The probability of finding an ancestor’s fossil horizon that is at least 0.8 Ma younger than the descendant’s is, by definition, zero when temporal range overlap is less than or equal to 0.8 Ma (Figs. 2A and 3 and Eq. 5c). This probability monotonically increases with range overlap when overlap is greater than 0.8 Ma (Fig. 3 and Eq. 5c) for reasons discussed above (Fig. 2A). However, even when the two species’ ranges completely overlap, which is impossible for ancestor-descendant species and is only presented as a theoretical upper bound, the computed P value is only 0.016 (Fig. 3 and Eq. 5c). If we treat all possible values of range overlap as equally likely, the mean P value over all overlap values is 0.0009 (Eq. 6c). We have confirmed our probability model results with simulations (fig. S1 and data file S5).
Fig. 3 Probability of finding an ancestor’s fossil horizon that is at least 0.8 Ma younger than the descendant’s fossil horizon (P value).
Reviewing the paleoanthropology literature, we recorded 28 hypothesized ancestor-descendant species pairs (table S1). There is only one instance where an ancestor’s first-discovered fossil postdated the descendant’s: ancestor Homo erectus sensu lato (Kedung Brubus 1) dated to 0.8 to 0.7 Ma ago (12) and descendant Homo antecessor (ATD6-1) dated to 0.9 to 0.8 Ma ago (13). The age difference between these specimens (i.e., 0.1 Ma) is far less than the age difference observed between A. sediba and earliest Homo (i.e., 0.8 Ma) (Fig. 4). When the mean and SD of the 28 observed age differences are used to generate a normal distribution model (bell curve in Fig. 4), 0.8 Ma falls in the >99.9th percentile, which translates to a P value less than 0.001.
Fig. 4 Histogram of the geological age differences between first-discovered fossils in purported hominin ancestor-descendant species pairs (n = 28).
We can explore how strongly our assumptions influenced our modeling results. We calculated our P values, assuming the 2.8-Ma-old Ledi-Geraru mandible actually belongs to Homo (5). Some researchers dispute this (14), so we also ran our analyses assuming A.L. 666-1 (2.33 Ma-old)—a specimen widely regarded as Homo—represents the oldest Homo specimen (15). Although a handful of researchers argue that all pre–1.9-Ma-old specimens assigned to Homo are invalidly named or are poorly dated (2, 3), we view this assertion as unlikely [as does Robinson et al. (6)]. By selecting a younger fossil to represent the oldest Homo specimen, we are decreasing the observed age difference between A. sediba and earliest Homo, which should increase the P values overall (Eq. 5c). We also explored whether our choice of 0.97 Ma to represent hominin temporal durations might affect our results because using a longer duration will increase the amount of time associated with a given percentage of range overlap between two species, and this should increase P values as well (Eq. 5c). We therefore reran our analyses assuming hominin temporal durations of 2 Ma, which is at the larger end of estimated mean species durations in African large mammals [all African large mammals: 2.3 Ma (16); eastern African bovids: 1.4 Ma (17); large mammals in the Omo-Turkana Basin, Ethiopia/Kenya: 1.4 Ma (17); Australopithecus anamensis-afarensis: 1.2 Ma (7, 8)]. Results show that calculated P values are still small even when relaxing the age of earliest Homo to 2.33 Ma ago or hominin temporal durations to 2 Ma. For example, P values exceed 0.05 only when range overlap is at least 70%, and the mean and maximum P values over all possible overlap values are only 0.04 and 0.20, respectively (Eqs. 5c and 6c, and fig. S2, A and B). When both assumptions are simultaneously relaxed, P values exceed 0.05 when overlap is at least 50%, and the mean and maximum P values are 0.093 and 0.34, respectively (Eqs. 5c and 6c, and fig. S2C).
For our model, we assumed that the probability of recovering a fossil horizon from each of the A. sediba and earliest Homo temporal ranges is uniform through time. This assumption is a parsimonious one given that only one horizon each has been sampled from A. sediba (1, 2) and earliest Homo (5), and a uniform fossil recovery potential (FRP) (i.e., the probability of finding a fossil horizon) is a good approximation for the one hominin lineage where FRP has been explored, i.e., A. anamensis-afarensis (7, 8). However, we also have to consider the possibility that FRP is not uniform through time in the A. sediba and earliest Homo temporal ranges. Our P values would only be biased downward if FRP is greater in South Africa and eastern Africa during the geological time periods when A. sediba and earliest Homo are found, respectively. This is because if FRP is actually higher toward the end and beginning of the A. sediba and earliest Homo temporal ranges, respectively, then it is more likely that one will recover an A. sediba horizon that is much younger than an earliest Homo horizon, even if the former species is ancestral to the latter. Using the number of hominin fossil horizons—defined as midpoint ages of hominin-bearing members with age duplicates removed (see data file S3) (7, 8)—as a proxy for FRP, we find that FRP is not appreciably higher during the times when A. sediba and earliest Homo are found in their respective geographic regions (fig. S3). There is the possibility that FRP might be slightly higher in South Africa around the time of A. sediba (fig. S3), but even if we double the probability of recovering a fossil horizon in the last 25% of the ancestor’s (i.e., A. sediba) temporal range, the maximum P value is only 0.025 (fig. S4).
The issue of the origin of Homo is one of the thorniest questions in paleoanthropology and one that has led to myriad proposals and, sometimes, speculations (2, 3, 18, 19). Answers to the questions of how, when, and where the earliest representatives of the genus emerged are still in flux, owing especially to the dearth of fossil data from the relevant temporal range (3.0 to 2.5 Ma ago). It is therefore important to use all available lines of evidence when addressing a question as data poor as this one. While fossil remains from the 3.0- to 2.5-Ma-old interval are necessary to reasonably document the morphological patterns surrounding the origin of Homo, probabilistic methods such as the one used here are also critical for assessing the chronological evidence for proposed relationships between Homo and candidate ancestors. Hypothesized ancestor-descendant relationships must satisfy both temporal and morphological criteria (7, 20). We tested the first criterion here, and the second one has been tested elsewhere (11). A. sediba fails both benchmarks, and the most viable ancestral candidate for the genus Homo remains Australopithecus afarensis both on morphological (5) and temporal grounds (7, 8).
Science Advances 08 May 2019: Vol. 5, no. 5, eaav9038
Our results show that the facial skeleton of A. sediba specimen MH1 was strong relative to that of A. africanus specimen Sts 5 even though the former lacks many of the derived facial buttressing features seen in other australopiths. With a few exceptions, strain magnitudes from homologous locations on the FEMs were lower in the A. sediba model than in the A. africanus model during both premolar and molar biting (Figs 1 and 2). Nearly, all regions we examined experienced lower strain magnitudes in A. sediba for all forms of strain during both premolar (Supplementary Table 1) and molar (Supplementary Table 2) biting. The only exceptions to this are that A. sediba exhibited slightly higher maximum principal (tensile) strain in the balancing-side zygomatic root during both premolar and molar biting. The magnitude of minimum principal (compressive) strain was greater in the balancing dorsal orbital, working infraorbital and working zygomatic body regions of MH1, for both bites. There was also somewhat higher maximum shear strain in the working infraorbital during premolar biting, and somewhat higher shear and von Mises strain in the balancing dorsal orbital of MH1. However, for the infraorbital region, A. africanus exhibits a region of high strain just medial to where the working infraorbital strain was collected that extends from the inferior orbital rim to the root of the zygomatic. This is likely related to the more curved zygomaticoalveolar crest of Sts 5 combined with its more laterally flaring zygoma. Strain energy density in the balancing dorsal orbitals of A. sediba and A. africanus were identical. Strain mode also differed slightly between the models. Strain mode for the working postorbital bar was somewhat more compressive in A. sediba during premolar biting, as opposed to being tensile in A. africanus. In addition, the balancing mid-zygomatic arch of A. sediba was tensed slightly more than it was compressed during both premolar and molar biting, while compression was dominant in the arch of A. africanus.
Figure 1: Line plot of von Mises strain generated during simulated biting in finite element models.
Although Sts 5 experiences systematically higher strain magnitudes than MH1, the extent of the differences between these two hominins does not exceed that observed among a sample of chimpanzees that differ notably in shape (Fig. 1); strains in Sts 5 are often towards the high end or middle of the chimpanzee range, while those in MH1 are consistently toward the bottom of or below that range. Thus, although one can conclude that MH1 is strong relative to the other crania, more work is needed to determine whether or not that strength reflects a species-level property differentiating A. sediba from chimpanzees and A. africanus.
Figure 2: Colour mapping of von Mises strain in finite element models of Sts 5 (A. africanus) and MH1 (A. sediba) crania during simulated left premolar (P3) and left molar (M2) biting (not to scale).
Although Sts 5 experiences systematically higher strain magnitudes than MH1, the extent of the differences between these two hominins does not exceed that observed among a sample of chimpanzees that differ notably in shape (Fig. 1); strains in Sts 5 are often towards the high end or middle of the chimpanzee range, while those in MH1 are consistently toward the bottom of or below that range. Thus, although one can conclude that MH1 is strong relative to the other crania, more work is needed to determine whether or not that strength reflects a species-level property differentiating A. sediba from chimpanzees and A. africanus.
Figure 3: Ontogenetic changes among the dentition, malar root and temporomandibular joint in 319 extant African apes and humans.
These results have not been biased by the subadult age of MH1. Previous studies have demonstrated in apes19, monkeys20 and other hominins19,21,22,23,24 that developmental changes in overall cranial morphology that occur subsequent to first molar eruption produce relatively minor variations in shape relative to the changes that occur earlier in ontogeny. Moreover, one study in Old World monkeys has shown that many (although not all) components of the masticatory system exhibit consistent spatial relationships with each other during growth from juvenile stages to adulthood25. Our geometric morphometric analysis of ontogenetic change in African apes and humans suggests that the important functional relationships in MH1 among the dentition, malar root and temporomandibular joint (TMJ) would likewise have not changed markedly during the later stages of development. These are key landmarks to consider because collectively they affect the relative positioning of critical components of the biomechanical system, namely, the point of loading (that is, the bite point), some of the applied external forces (that is, the masseter muscle) and the fulcrum (TMJ). If, for example, the positions of the tooth row relative to the zygomatic root and TMJ were markedly different in adults compared with juveniles of the age of MH1, then results derived from MH1 might have limited utility in characterizing the mechanics of the species. However, relative to African ape juveniles lacking permanent teeth, those individuals with the second molar in occlusion have nearly achieved the adult configuration in these features (Fig. 3a). And, while subsequent ontogenetic changes are measurable, they do not substantially alter the arrangement of the masticatory apparatus (Fig. 3b). In other words, even if MH1 had lived to grow along the ontogenetic trajectory of an extant ape, the resulting adult form would have been very similar to that preserved in the existing fossil with respect to the morphological features under consideration. Moreover, even though A. sediba is represented in this study by a single individual, prior work on chimpanzee crania has shown that mechanical variation within species is conservative even when intraspecific shape variation is high26. Thus, even though it is always desirable to examine more specimens (particularly in fossil taxa), there is reason to believe that these results are broadly applicable to the species as a whole, with the caveat that mechanical variation at approximately the level seen in chimpanzees might be expected.
Constraints On balance, one might conclude that the cranium of MH1 is well configured to consume hard foods, insofar as its facial skeleton is structurally strong (notwithstanding sampling limitations) and it appears to produce bite force efficiently. However, there is an important constraint on bite force production that argues against this interpretation. In this ‘constrained lever’ model27,28 (Fig. 4), it is assumed that the two TMJs are loaded in compression (in which the mandibular condyles are drawn into the joints). This will occur when the vector resultant of all of the masticatory muscle forces passes through a ‘triangle of support’ defined by the bite point and the two TMJs. If, however, the muscle resultant were to fall outside of the triangle of support, then the working (biting) side TMJ would experience a distractive reaction force in which the condyle is ‘pulled’ out of the joint. The soft tissues of the TMJ are poorly configured to resist distractive joint forces, and thus could be damaged if the joint were to dislocate in this manner.
Figure 4: The constrained lever model of jaw biomechanics.
The muscle resultant will fall in the midline (that is, the midsagittal plane) when the muscles of mastication are acting with bilateral symmetry (equal forces on both sides)27,28. As a generalization, such a midline muscle resultant passes through the triangle of support during bites on the mesial teeth (that is, incisors, canines and premolars). Thus, the model27 does not predict distraction during bites on such teeth. However, as the bite point moves distally on the tooth row towards the molars, the shape of the triangle of support changes such that a midline muscle resultant may lie outside of the triangle (Fig. 4), and thus create a distractive joint force. To bring the resultant within the triangle, one can reduce the activity levels of the balancing (non-biting) side muscles27,28. This has the effect of moving the muscle resultant towards the working side and back within the triangle (Fig. 4). In such bites, there is an asymmetry in the activity levels of the working and balancing-side muscles, a consequence of which is that overall muscle force is reduced. Thus, although one might expect that a bite on a distal tooth might produce an elevated bite force, this expectation is mitigated by the constraint that muscle force may be reduced during such a bite to prevent joint distraction. In theory, there is an alternative means of moving the muscle resultant into the triangle of support, namely, by reducing the anterior-most fibres of each muscle so as to move the muscle resultant posteriorly. This is difficult to model but, regardless, the effect on bite force is the same: reduced muscle forces necessarily imply reduced bite forces.
Taxa in which the molar teeth are positioned antero-posteriorly close to the TMJs (that is, as in a species with a retracted face) are especially at risk of having a midline muscle resultant fall outside of the triangle of support and this problem is exacerbated if those taxa also have masticatory muscles that are positioned anteriorly28. Thus, it is a paradox that a feeding apparatus configured precisely in a way that increases mechanical advantage (that is, by increasing the leverage of the chewing muscles while simultaneously reducing the load arm of the bite point) is also subject to a constraint requiring a reduction in balancing-side muscle force that limits bite force production. The molar teeth in A. sediba are positioned relatively close to the TMJs13, and the origin of the masseter muscle is positioned towards the mesial end (rather than the middle) of the molar row (Fig. 5). Thus, one might expect that A. sediba was at risk of experiencing distractive joint forces during molar biting.
Figure 5: Orientation of the joint reaction force at the working (biting) side temporomandibular joint (TMJ) in models of (MH1) (A. sediba) and Sts 5 (A. africanus) during simulated left premolar (P3) and left molar (M2) biting.
In our FEA simulations, the TMJs on the working (biting) sides of both the Sts 5 and MH1 crania experience compressive reaction forces during premolar biting, as predicted by biomechanical models27,28. This indicates that the jaw adductor muscle resultant vector passed safely through the triangle of support. Sts 5 similarly exhibits a faintly compressive reaction force during molar biting, which is consistent with the hypothesis that anthropoid primates may be buffered against TMJ distraction as muscle activity levels vary dynamically during molar mastication28. However, the working-side TMJ of the MH1 cranium experiences a distractive reaction force during maximal molar biting (Fig. 5; Table 1). Only one of the six chimpanzee models experiences a distractive TMJ force29, and in that individual the absolute value of the distractive force was an order of magnitude less than that recorded in MH1. Mammals avoid distractive TMJ reaction forces by reducing the activity levels of the chewing muscles on the balancing (non-biting) side of the skull27,28. The exact pattern by which they do this is difficult to predict, but it was found that when the balancing-side muscle forces in MH1 were all equally reduced by nearly 30%, then the MH1 model produced a working-side joint reaction force during molar biting that was not distractive (Table 1), and that had an orientation similar to that of Sts 5. This reduction in muscle forces in MH1 resulted in a maximum bite force that was reduced by ∼15%. We expect that in life, both A. africanus and A. sediba would have exhibited further reductions in balancing-side muscle force to maintain a safety factor to avoid dislocating the working-side TMJ28, as has been observed in modern humans30. Indeed, the nearly 30% value falls comfortably within the dispersion of experimental values observed during biting on the distal-most molar in modern humans30, who can exhibit even a 50% reduction (note that in MH1, the second molar is its distal-most tooth owing to its subadult age). Because scaled chimpanzee muscle forces are only a coarse proxy for muscle forces in the model of MH1, it is possible that differences in muscle size and/or force ratios could impact the results for the TMJ reaction forces, and potentially the conclusions relating to constraints on feeding biomechanics in A. sediba. To examine this further, we ran the premolar and molar biting simulations in MH1 a third time, using the muscle forces of another closely related species, Homo sapiens. Using these forces, it was found that balancing-side muscle force reductions necessary to eliminate distraction at the working side were only half those needed when using chimpanzee forces (Supplementary Table 3). Nonetheless, it is clear that the potential for muscle recruitment is more limited in MH1 than in Sts 5, and that the feeding apparatus in MH1 is not well buffered against TMJ distraction during molar chewing. Although MH1 would likely have been able to produce bite forces high enough to fracture some hard foods, our simulation suggests that the cranium of this specimen is not optimized to produce high bite force on the molars. Moreover, while MH1 could have efficiently produced bite force on the premolars, the presence of small premolar teeth in the conspecific specimen MH2 argues against the likelihood that premolar loading of hard foods with a high bite force was a significant behavior in A. sediba because the size of a tooth limits its maximum strength31. Thus, if these specimens are broadly representative of the species, our results do not support a hypothesis that A. sediba was adapted to eat hard foods. Previous analyses of carbon isotopes and dental calculus reveal that MH1 may have had a varied diet consisting of the tissues (including bark) of a range of plants utilizing the C3 photosynthetic pathway7. Our findings are consistent with this hypothesis, but suggest that hard-object feeding may not have been a behaviour that drove craniofacial evolution in A. sediba.
The phylogenetic relationships of A. sediba are a topic of debate. It has been hypothesized that A. sediba lies near the ancestry of Homo or is otherwise a close phylogenetic relative of the Homo clade13, but it has also been asserted that A. sediba is instead a phyletic descendant of A. africanus lacking especially close affinities to Homo14. Under both scenarios, our study has similar implications for the origin of Homo. If A. sediba and Homo are closely related, and if specimens drawn from the base of the Homo radiation exhibit limitations on molar bite force production similar to that found in A. sediba (as would be likely in Homo specimens exhibiting facial retraction), then it is reasonable to infer that these shared biomechanical constraints (caused especially by a short horizontal distance between the molar teeth and the TMJs) and their attendant behavioural limitations characterize the ancestors of our genus. These ancestors were almost certainly descended from gracile australopiths, for example, refs 13, 33, 34, 35, 36, 37, 38, who had adaptations for feeding on mechanically resistant foods, for example, refs 8, 9, 10, 29, 39, 40. In this scenario, we hypothesize that environmental change in the late Pliocene and/or early Pleistocene41,42,43 disrupted the ecological niches of gracile australopiths necessitating changes in dietary ecology. One clade of descendants accentuated adaptations for eating mechanically resistant foods for example, ref. 29, and evolved into the robust australopiths of the genus Paranthropus. Another clade (including A. sediba) seemingly abandoned the ability to process such foods orally and one lineage within this clade evolved into Homo. Large brains evidently do not characterize all members of this clade (for example, MH1), so the onset of this evolutionary trajectory may have preceded the evolution of brain expansion that so markedly characterizes our genus.
Professor Rogers first set out to see if the currently-known episodes of interbreeding were enough to explain the distribution of genes among the four populations.
They found that alone they were not, but that adding a single extra episode of interbreeding around 700,000 years ago, involving a shared ancestor of both Denisovans and Neanderthals, was enough to make sense out of the data.
This shared ancestor came from after the split with the human branch of the hominin family tree and is believed to have bred with a mystery population of 'super-archaic' hominins — the same one that the Denisovans would later mate with.
The first hominin species to migrate out into other continents was likely Homo erectus, which emerged from Africa around 2 million years ago and had migrated eastwards to reach Dmanisi in Georgia about 1.8 million years ago.
H. erectus ultimately migrated at least as far as Indonesia, where it is thought they survived until around 550,000 years ago.
'My results are consistent with the view that these super-archaics are descendants of that original out-of-Africa migration,' Professor Rogers said.
It is possible, then, that the mysterious 'super-archaic' hominin population may have been H. erectus, whose emergence 2 million years ago matches the researchers' estimated dating of the split between the super-archaics and other hominins.
Back in Africa, it is thought that the shared ancestors of Denisovans and Neanderthals, which are unknown in the fossil record, likely split from the ancestors of modern humans around 800,000 years ago.
The Neanderthal/Denisovans ancestors, which Professor Rogers has dubbed 'Neandersovans', would later have migrated out of Africa, eventually meeting up with the super-archaics — possibly H. erectus — with whom they mated.
It was only around 200,000 years ago that modern humans first migrated out of Africa and, in doing so, encountered both the Neanderthals and the Denisovans.
Modern humans likely never met any H. erectus, whom it is thought would have become extinct before the arrival of our direct ancestors.
'There’s good evidence that hybrids between either Neanderthals or Denisovans and modern humans seem to have been less healthy,' he said, explaining that evolution appears to have since weeded out many genes introduced by such interbreeding.
'Since the super-archaics had been separated even longer from Neandersovans, you might expect that that would have been a greater problem for them,' Professor Rogers added.
Professor Rogers and his colleagues' findings also suggest that fragments of DNA from the super-archaic populations might be preserved in Neanderthal genomes — and, by extension, potentially even in modern humans.
Any such remnants will be dispersed throughout the genome, however, making finding them difficult. 'I’m not going to say it’s impossible,' Professor Rogers said. But, he added, such would certainly be more of a challenge than finding the Neanderthal DNA many of us carry in small amounts.
Methodology/Principal Findings A 3-D geometric morphometric analysis of cranial landmarks and semilandmarks was conducted using a large comparative fossil and modern human sample. The measurements were collected in the form of three dimensional coordinates and processed using Generalized Procrustes Analysis. Principal components, canonical variates, Mahalanobis D2 and Procrustes distance analyses were performed. The results were further visualized by comparing specimen and mean configurations. Results point to a morphological similarity with late archaic African specimens dating to the Late Pleistocene. A long bone cortical fragment was made available for U-series analysis in order to re-date the specimen. The results (∼11.7–16.3 ka) support a terminal Pleistocene chronology for the Iwo Eleru burial as was also suggested by the original radiocarbon dating results and by stratigraphic evidence.
Conclusions/Significance Our findings are in accordance with suggestions of deep population substructure in Africa and a complex evolutionary process for the origin of modern humans. They further highlight the dearth of hominin finds from West Africa, and underscore our real lack of knowledge of human evolution in that region.
The Iwo Eleru burial was excavated from the Iwo Eleru rock shelter, south-western Nigeria, in 1965 by Thurstan Shaw and his team (Figure 1). The skeleton, preserving a calvaria, mandible and some postcranial remains, was found at a depth between 82 and 100 cm from the surface in an undisturbed Later Stone Age (hereafter LSA) context. Radiocarbon analysis of charcoal from the immediate vicinity of the burial resulted in an age estimate of 11,200±200 BP (∼13 ka calibrated). The skull was reconstructed and studied by Brothwell [1] (Figure 1)], who linked it to recent West African populations, though he recognized that its lower vault and frontal profile were unusual, and that the mandible was robust. The specimen is complete along the entire midline from nasion to beyond opisthocranion. Although it slightly asymmetric it shows no major distortions and the relatively well preserved mandible constrains its basal breadth. A preliminary multivariate analysis of cranial measurements by Peter Andrews (in [1]) suggested that the Iwo Eleru specimen was distinct from recent African groups.
Figure 1. Map of Nigeria, showing the geographic location of the Iwo Eleru rockshelter, and the Iwo Eleru calvaria.
A more extensive analysis of the cranial measurements of the original Iwo Eleru specimen was conducted by Chris Stringer, who included this cranium in univariate and multivariate (Canonical Variates, Generalised Distance) analyses for his doctoral thesis [2], [3]. Coefficients of separate determination in a cranial analysis using 17 of Howells' measures showed that the main discriminators from an Upper Paleolithic sample were low frontal subtense, low vertex radius, high cranial breadth, high bifrontal breadth, high cranial length and low parietal subtense, against Neanderthals they were primarily low supraorbital projection, low frontal fraction, high parietal chord, high frontal chord, low frontal subtense and low vertex radius, while against Zhoukoudian Homo erectus they were low supraorbital projection, high parietal chord, high bifrontal breadth, high vertex radius, high frontal chord and low frontal subtense. Overall it appeared that the cranium was “modern” in its low supraorbital projection, and long frontal and parietal chords, but “archaic” in its high cranial length, low vertex radius, and low frontal and parietal subtenses. Stringer's results highlighted apparent archaic aspects in the specimen in its long and rather low cranial shape, and although modern overall, it also resembled fossils such as Omo Kibish 2, Saccopastore 1 and Ngandong in several respects, falling closer to them than to Upper Palaeolithic and recent samples in some analyses (Figure 2).
Figure 2. Visualization of the results of Stringer's multivariate analyses [2], [3], showing the position of the Iwo Eleru calvaria.
In light of the redating of the LSA to a much deeper time depth than originally thought, and of the scarcity of LSA human skeletal remains from Africa in general and from West Africa in particular, we undertook a renewed study of the Iwo Eleru cranium with the aim of better determining its affinities and geological age [4], [5]. A primary replica of the cranial vault of the Iwo Eleru specimen, produced before its return to Nigeria, was digitized by one of the authors (KH). Comparisons of Stringer's measurements on the original and the replica show a maximum discrepancy of 1 mm, suggesting the replica accurately reflects the original shape of the cranium. The 3-D coordinates collected were included in an extensive comparative dataset of Middle, Late Pleistocene and Holocene humans, and a multivariate statistical analysis was undertaken with the goal of assessing its affinities and phylogenetic / population relationships in the context of geographic and temporal human cranial variation. Furthermore, in order to check the possibility that the associated radiocarbon age did not date the specimen, one of us (AF) provided a long bone cortical fragment approximate 1 cm square for a new age estimate. Unfortunately the lack of collagen prevented a direct radiocarbon determination at the Oxford Radiocarbon Accelerator, so Uranium-Series dating of the fragment was carried out instead.
