Shara E. Bailey

An early modern human from the Peştera cu Oase, Romania

The 2002 discovery of a robust modern human mandible in the Peştera cu Oase, southwestern Romania, provides evidence of early modern humans in the lower Danubian Corridor. Directly accelerator mass spectrometry radiocarbon (14C)-dated to 34,000–36,000 14C years B.P., the Oase 1 mandible is the oldest definite early modern human specimen in Europe and provides perspectives on the emergence and evolution of early modern humans in the northwestern Old World. The moderately long Oase 1 mandible exhibits a prominent tuber symphyseos and overall proportions that place it close to earlier Upper Paleolithic European specimens. Its symmetrical mandibular incisure, medially placed condyle, small superior medial pterygoid tubercle, mesial mental foramen, and narrow corpus place it closer to early modern humans among Late Pleistocene humans. However, its cross-sectional symphyseal orientation is intermediate between late archaic and early modern humans, the ramus is exceptionally wide, and the molars become progressively larger distally with exceptionally large third molars. The molar crowns lack derived Neandertal features but are otherwise morphologically undiagnostic. However, it has unilateral mandibular foramen lingular bridging, an apparently derived Neandertal feature. It therefore presents a mosaic of archaic, early modern human and possibly Neandertal morphological features, emphasizing both the complex population dynamics of modern human dispersal into Europe and the subsequent morphological evolution of European early modern humans.

Evolution of M1 crown size and cusp proportions in the genus Homo

Previous research into tooth crown dimensions and cusp proportions has proved to be a useful way to identify taxonomic differences in Pliocene and Pleistocene fossil hominins. The present study has identified changes in both M1 crown size and cusp proportions within the genus Homo, with M1 overall crown size reduction apparently occurring in two main stages. The first stage (a reduction of ca. 17%) is associated with the emergence of Homo ergaster and Homo erectus sensu stricto. The second stage (a reduction of ca. 10%) occurs in Homo sapiens, but the reduced modern human M1 tooth crown size was only attained in Upper Paleolithic times. The absolute sizes of the individual cusps are highly positively correlated with overall crown size and dental reduction produces a reduction in the absolute size of each of the cusps. Most of the individual cusps scale isometrically with crown size, but the paracone shows a negative allometric relationship, indicating that the reduction in paracone size is less than in the other M1 cusps. Thus, the phylogenetically oldest cusp in the upper molars also seems to be the most stable cusp (at least in the M1). The most striking change in M1 cusp proportions is a change in the relative size of the areas of the paracone and metacone. The combination of a small relative paracone and a large relative metacone generally characterizes specimens attributed to early Homo, and the presence of this character state in Australopithecus and Paranthropus suggests it may represent the primitive condition for the later part of the hominin clade. In contrast, nearly all later Homo taxa, with the exception of Homo antecessor, show the opposite condition (i.e. a relatively large paracone and a relatively small metacone). This change in the relationship between the relative sizes of the paracone and metacone is related to an isometric reduction of the absolute size of the metacone. This metacone reduction occurs in the context of relative stability in the paracone as crown size decreases. Among later Homo taxa, both Homo heidelbergensis and Homo neanderthalensis show a further reduction of the metacone and an enlargement of the hypocone. Fossil and contemporary H. sapiens samples show a trend toward increasing the relative size of the protocone and decreasing the relative size of the hypocone. In Europe, modern human M1 cusp proportions are essentially reached during the Upper Paleolithic. Although some variation was documented among the fossil taxa, we suggest that the relative size of the M1 paracone and metacone areas may be useful for differentiating the earliest members of our genus from subsequent Homo species.

Interobserver error involved in independent attempts to measure cusp base areas of Pan M1s.

Cusp base areas measured from digitized images increase the amount of detailed quantitative information one can collect from post‐canine crown morphology. Although this method is gaining wide usage for taxonomic analyses of extant and extinct hominoids, the techniques for digitizing images and taking measurements differ between researchers. The aim of this study was to investigate interobserver error in order to help assess the reliability of cusp base area measurement within extant and extinct hominoid taxa. Two of the authors measured individual cusp base areas and total cusp base area of 23 maxillary first molars (M1) of Pan. From these, relative cusp base areas were calculated. No statistically significant interobserver differences were found for either absolute or relative cusp base areas. On average the hypocone and paracone showed the least interobserver error (< 1%) whereas the protocone and metacone showed the most (2.6–4.5%). We suggest that the larger measurement error in the metacone/protocone is due primarily to either weakly defined fissure patterns and/or the presence of accessory occlusal features. Overall, levels of interobserver error are similar to those found for intraobserver error. The results of our study suggest that if certain prescribed standards are employed then cusp and crown base areas measured by different individuals can be pooled into a single database.

The affinity of the dental remains from Obi-Rakhmat Grotto, Uzbekistan

A human partial maxillary dentition and a fragmentary cranium were recovered from Obi-Rakhmat Grotto in northeastern Uzbekistan in 2003. Initial descriptions of this single juvenile (OR-1) from a Middle Paleolithic archaeological context have emphasized its mosaic morphological pattern; the dentition appears archaic, while certain morphological aspects of the cranial fragments may be more ambiguous. The present study provides a systematic and comparative analysis of the dental morphology and morphometrics of OR-1 to provide a more refined appraisal of its phenetic affinity vis á vis Neandertals and modern humans. Two analyses were performed. The first uses 28 non-metric dental traits scored from Neandertals, Upper Paleolithic, and Middle Paleolithic modern humans to assess the posterior probability of group membership for the Obi-Rakhmat individual. The second is a morphometric analysis of the first upper molar of OR-1. The results of both analyses suggest the dentition of OR-1 is essentially Neandertal.

New fossil remains of Homo naledi from the Lesedi Chamber, South Africa

The Rising Star cave system has produced abundant fossil hominin remains within the Dinaledi Chamber, representing a minimum of 15 individuals attributed to Homo naledi. Further exploration led to the discovery of hominin material, now comprising 131 hominin specimens, within a second chamber, the Lesedi Chamber. The Lesedi Chamber is far separated from the Dinaledi Chamber within the Rising Star cave system, and represents a second depositional context for hominin remains. In each of three collection areas within the Lesedi Chamber, diagnostic skeletal material allows a clear attribution to H. naledi. Both adult and immature material is present. The hominin remains represent at least three individuals based upon duplication of elements, but more individuals are likely present based upon the spatial context. The most significant specimen is the near-complete cranium of a large individual, designated LES1, with an endocranial volume of approximately 610 ml and associated postcranial remains. The Lesedi Chamber skeletal sample extends our knowledge of the morphology and variation of H. naledi, and evidence of H. naledi from both recovery localities shows a consistent pattern of differentiation from other hominin species. DOI: http://dx.doi.org/10.7554/eLife.24232.001

Dental evidence from the Aterian human populations of Morocco

The Aterian fossil hominins represent one of the most abundant series of human remains associated with Middle Stone Age/Middle Paleolithic assemblages in Africa. Their dates have been revised and they are now mostly assigned to a period between 90 and 35 ka. Although the Aterian human fossil record is exclusively Moroccan, Aterian assemblages are found throughout a vast geographical area extending to the Western Desert of Egypt. Their makers represent populations that were located close to the main gate to Eurasia and that immediately predated the last out-of-Africa exodus. In this chapter, we present an analysis of the Aterian dental remains. The sizes of the Aterian dentitions are particularly spectacular, especially for the post-canine dentition. This massiveness is reminiscent of the Middle Paleolithic modern humans from the Near East, but also of the early Homo sapiens in North and East Africa. Morphologically, this megadontia is expressed in the development of mass-additive traits. The Aterian dentition also displays relatively thick enamel. These features help to set some of the traits observed in Neandertals in perspective and highlight their primitive or derived nature. The Aterian morphological pattern is also important to consider when interpreting the dental morphology of the first modern humans in Eurasia.

Allometry, merism, and tooth shape of the lower second deciduous molar and first permanent molar

OBJECTIVES This study investigates the effect of allometry on the shape of lower dm2 (dm2) and lower M1 (M1) crown outlines and examines whether the trajectory and magnitude of allometric scaling are shared between Neandertals and Homo sapiens. METHODS Our sample included 164 specimens: 57 recent H. sapiens, 44 Upper Paleolithic H. sapiens, 17 early H. sapiens, and 46 Neandertals. Of these, 59 represent dm2/M1 pairs from the same individuals. Occlusal photographs were used to obtain crown shapes of dm2s and M1s. Principal components analysis (PCA) of the matrix of shape coordinates was used to explore the pattern of morphological variation across the dm2 and M1 samples. Allometry was investigated by means of the Pearson product-moment correlation coefficient. Two-block partial least squares (2B-PLS) analysis was used to explore patterns of covariation between dm2 and M1 crown outlines of matched individual pairs. RESULTS The PCA confirmed significant differences between Neandertal and H. sapiens dm2 and M1 shapes. Allometry accounted for a small but statistically significant proportion of the total morphological variance. The magnitude of the allometric contribution to crown shape was stronger among Neandertals than among H. sapiens. However, we could not reject the null hypothesis that the two species share the same allometric trajectory. The 2B-PLS analysis of the pooled sample of paired individuals revealed a significant correlation in crown shape between dm2 and M1. While Procrustes distances differed significantly between dm2 and M1 in Neandertals, it did not among H. sapiens groups. CONCLUSIONS Our results confirm several of the results obtained by a similar study of upper dm2/M1 (dm(2)/M(1)), but there are differences as well. Neandertal dm2/M1 shapes are less derived than those of the dm(2)/M(1). Such differences may support previous studies, which have suggested that different developmental and/or epigenetic factors affect the upper and lower dentitions.

Brief communication: A morphometric analysis of the neandertal upper second molar leuca I

The scarcity of Neandertal remains from Southern Europe hampers our understanding of Neandertal variability, and can bias interpretations about Neandertal geographic variation. To address this issue, it is often important to reassess human remains that, while discovered decades ago, remain relatively unknown to the scientific community. In this contribution, we provide a complete state-of-the-art comparative morphometric analysis of Leuca I, an unworn left second upper molar (LM(2) ) discovered in 1958 in Bambinos Cave (near Santa Maria di Leuca, Apulia, Italy) and attributed to Homo neanderthalensis. Our study includes comparisons of standard metric and nonmetric data, a 2D image analysis of the occlusal surface and measurements of both 2D and 3D enamel thickness and dental tissue proportions. Although Leuca I follows the Neandertal M(2) s trend in some morphometric aspects (i.e., small relative occlusal polygon area), in other cases it falls to the higher end (for 3D average enamel thickness) or even outside (for 3D-relative enamel thickness) the Neandertal M(2) variability, thus increasing the known Neandertal range of variation.

Dental Development and Age at Death of a Middle Paleolithic Juvenile Hominin from Obi-Rakhmat Grotto, Uzbekistan

Studies of dental development have reported conflicting results regarding whether Neanderthal growth and development was similar to that of modern humans. The discovery of a partial permanent maxillary juvenile dentition (OR-1) from the Obi-Rakhmat Grotto, Uzbekistan, provides the opportunity to assess dental development and age at death in a Paleolithic hominin with strong Neanderthal similarities using incremental dental features. Long-period lines on tooth crowns (perikymata) and roots (periradicular bands) were quantified, and crown formation, root development, and age at death were estimated. An anomalous upper molar was determined to be a left M2 with a rare developmental condition (gemination). Perikymata numbers for OR-1 were similar to modern southern African population means, but were less than modern northern European and Neanderthal means. Root extension rates were estimated to be similar to (or slightly higher than) modern human values, although few modern comparative data are available. Assuming the long-period line periodicity of this individual fell within a Neanderthal distribution (6–9 days), the maximum age at death of OR-1 is estimated at 8.1 years, but is more likely to have been 6.7–7.4 years (7 or 8 day periodicity). Modern European human developmental standards would suggest an age at death of approximately 8–9 years. These results are consistent with other studies suggesting that Neanderthal dental development overlaps with the low end of modern human populations, and demonstrates a greater range of variation in Middle Paleolithic hominins than previously reported. It is clear that perikymata number alone does not distinguish these taxa; data on long-period line periodicity and molar eruption would yield additional insight into Neanderthal life history.

Did Neanderthals make the Châtelperronian assemblage from La Grotte du Renne (Arcy-sur-Cure, France)?

Much debate has focused on the significance of the “modern” cultural elements found in European Late Middle Paleolithic (Châtelperronian, Uluzzian, and Szeletian) contexts. In light of evidence suggesting cultural interaction between the makers of these industries and the makers of the Aurignacian (presumably anatomically modern humans) it is imperative that the taxonomic affiliation of the hominins associated with these “transitional” industries be accurately identified. The fossil remains from the Châtelperronian levels (VIII-X) at the Grotte du Renne (Arcy-sur-Cure, France) comprise a series of isolated teeth, as well as a child’s temporal bone. While the temporal bone has been analyzed (and identified as having Neanderthal affinity), most of the 29 teeth from these levels have not been described. The Châtelperronian dental remains from the Grotte du Renne comprise both permanent and deciduous teeth. Fortunately, most are well preserved and relatively unworn. Simple dental dimensions are not particularly helpful in attempts to differentiate between Neanderthals and anatomically modern humans. The dimensions of the postcanine teeth in these two groups overlap completely. However, Neanderthals are known to have larger anterior teeth (on average), especially relative to their postcanine tooth size. Not surprisingly, we find that the crown dimensions for the postcanine teeth from the Grotte du Renne fall within the ranges of both hominin groups. The crown dimensions of the anterior teeth, however, strongly suggest that they belong to Neanderthal individuals. The buccolingual measurements of all but one tooth fall outside the range of Upper Paleolithic modern humans and 191