Paranthropus Research Articles

In search of the australopithecines

Evidence from strontium isotope ratios preserved in fossil teeth provides a glimpse into the group dynamics and ranging habits of the australopithecines that can be compared with the patterns for modern primates. See Letter p.76 How do you estimate the home ranges and land-use habits of extinct species? One method is to measure the strontium isotope content of fossil teeth, because strontium isotope ratios are a good indicator of the source of the water that the creature drank during its life. This watermark is determined by the underlying geology. A strontium-isotope study of Australopithecus africanus and Paranthropus robustus specimens from South Africa shows that the smaller individuals, inferred to have been females, ranged further than the males. This suggests that females tended to move away from their natal groups and joined others, whereas males tend to stay at home, a behaviour characteristic of humans and chimpanzees, but not of most gorillas and other primates.

Contemporary flowstone development links early hominin bearing cave deposits in South Africa

The Cradle of Humankind cave sites in South Africa preserve fossil evidence of four early hominin taxa: Australopithecus africanus, Australopithecus sediba, Paranthropus robustus and early Homo. In order to integrate this record into a pan-African scenario of human evolutionary history it is critical to have reliable dates and temporal ranges for the southern African hominins. In the past a lack of precise and accurate chronological data has prevented the evaluation of the temporal relationships between the various sites. Here we report new uranium–lead (U–Pb) radiometric ages obtained from sheets of calcium carbonate flowstone inter-bedded between clastic cave sediments at the site of Swartkrans, providing bracketing ages for the fossiliferous deposits. The fossil bearing units of Swartkrans, specifically the Hanging Remnant and Lower Bank of Member 1, are underlain by flowstone layers dated to 2.25 ± 0.05 Ma and 2.25 ± 0.08 Ma and capped by layers of 1.8 ± 0.01 Ma and 1.7 ± 0.07 Ma. The age bracket of the Member 1 deposits is therefore between 2.31 and 1.64 Ma. However, by combining the U–Pb with biostratigraphic data we suggest that this can be narrowed down to between 1.9 and 1.8 Ma. These data can be compared with other recently dated sites and a radiometrically dated U–Pb age sequence formed: Sterkfontein Member 4, Swartkrans Member 1, Malapa, and Cooper's D. From this new U–Pb dataset, a pattern of contemporary flowstone development emerges, with different caves recording the same flowstone-forming event. Specifically overlapping flowstone formation takes place at Swartkrans and Sterkfontein at ~ 2.29 Ma and ~ 1.77 Ma, and at Sterkfontein and Malapa at ∼ 2.02 Ma. This suggests a regional control over the nature and timing of speleothem development in cave deposits and these flowstone layers could assist in future correlation, both internal to specific deposits and regionally between sites.

Adaptation to hard-object feeding in sea otters and hominins

The large, bunodont postcanine teeth in living sea otters ( Enhydra lutris) have been likened to those of certain fossil hominins, particularly the ’robust’ australopiths (genus Paranthropus). We examine this evolutionary convergence by conducting fracture experiments on extracted molar teeth of sea otters and modern humans ( Homo sapiens) to determine how load-bearing capacity relates to tooth morphology and enamel material properties. In situ optical microscopy and x-ray imaging during simulated occlusal loading reveal the nature of the fracture patterns. Explicit fracture relations are used to analyze the data and to extrapolate the results from humans to earlier hominins. It is shown that the molar teeth of sea otters have considerably thinner enamel than those of humans, making sea otter molars more susceptible to certain kinds of fractures. At the same time, the base diameter of sea otter first molars is larger, diminishing the fracture susceptibility in a compensatory manner. We also conduct nanoindentation tests to map out elastic modulus and hardness of sea otter and human molars through a section thickness, and microindentation tests to measure toughness. We find that while sea otter enamel is just as stiff elastically as human enamel, it is a little softer and tougher. The role of these material factors in the capacity of dentition to resist fracture and deformation is considered. From such comparisons, we argue that early hominin species like Paranthropus most likely consumed hard food objects with substantially higher biting forces than those exerted by modern humans.

Hominin palaeoecology in Late Pliocene Malawi: First insights from isotopes (<sup>13</sup>C, <sup>18</sup>O) in mammal teeth

Carbon-13 and oxygen-18 abundances were measured in large mammal skeletal remains (tooth enamel, dentine and bone) from the Chiwondo Beds in Malawi, which were dated by biostratigraphic correlation to ca. 2.5 million years ago. The biologic isotopic patterns, in particular the difference in carbon-13 abundances between grazers and browsers and the difference in oxygen-18 abundances between semi-aquatic and terrestrial herbivores, were preserved in enamel, but not in dentine and bone. The isotopic results obtained from the skeletal remains from the Chiwondo Beds indicate a dominance of savannah habitats with some trees and shrubs. This environment was more arid than the contemporaneous Ndolanya Beds in Tanzania. The present study confirms that robust australopithecines were able to live in relatively arid environments and were not confined to more mesic environments elsewhere in southern Africa.

Hominin palaeoecology in Late Pliocene Malawi: First insights from isotopes (<sup>13</sup>C, <sup>18</sup>O) in mammal teeth

Carbon-13 and oxygen-18 abundances were measured in large mammal skeletal remains (tooth enamel, dentine and bone) from the Chiwondo Beds in Malawi, which were dated by biostratigraphic correlation to ca. 2.5 million years ago. The biologic isotopic patterns, in particular the difference in carbon-13 abundances between grazers and browsers and the difference in oxygen-18 abundances between semi-aquatic and terrestrial herbivores, were preserved in enamel, but not in dentine and bone. The isotopic results obtained from the skeletal remains from the Chiwondo Beds indicate a dominance of savannah habitats with some trees and shrubs. This environment was more arid than the contemporaneous Ndolanya Beds in Tanzania. The present study confirms that robust australopithecines were able to live in relatively arid environments and were not confined to more mesic environments elsewhere in southern Africa.

Niche Construction through Cooperation: A Nonlinear Dynamics Contribution to Modeling Facets of the Evolutionary History in the GenusHomo

The transition from early members of the genus Homo to Homo erectus/ergaster is marked by subtle morphological shifts but resulted in substantial changes in evolutionary trajectory. Predation pressures on the hominins may have been significant in influencing this transition. These contexts might have stimulated a shift in behavior and modes of engagement with the environment that initiated a complex suite of changes facilitating the emergence of current features of humanity. In this report we outline a potential model for these shifts based on nonlinear dynamical interactions involving niche construction and increased reliance on complex cooperation as an antipredator strategy. Modeling proposed selective predation pressures on early humans, leading to the idea that increasingly complex sociality, patterns of cooperation, and niche construction laid the foundation for the successful emergence and spread of the genus Homo and potentially a concomitant decline for the genus Paranthropus.

Early hominin dental remains from the Plio-Pleistocene site of Drimolen, South Africa

The Plio-Pleistocene fossil hominin site of Drimolen is located approximately 5.5 km north of the other well-known South African Plio-Pleistocene sites (Sterkfontein, Swartkrans, Kromdraai, Coopers). It was discovered by A.W. Keyser in 1992. Systematic excavations led to the recovery of a remarkable number of fossil vertebrate taxa, including hominins. Most of the specimens collected consist of isolated teeth or those in jaws. The aim of this paper is to provide a morphological description of the dental specimens. The taxonomic allocation of each specimen is also reported, either confirming or revising previous provisional attributions. The analysis confirms the occurrence of two hominin species, Paranthropus robustus and Homo sp. With over 80 fossil hominin specimens recovered so far, Drimolen is the second largest sample of P. robustus, after Swartkrans. At Drimolen, P. robustus is represented mostly by craniodental specimens (63) among which are 47 isolated teeth and the remainder are maxillary and mandibular fragments with teeth. The assemblage markedly increases the dental sample of P. robustus. Furthermore, the Drimolen sample includes tooth classes not present in the Swartkrans or Kromdraai samples. The new tooth classes include both deciduous upper lateral incisors (DNH 31) and canines (DNH 23). In the dental sample described here there are nine specimens probably attributable to Homo, although a specific attribution is not yet possible. These specimens expand the small sample of early Homo from South African sites. Basic dimensions (MD and BL) of the Drimolen dental remains are compared in a preliminary analysis with other hominin samples. This analysis delineates the Drimolen P. robustus dental sample as characterized by smaller teeth overall than the Swartkrans sample (and in some cases also smaller than the Kromdraai sample), as well as a greater size range.

One or two species? A morphometric comparison between robust australopithecines from Kromdraai and Swartkrans

The type specimen of Paranthropus robustus (TM 1517, including a partial cranium) was discovered at Kromdraai near Sterkfontein in 1938 and described by Robert Broom as a new species. Subsequently, more robust australopithecines were discovered at the nearby site of Swartkrans. These Swartkrans hominins were described by Broom as Paranthropus crassidens. Many palaeoanthropologists currently regard the robust australopithecines from Kromdraai and Swartkrans as one species, but consensus has not been reached on this issue. A morphometric analysis has been undertaken to assess the probability that specimens attributed to P. crassidens represent the same species as that which is represented by TM 1517, the holotype of P. robustus. Our results failed to reject the null hypothesis that both sites sample the same, single species of robust australopithecine.

The Effect of Early Hominin Occlusal Morphology on the Fracturing of Hard Food Items

Tooth profile plays an important role in interpretations of the functional morphology of extinct species. We tested hypotheses that australopith occlusal morphology influences the fracture force required to crack large, hard food items using a combination of physical testing and finite element analysis (FEA). We performed mechanical experiments simulating both molar and premolar biting using metal replicas of four hominin specimens representing species that differ in occlusal relief (Praeanthropus afarensis, Australopithecus africanus, Paranthropus robustus, and P. boisei). The replicas were inserted into an Instron machine and used to fracture hollow acrylic hemispheres with known material properties. These hemispheres simulate a hard and brittle food item but exhibit far less variability in size and strength than actual nuts or seeds, thereby facilitating interpretations of tooth function. Fracture forces and fracture displacements were measured, and analysis of variance revealed significant differences in fracture force and energy between specimens and tooth types. Complementing the physical testing, a nonlinear contact finite element model was developed to simulate each physical test. Experimental and FEA results showed good correspondence in most cases, and FEA identified stress concentrations consistent with mechanical models predicting that radial/median fractures are important factors in the failure of nut and seed shells. The fracture force data revealed functional similarities between relatively unworn Pr. afarensis and P. robustus teeth, and between relatively unworn A. africanus and heavily worn P. boisei teeth. These results are inconsistent with functional hypotheses, and raise the possibility that the tooth morphology of early hominins and other hard object feeders may not represent adaptations for inducing fractures in large, hard food items, but rather for resisting fractures in the tooth crown.

Body size and body shape in early hominins – implications of the Gona Pelvis

Discovery of the first complete Early Pleistocene hominin pelvis, Gona BSN49/P27, attributed to Homo erectus, raises a number of issues regarding early hominin body size and shape variation. Here, acetabular breadth, femoral head breadth, and body mass calculated from femoral head breadth are compared in 37 early hominin (6.0–0.26 Ma) specimens, including BSN49/P27. Acetabular and estimated femoral head sizes in the Gona specimen fall close to the means for non- Homo specimens ( Orrorin tugenesis, Australopithecus africanus, Paranthropus robustus), and well below the ranges of all previously described Early and Middle Pleistocene Homo specimens. The Gona specimen has an estimated body mass of 33.2 kg, close to the mean for the non- Homo sample (34.1 kg, range 24–51.5 kg, n = 19) and far outside the range for any previously known Homo specimen (mean = 70.5 kg; range 52–82 kg, n = 17). Inclusion of the Gona specimen within H. erectus increases inferred sexual dimorphism in body mass in this taxon to a level greater than that observed here for any other hominin taxon, and increases variation in body mass within H. erectus females to a level much greater than that observed for any living primate species. This raises questions regarding the taxonomic attribution of the Gona specimen. When considered within the context of overall variation in body breadth among early hominins, the mediolaterally very wide Gona pelvis fits within the distribution of other lower latitude Early and Middle Pleistocene specimens, and below that of higher latitude specimens. Thus, ecogeographic variation in body breadth was present among earlier hominins as it is in living humans. The increased M-L pelvic breadth in all earlier hominins relative to modern humans is related to an increase in ellipticity of the birth canal, possibly as a result of a non-rotational birth mechanism that was common to both australopithecines and archaic Homo.

The human lineage

The human lineage

Dietary adaptations of South African australopiths: inference from enamel prism attitude

The angle at which enamel prisms approach the wear surface holds information with regard to the stiffness of the tissue, as well as its wear resistance. Hence, analyses of prism orientation may shed light on questions of whether the thick enamel in hominins has evolved to confer stiffness or wear resistance to the teeth and may thus inform about the diet and behavioural ecology of these species. This was explored for Paranthropus robustus and Australopithecus africanus, whereby a distinction was made between prisms at the Phase I and Phase II facets. The results were compared with those obtained for Theropithecus, Macaca, and Potamochoerus for whom behavioural and/or experimental data are available, and were interpreted against simple mechanical principles. The South African hominins differ significantly in their relationships between wear facets and prism angulations. Teeth of P. robustus are better adapted to more vertical loads during mastication (Phase I), whereas those of A. africanus are better adapted to cope with more laterally-directed loads (Phase II) commonly associated with roll-crush and mastication. Overall, teeth of P. robustus appear stiffer, while those of A. africanus seem more wear resistant.

New Australopithecus robustus fossils and associated U-Pb dates from Cooper's Cave (Gauteng, South Africa)

Australopithecus robustus is one of the best represented hominin taxa in Africa, with hundreds of specimens recovered from six fossil localities in the Bloubank Valley area of Gauteng Province, South Africa. However, precise geochronological ages are presently lacking for these fossil cave infills. In this paper, we provide a detailed geological background to a series of hominin fossils retrieved from the newly investigated deposit of Cooper's D (located partway between Sterkfontein and Kromdraai in the Bloubank Valley), including uranium-lead (U-Pb) ages for speleothem material associated with A. robustus. U-Pb dating of a basal speleothem underlying the entire deposit results in a maximum age of 1.526 (±0.088) Ma for Cooper's D. A second U-Pb date of ca. 1.4 Ma is produced from a flowstone layer above this basal speleothem; since this upper flowstone is not a capping flowstone, and fossiliferous sediments are preserved above this layer, some of the hominins might be slightly younger than the calculated age. As a result, we can broadly constrain the age of the hominins from Cooper's D to between 1.5 and approximately 1.4 Ma. Extinct fauna recorded in this comparatively young deposit raise the possibility that the Bloubank Valley region of South Africa represented a more stable environmental refugium for taxa relative to tectonically more active East Africa. The sediments of the deposit likely infilled rapidly during periods when arid conditions prevailed in the paleoenvironment, although it is unclear whether sediment deposition and bone deposition were necessarily contemporaneous occurrences. We reconstruct the paleoenvironment of Cooper's D as predominantly grassland, with nearby woodlands and a permanent water source. The hominin teeth recovered from Cooper's D are all from juveniles and can be confidently assigned to A. robustus. In addition, two juvenile mandibular fragments and an adult thoracic vertebra are tentatively attributed to A. robustus.

Assessing the function of early hominin bone tools

Bone tools from early hominin sites in southern Africa continue to intrigue researchers interested in the development of early human technology and cognition. Sterkfontein, Swartkrans and Drimolen have all yielded bone tools dated to between 1 and 2 Mya associated with numerous Paranthropus robustus and few early Homo remains. The bone tools are described by different authors as implements used to excavate tubers from the ground and termites from their nests, work hides and strip bark from trees. The purpose of this research was to develop a more powerful analytical tool for the study and interpretation of bone surface modifications in general, and early hominin bone tool function(s) in particular. We used an optical interferometer to scan the worn areas of a sample of bone tools from Swartkrans and Drimolen, an ethnographic collection of implements used for defleshing marula fruits, and a set used experimentally to excavate in the ground and in termite mounds. The 3D rendering of archaeological and experimental wear patterns better highlights previously described differences between these patterns, and demonstrates the pertinence of this analytical tool to visually discriminating between different bone modifications. Analysis of selected 2D and 3D roughness variables indicates that the wear pattern on the early hominin bone tools from Drimolen is significantly different from that of tuber digging, very similar to termite foraging, and not unlike marula fruit processing. Marked differences are detected between the Swartkrans and Drimolen wear patterns, which suggests that the tools from these sites may have been used with different motions, in contact with abrasive particles of different size, or in different tasks. Principal component analyses conducted on 2D and 3D variables suggest that early hominin bone tools from southern Africa may have been used to forage for termites, extract tubers in a motion parallel to the tool main axis, process fruits and conduct other, as yet unidentified, tasks.

Protostylid expression at the enamel-dentine junction and enamel surface of mandibular molars of Paranthropus robustus and Australopithecus africanus

Distinctive expressions and incidences of discrete dental traits at the outer enamel surface (OES) contribute to the diagnoses of many early hominin taxa. Examination of the enamel-dentine junction (EDJ), imaged non-destructively using micro-computed tomography, has elucidated the morphological development of dental traits and improved interpretations of their variability within and among taxa. The OES expressions of one of these dental traits, the protostylid, have been found to differ among African Plio-Pleistocene fossil hominin taxa. In this study protostylid expression is examined at the OES and at the EDJ of Paranthropus robustus ( n = 23) and Australopithecus africanus ( n = 28) mandibular molars, with the goals of incorporating EDJ morphology into the definition of the protostylid and assessing the relative contribution of the EDJ and enamel cap to its expression in these taxa. The results provide evidence a) of statistically significant taxon-specific patterns of protostylid morphology at the EDJ that are not evident at the OES; b) that in P. robustus, thick enamel reduces the morphological correspondence between the form of the protostylid seen at the EDJ and the OES, and c) that if EDJ images can be obtained, then the protostylid retains its taxonomic value even in worn teeth.

Indications of habitat association of Australopithecus robustus in the Bloubank Valley, South Africa

Establishing the habitat preferences of early hominin taxa is a necessary, though difficult, requirement for understanding the interaction between environmental change and hominin evolution. The environments typically associated with Australopithecus robustus have been reconstructed as predominantly open grasslands situated within a habitat mosaic that included a more wooded component with a nearby perennial water source. Most studies have concluded that the open grassland component represents the habitat preference of the hominins. In this study we investigate indicators of habitat association of A. robustus that are preserved in the animal paleocommunities represented in a series of fossil cave infills in the Bloubank Valley of South Africa, including Swartkrans, Sterkfontein, Kromdraai, and Coopers. Testing for conditions of isotaphonomy reveals a potential bias relating to depositional matrix and perhaps accumulating agent, though such a bias has not unduly influenced the taxonomic composition the assemblages. Correspondence analysis of census data from modern African nature reserves demonstrates that carnivore predation patterns are indicative of animal communities, which in turn are representative of habitats. As a result, modern census data are used to document patterns of habitat preference of large herbivores, thus allowing assignment of fossil taxa to a series of broadly defined habitat categories. Correspondence analysis of fossil assemblages reveals that the abundance profile of A. robustus is most similar to that of woodland-adapted taxa. In addition, fluctuations in the relative abundance of taxa assigned to the broad habitat categories reveal a significant negative correlation between A. robustus and open grassland-adapted taxa, indicating that the more grassland-adapted taxa there are in a given assemblage, the fewer hominins there tend to be. Thus, it appears that the open grasslands that comprise the majority of the paleoenvironments associated with A. robustus do not necessarily indicate the habitat preference of the hominins. Rather, it would appear that in addition to being dietary generalists, A. robustus were also likely to have been habitat generalists.

Enamel-dentine junction (EDJ) morphology distinguishes the lower molars of Australopithecus africanus and Paranthropus robustus

Tooth crown morphology plays a central role in hominin systematics, but the removal of the original outer enamel surface by dental attrition often eliminates from consideration the type of detailed crown morphology that has been shown to discriminate among hominin taxa. This reduces the size of samples available for study. The enamel-dentine junction (EDJ) is the developmental precursor and primary contributor to the morphology of the unworn outer enamel surface, and its morphology is only affected after considerable attrition. In this paper, we explore whether the form of the EDJ can be used to distinguish between the mandibular molars of two southern African fossil hominins: Paranthropus (or Australopithecus) robustus and Australopithecus africanus. After micro-computed tomographic scanning the molar sample, we made high-resolution images of the EDJ and used geometric morphometrics to compare EDJ shape differences between species, in addition to documenting metameric variation along the molar row within each species. Landmarks were collected along the marginal ridge that runs between adjacent dentine horns and around the circumference of the cervix. Our results suggest that the morphology of the EDJ can distinguish lower molars of these southern African hominins, and it can discriminate first, second, and third molars within each taxon. These results confirm previous findings that the EDJ preserves taxonomically valuable shape information in worn teeth. Mean differences in EDJ shape, in particular dentine horn height, crown height, and cervix shape, are more marked between adjacent molars within each taxon than for the same molar between the two taxa.

Mechanical Properties of Plant Underground Storage Organs and Implications for Dietary Models of Early Hominins

The diet of early human ancestors has received renewed theoretical interest since the discovery of elevated δ13C values in the enamel of Australopithecus africanus and Paranthropus robustus. As a result, the hominin diet is hypothesized to have included C4 grass or the tissues of animals which themselves consumed C4 grass. On mechanical grounds, such a diet is incompatible with the dental morphology and dental microwear of early hominins. Most inferences, particularly for Paranthropus, favor a diet of hard or mechanically resistant foods. This discrepancy has invigorated the longstanding hypothesis that hominins consumed plant underground storage organs (USOs). Plant USOs are attractive candidate foods because many bulbous grasses and cormous sedges use C4 photosynthesis. Yet mechanical data for USOs—or any putative hominin food—are scarcely known. To fill this empirical void we measured the mechanical properties of USOs from 98 plant species from across sub-Saharan Africa. We found that rhizomes were the most resistant to deformation and fracture, followed by tubers, corms, and bulbs. An important result of this study is that corms exhibited low toughness values (mean = 265.0 J m−2) and relatively high Young’s modulus values (mean = 4.9 MPa). This combination of properties fits many descriptions of the hominin diet as consisting of hard-brittle objects. When compared to corms, bulbs are tougher (mean = 325.0 J m−2) and less stiff (mean = 2.5 MPa). Again, this combination of traits resembles dietary inferences, especially for Australopithecus, which is predicted to have consumed soft-tough foods. Lastly, we observed the roasting behavior of Hadza hunter-gatherers and measured the effects of roasting on the toughness on undomesticated tubers. Our results support assumptions that roasting lessens the work of mastication, and, by inference, the cost of digestion. Together these findings provide the first mechanical basis for discussing the adaptive advantages of roasting tubers and the plausibility of USOs in the diet of early hominins.

Early hominid bone tools from Drimolen, South Africa

The earliest use of bone tools is a topic of ongoing debate that concerns the criteria used to identify utilised or minimally modified bone tools, and if verified, the implications for hominid adaptation and cognition. Here we present the first description of 22 possible bone tools from the early hominid site of Drimolen (Gauteng Province, South Africa), dated ∼1.5–2 Mya. We compare the results of a taphonomic, morphometric and microscopic analysis of these pieces with those obtained from the study of faunal assemblages modified by a variety of non-human agents, and experimentally modified bones. None of the naturally modified assemblages contained pieces bearing the wear pattern observed on specimens from Drimolen and on bones experimentally used in digging activities. Fourteen pieces from Drimolen bear a pattern comparable to one previously described on early hominid bone tools from Sterkfontein and Swartkrans. This suggests that Drimolen bone tools were involved in a similar, if not exactly the same, task. Other common features include favoured bone types, fracture patterns, and the length and position of the worn area. Larger bone tools known from Swartkrans are absent at Drimolen, perhaps due to less availability of large mammal bones. The association of a high number of Paranthropus remains with bone tools at Drimolen, and the exceedingly low number of stone tools at the site supports the hypothesis that Paranthropus robustus used these bone tools. Based on implement-assisted termite foraging strategies amongst chimpanzees, we have inferred similar social and cultural behaviours for early hominids. Gorillas were recently proposed as a model for P. robustus social structure due to the high degree of sexual dimorphism observed. According to female aggregation practices present in both models, one can speculate that if P. robustus was the user of the bone tools, the foraging activity in which they were used may have been conducted mainly by females.

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.