neocortical sulcal pattern together with a landmark-free surface deformation method to investigate topographic differences in morphostructural organization. Besides providing and comparing for the first time endocranial volume estimates of extinct Plio-Pleistocene South African cercopithecoid taxa, we report additional information regarding the variation in the sulcal pattern of Theropithecus oswaldi subspecies, and notably of the central sulcus, and the neuroanatomical condition of the colobine taxon Cercopithecoides williamsi, suggested to be similar for some aspects to the papionin pattern, and discuss potential phylogenetic and taxonomic implications. Further research in virtual paleoneurology, applied to specimens from a wider geographic area, is needed to clarify the polarity, intensity, and timing of cortical surface evolution in cercopithecoid lineages.

Upper third molar internal structural organization and semicircular canal morphology in Plio-Pleistocene South African cercopithecoids

Despite the abundance of cercopithecoids in the fossil record, especially in South Africa, and the recent development of morphometric approaches, uncertainties regarding the taxonomic identification of isolated cranio-dental specimens remain. Because cercopithecoids, nearly always found in stratigraphic association with hominin remains in Plio-Pleistocene deposits, are considered as sensitive ecological and chronological biomarkers, a significant effort should be made to clarify their palaeobiodiversity by assessing additional reliable morphological diagnostic criteria. Here we test the relevance of both molar crown internal structure and bony labyrinth morphology for discrimination of fossil cercopithecoid species. We use microtomographic-based 3D virtual imaging and quantitative analyses to investigate tooth endostructural organization and inner ear shape in 29 craniodental specimens from the South African sites of Kromdraai, Makapansgat, Sterkfontein and Swartkrans and provide the first detailed description of the internal structural condition characterizing this Plio-Pleistocene primate assemblage. Our preliminary results show that enamel-dentine junction morphology could be informative for discriminating highly autapomorphic taxa such as Theropithecus, while semicircular canal shape is tentatively proposed as an efficient criterion for diagnosing Dinopithecus ingens. Further research in virtual paleoprimatology may contribute to the identification of unassigned isolated fossil remains and shed new light on the internal craniodental morphology of extinct primate taxa.

Morphometric comparisons between crania of Late Pleistocene Homo sapiens from Border Cave (BC 1), Tuinplaas (TP 1) and modern southern African populations

Two Late Pleistocene fossil specimens, Border Cave hominin 1 (BC 1) and Tuinplaas hominin 1 (TP 1), are thought to be among the earliest known “anatomically modern” Homo sapiens in southern Africa. Cranial measurements of these two specimens are compared against corresponding data from modern KhoeSan and non-KhoeSan crania, representing respectively “Bushman” and Bantu-speaking populations from southern Africa. Morphometric comparisons between BC 1 and modern samples, and between TP 1 and the same samples, are undertaken using least squares linear regression analyses. BC 1 appears to be most similar to modern Bantu-speaking populations, whereas TP 1 is most similar to KhoeSan and Xhosa which are known to have interacted in recent millennia. The slopes of the regression lines are used as a basis for suggesting that both TP 1 and BC 1 are males.

Temporal lines and open sutures revealed on cranial bone adhering to matrix associated with Sts 5 ( Mrs Ples ), Sterkfontein, South Africa

An almost complete cranium of Australopithecus africanus (Sts 5, nicknamed ‘‘Mrs Ples,’’ Fig. 1), dated at 2.15 million years (Partridge, 2005; Thackeray and Dupont, 2006), was found in 1947 at Sterkfontein by Robert Broom and John Robinson at a time when the caves were being blasted by dynamite for limestone (Broom, 1947a, b). Initially the Historical Monuments Commission had denied Broom permission to excavate the site on account of the allegation that he was not paying attention to stratigraphy. However, in Broom’s (1950) opinion, clear stratigraphy was absent; the cave deposits had formed as a talus cone (Clarke, 1994) that would have been disturbed in prehistory as a consequence of episodes of erosion, as well as deposition. Deliberately breaking the law, Broom worked with lime miners in an attempt to discover hominin fossils to supplement those that he had found since 1936 (Broom and Schepers, 1946). Immediately after the discovery of Sts 5, Broom summoned a reporter from The Star newspaper and a valuable photograph was recorded (Broom, 1947b). Two components of the cranium, both encased in calcified sediments, were taken to the Transvaal Museum where they were mechanically prepared using a hammer and chisel. In the course of this preparation, six blocks of breccia were detached, each of which retained a thin (circa 1 mm) layer of cranial bone. They were formally reported only fifty years after the initial discovery (Thackeray, 1997). The six pieces of calcified breccia with a thin veneer of cranial bone have been labelled Sts 5 i–vi. The total surface area of exposed bone measured approximately

Intra-individual metameric variation expressed at the enamel-dentine junction of lower post-canine dentition of South African fossil hominins and modern humans

OBJECTIVES The aim of this study is to compare the degree and patterning of inter- and intra-individual metameric variation in South African australopiths, early Homo and modern humans. Metameric variation likely reflects developmental and taxonomical issues, and could also be used to infer ecological and functional adaptations. However, its patterning along the early hominin postcanine dentition, particularly among South African fossil hominins, remains unexplored. MATERIALS AND METHODS Using microfocus X-ray computed tomography (µXCT) and geometric morphometric tools, we studied the enamel-dentine junction (EDJ) morphology and we investigated the intra- and inter-individual EDJ metameric variation among eight australopiths and two early Homo specimens from South Africa, as well as 32 modern humans. RESULTS Along post-canine dentition, shape changes between metameres represented by relative positions and height of dentine horns, outlines of the EDJ occlusal table are reported in modern and fossil taxa. Comparisons of EDJ mean shapes and multivariate analyses reveal substantial variation in the direction and magnitude of metameric shape changes among taxa, but some common trends can be found. In modern humans, both the direction and magnitude of metameric shape change show increased variability in M2 -M3 compared to M1 -M2 . Fossil specimens are clustered together showing similar magnitudes of shape change. Along M2 -M3 , the lengths of their metameric vectors are not as variable as those of modern humans, but they display considerable variability in the direction of shape change. CONCLUSION The distalward increase of metameric variation along the modern human molar row is consistent with the odontogenetic models of molar row structure (inhibitory cascade model). Though much remains to be tested, the variable trends and magnitudes in metamerism in fossil hominins reported here, together with differences in the scale of shape change between modern humans and fossil hominins may provide valuable information regarding functional morphology and developmental processes in fossil species.