Artificial neural networks reconstruct missing perikymata in worn teeth.

Dental evolutionary studies in hominins are key to understanding how our ancestors and close fossil relatives grew from the early stages of embryogenesis into adults. In a sense, teeth are like an airplane's 'black box' as they record important variables for assessing developmental timing, enabling comparisons within and between populations, species, and genera. The ability to discern this type of nuanced information is embedded in the nature of how tooth enamel and dentin form: incrementally and over years. This incremental growth leaves chronological indicators in the histological structure of enamel, visible on the crown surface as perikymata. These structures are used in the process of reconstructing the rate and timing of tooth formation. Unfortunately, the developmentally earliest growth lines in lateral enamel are quickly lost to wear once the tooth crown erupts. We developed a method to reconstruct these earliest, missing perilymata from worn teeth through knowledge of the later-developed, visible perikymata for all tooth types (incisors, canines, premolars, and molars) using a modern human dataset. Building on our previous research using polynomial regressions, here we describe an artificial neural networks (ANN) method. This new ANN method mostly predicts within 2 counts the number of perikymata present in each of the first three deciles of the crown height for all tooth types. Our ANN method for estimating perikymata lost through wear has two immediate benefits: more accurate values can be produced and worn teeth can be included in dental research. This tool is available on the open-source platform R within the package teethR released under GPL v3.0 license, enabling other researchers the opportunity to expand their datasets for studies of periodicity in histological growth, dental development, and evolution.

Sexual dimorphism in the enamel-dentine junction (EDJ) of permanent canines of European modern humans.

OBJECTIVES: Dental anthropological investigations into sexual dimorphism have conventionally concentrated on evaluating the dimensions and configuration of the enamel cap of canines. However, the morphology of the crown dentine surface can be closely linked to that of the enamel surface. This link can facilitate examination of crown morphology even when the enamel surface is slightly worn. Here, we determine if the morphology of the enamel-dentine junction (EDJ) differs within (maxillary vs. mandibular) and between a sample of male (n = 26) and female (n = 21) contemporary human permanent canines from Europe. METHODS: The morphological data of the EDJ were gathered employing a template comprising 96 landmarks and sliding semilandmarks. Subsequently, the data underwent analysis through form space principal component analysis following Procrustes registration, utilizing standard 3D geometric morphometric techniques. RESULTS: Significant differences in the morphology of the EDJ were observed between the sexes, particularly concerning the overall shape of the crown, the symmetry of the mesial and distal edges, and the development of the distal accessory ridge. CONCLUSIONS: Sex differences in the morphology of the EDJ could relate in part to retention of the canine-premolar honing complex in males. Our results indicate that analyses of the permanent canine EDJ may potentially provide a novel method for estimating the sex of adult and nonadult skeletons.

Morphological and morphometric analyses of a late Middle Pleistocene hominin mandible from Hualongdong, China.

Excavations in Hualongdong (HLD), East China, have yielded abundant hominin fossils dated to 300 ka. There is a nearly complete mandible that fits well with a partial cranium, and together they compose the skull labeled as HLD 6. Thus far, detailed morphological description and comparisons of the mandible have not been conducted. Here we present a comprehensive morphological, metric, and geometric morphometric assessment of this mandible and compare it with both adult and immature specimens of Pleistocene hominins and recent modern humans. Results indicate that the HLD 6 mandible exhibits a mosaic morphological pattern characterized by a robust corpus and relatively gracile symphysis and ramus. The moderately developed mental trigone and a clear anterior mandibular incurvation of the HLD 6 mandible are reminiscent of Late Pleistocene hominin and recent modern human morphology. However, the weak expression of all these features indicates that this mandible does not possess a true chin. Moreover, a suite of archaic features that resemble those of Middle Pleistocene hominins includes pronounced alveolar planum, superior transverse torus, thick corpus, a pronounced endocondyloid crest, and a well-developed medial pterygoid tubercle. The geometric morphometric analysis further confirms the mosaic pattern of the HLD 6 mandible. The combination of both archaic and modern human features identified in the HLD 6 mandible is unexpected, given its late Middle Pleistocene age and differs from approximately contemporaneous Homo members such as Xujiayao, Penghu, and Xiahe. This mosaic pattern has never been recorded in late Middle Pleistocene hominin fossil assemblages in East Asia. The HLD 6 mandible provides further support for the high morphological diversity during late Middle Pleistocene hominin evolution. With these findings, it is possible that modern human morphologies are present as early as 300 ka and earlier than the emergence of modern humans in East Asia.

Frontal sinuses and human evolution.

The frontal sinuses are cavities inside the frontal bone located at the junction between the face and the cranial vault and close to the brain. Despite a long history of study, understanding of their origin and variation through evolution is limited. This work compares most hominin species' holotypes and other key individuals with extant hominids. It provides a unique and valuable perspective of the variation in sinuses position, shape, and dimensions based on a simple and reproducible methodology. We also observed a covariation between the size and shape of the sinuses and the underlying frontal lobes in hominin species from at least the appearance of Homo erectus. Our results additionally undermine hypotheses stating that hominin frontal sinuses were directly affected by biomechanical constraints resulting from either chewing or adaptation to climate. Last, we demonstrate their substantial potential for discussions of the evolutionary relationships between hominin species.

Comparing the Boxgrove and Atapuerca (Sima de los Huesos) human fossils: Do they represent distinct paleodemes?

The early Middle Pleistocene human material from Boxgrove (West Sussex, UK) consists of a partial left tibia and two lower incisors from a separate adult individual. These remains derive from deposits assigned to the MIS 13 interglacial at about 480 ka and have been referred to as Homo cf. heidelbergensis. The much larger skeletal sample from the Sima de los Huesos (Atapuerca, Spain) is dated to the succeeding MIS 12, at about 430 ka. This fossil material has previously been assigned to Homo heidelbergensis but is now placed within the Neanderthal clade. Because of the scarcity of human remains from the Middle Pleistocene and their morphological variability, this study assessed whether the Boxgrove specimens fit within the morphological variability of the homogeneous Sima de los Huesos population. Based on morphometric analyses performed against 22 lower incisors from Sima de los Huesos and published material, the data from the Boxgrove incisors place them comfortably within the range of Sima de los Huesos. Both assemblages present robust incisors distinct from the overall small recent Homo sapiens incisors, and Boxgrove also aligns closely with Homo neanderthalensis and some other European Middle Pleistocene hominins. Following morphological and cross-sectional analyses of the Boxgrove tibia compared to seven adult Sima de los Huesos specimens and a set of comparative tibiae, Boxgrove is shown to be similar to Sima de los Huesos and Neanderthals in having thick cortices and bone walls, but in contrast resembles modern humans in having a straight anterior tibial crest and a suggestion of a lateral concavity. Based on the patterns observed, there is no justification for assigning the Boxgrove and Sima de los Huesos incisors to distinct paleodemes, but the tibial data show greater contrasts and suggest that all three of these samples are unlikely to represent the same paleodeme.

Early Pleistocene hominin teeth from Gongwangling of Lantian, Central China.

The fossil hominin individual from Gongwangling of Lantian, Central China, represents one of the earliest members attributed to Homo erectus in East Asia. Recent paleomagnetic analyses have yielded an age of 1.63 Ma for the Gongwangling hominin. The fossils from this site are critical to characterize the morphological features of early hominins in East Asia and to understand their relationships with other earlier and later members of the genus Homo. However, most morphological details of the Gongwangling cranium were obliterated due to postmortem erosion and deformation. Here we used high-resolution microcomputed tomography and three-dimensional virtual imaging techniques to extract the teeth and reconstruct the worn/damaged areas, describe the external morphology, measure crown diameters, record nonmetric traits of the crown and root, and investigate the shape of the enamel-dentine junction using geometric morphometrics. We compared the data obtained from the six teeth of the Gongwangling hominin with African early Homo, African and Georgian Homo erectus s.l., Asian Homo erectus, Homo antecessor, pre-Neanderthals, Neanderthals, and modern humans. Our results show that the Gongwangling specimens display affinities with other specimens attributed to H. erectus s.l. The highly divergent and noncoalesced three-root system in the Gongwangling specimens is comparable to that in the Early Pleistocene members of H. erectus s.l., and differs from Middle Pleistocene representatives of the species. The enamel-dentine junction shape of the Gongwangling molars prefigures the Asian H. erectus pattern later found in East Asian Middle Pleistocene H. erectus. The morphological comparisons between East Asian Early Pleistocene (e.g., Gongwangling, Meipu, and Quyuan River Mouth) and Middle Pleistocene H. erectus (e.g., Zhoukoudian, Hexian, and Yiyuan) suggest a potential temporal trend within this species in East Asia.

The protoconid: a key cusp in lower molars. Evidence from a recent modern human population.

BACKGROUND: The molar (M) size sequence in the genus Homo is decreasing and the general pattern in Homo sapiens is M1> M2 > M3. AIM: To gain a better understanding of the reduction patterns of M components (cusps), we aim to assess the area of the protoconid (Prd), the phylogenetically oldest cusp of the lower Ms. SUBJECT AND METHODS: We measured the Prd and the total crown area in the scaled photographs of a recent modern human sample of lower Ms (76 males and 39 females). The values were statistically analysed. RESULTS: The absolute size of the Prd increases significantly between M1 and M2/M3, whereas the relative size of this cusp increases significantly from M1 to M3. In the latter, reduction or disappearance of the cusps of the talonid is common. CONCLUSIONS: The results can be explained in the framework of the patterning cascade model. As the first cusp to appear developmentally, the Prd forms in response to signals from the primary enamel knot, likely contributing to its stability. Inhibitory signals emitted during the Prd formation may lead to the reduction or disappearance of the talonid cusps, if these do not have enough time to form before the end of the M morphogenetic process.

Similarities and differences in the dental tissue proportions of the deciduous and permanent canines of Early and Middle Pleistocene human populations.

The two- and three-dimensional assessment of dental tissues has become routine in human taxonomic studies throughout the years. Nonetheless, most of our knowledge of the variability of the enamel and dentine dimensions of the human evolutionary lineage comes from the study of permanent dentition, and particularly from molars. This leads to a biased view of the variability of these features. Due to their early formation and rapid development, the deciduous teeth allow more simplified inferences regarding the processes involved in the dental tissue development of each group. Therefore, their study could be very valuable in dental palaeohistology. In this research, we have explored the dental tissue proportions of the deciduous canines belonging to some human samples of the Early and Middle Pleistocene. The purpose of this was to discuss the meaning of the similarities and differences observed in their histological pattern, as well as to evaluate the degree of covariance with that observed in the permanent dentition of these populations. Our results show that, although there are some similarities in the dental tissue proportions between the deciduous and permanent canines of the study samples, the two dental classes do not provide a similar or comparable pictures of the dental tissue pattern present in the dentition of fossil hominins. Future works on the dental tissue patterns of the anterior and posterior dentition, including deciduous teeth, of fossil samples, may help to shed light on this hypothesis.

Dental remains of the Middle Pleistocene hominins from the Sima de los Huesos site (Sierra de Atapuerca, Spain): Mandibular dentition.

The Middle Pleistocene site of the Sima de los Huesos (Sierra de Atapuerca, northern Spain) has yielded a considerable number of human fossils during the period 1984-2020. Among them, up to 314 mandibular teeth have been identified. In this second paper dedicated to the dentition we present the description of the eight dental classes of the mandible following the Arizona State University Dental Anthropology System (ASUDAS) classification. In addition, we show the mean mesiodistal and buccolingual diameters obtained in these teeth compared to those of Neanderthals and a modern human sample. The morphology of both the anterior and posterior teeth suggests a close relationship of the Sima de los Huesos hominins with the populations of the second half of the Middle Pleistocene of Europe and the Near East, as well as with the so-called classic Neanderthals of Europe. The combination of dental traits in these populations is characteristic and diagnostic and suggests grouping the Sima de los Huesos hominins with the other paleodemes in a Neanderthal clade. The dental evidence of the Sima de los Huesos hominins is key to propose a complex model for the settlement of Europe during the Middle Pleistocene. In this period, different migrations of human groups probably coming from Southwest Asia, replacements, prolonged isolations, as well as hybridization and introgression processes would have contributed to the diversity of hominins in Europe.

Response to Comment on "A Middle Pleistocene Homo from Nesher Ramla, Israel".

Marom and Rak claim, on the basis of a few mandibular features, that the Nesher Ramla (NR) Homo is a Neanderthal. Their comments lack substance and contribute little to the debate surrounding the evolution of Middle Pleistocene Homo. Limitations and preconceptions in their study prevented them from achieving resolution beyond a dichotomous interpretation of the NR as either a Neanderthal or a modern human.

Dental remains of the Middle Pleistocene hominins from the Sima de los Huesos site (Sierra de Atapuerca, Spain): Maxillary dentition.

The Middle Pleistocene site of the Sima de los Huesos (Sierra de Atapuerca, northern Spain) has yielded a considerable number of human fossils during the period 1984-2020. Among them, up to 253 maxillary teeth have been recovered. In this article, we present the description of the eight dental classes of the maxilla following the Arizona State University Dental Anthropology System classification. In addition, we present the mean mesiodistal and buccolingual diameters of these teeth compared to those of Neanderthals and a modern human sample. The morphology of both the anterior and posterior teeth suggests a close relationship of the Sima de los Huesos hominins with the populations of the second half of the Middle Pleistocene of Europe and the Near East, as well as with the so-called classic Neanderthals of Europe. Features with a recognizable taxonomic signal allow grouping the Sima de los Huesos hominins with different paleodemes into a Neanderthal clade. The dental evidence of the Sima de los Huesos hominins is key to suggest a complex model for the settlement of Europe during the Middle Pleistocene. During this period, different migrations of human groups probably coming from Southwest Asia, replacements, prolonged isolations, as well as hybridization and introgression processes would have contributed to the diversity of hominins in Europe.

Comparative dental study between Homo antecessor and Chinese Homo erectus: Nonmetric features and geometric morphometrics.

The Chinese Middle Pleistocene fossils from Hexian, Xichuan, Yiyuan, and Zhoukoudian have been generally classified as Homo erectus s.s. These hominins share some primitive features with other Homo specimens, but they also display unique cranial and dental traits. Thus, the Chinese Middle Pleistocene hominins share with other European and Asian hominin populations the so-called 'Eurasian dental pattern'. The late Early Pleistocene hominins from Gran Dolina-TD6.2 (Spain), representing the species Homo antecessor, also exhibit the Eurasian dental pattern, which may suggest common roots. To assess phylogenetic affinities of these two taxa, we evaluated and compared nonmetric and metric dental features and interpreted morphological differences within a comparative hominin framework. We determined that the robust roots of the molars, the shelf-like protostylid, the dendrite-like pattern of the enamel-dentine junction surface of the upper fourth premolars and molars, the strongly folded dentine of the labial surface of the upper incisors, and the rare occurrence of a mid-trigonid crest in the lower molars, are all characteristic of Chinese H. erectus. With regard to H. antecessor, we observed the consistent expression of a continuous mid-trigonid crest, the absence of a cingulum in the upper canines, a complex root pattern of the lower premolars, and a rhomboidal occlusal contour and occlusal polygon and protrusion in the external outline of a large a bulging hypocone in the first and second upper molars. Using two-dimensional geometric morphometrics, we further demonstrated that H. antecessor falls outside the range of variation of Chinese H. erectus for occlusal crown outline shape, the orientation of occlusal grooves, and relative locations of anterior and posterior foveae in the P4s, P3s, M1s, M2s, and M2s. Given their geographic and temporal separation, the differences between these two species suggest their divergence occurred at some point in the Early Pleistocene, and thereafter they followed different evolutionary paths.

The Ratón Pérez collection: Modern deciduous human teeth at the Centro Nacional de Investigación sobre la Evolución Humana (Burgos, Spain).

OBJECTIVES: The aim of this report is to present the large deciduous tooth collection of identified children that is housed at the National Research Center on Human Evolution (CENIEH) in Burgos, Spain. METHODS: Yearly, members of the Dental Anthropology Group of the CENIEH are in charge of collecting the teeth and registering all the relevant information from the donors at the time of collection. In compliance with Spanish Law 14/2007 of July 3, 2007, on Biomedical Research (BOE-A-2007-12945), all individuals are guaranteed anonymity and confidentiality. When the donor hands in the tooth, they fill out a Donor Information Form and sign the Informed Consent Form. At the same time, another person completes the data label for the transparent polyethylene zip lock bag where the tooth is temporarily stored. All teeth are then transferred to the CENIEH Restoration lab, where the specialists apply the same protocol as for the fossil remains. RESULTS: Although the sample is still growing, from the first collection campaign in 2014 to date it comprises 2977 teeth of children whose ages of tooth loss are between 2 and 15 years. Each tooth is associated with basic information of the individuals and their parents and grandparents (sex, date, and place of birth, ancestry, country of residence), as well as important data about early life history (pregnancy duration, breastfeeding, bottle-feeding) and other relevant information provided by the donors (such as if they are twins, dental loss, or dental extraction). CONCLUSIONS: Due to the scarcity of deciduous dental samples available, the Ratón Pérez collection represents a highly valuable sample for a wide range of disciplines such as forensic, dental, and anthropological fields among others.

Testing the inhibitory cascade model in a recent human sample.

The Inhibitory Cascade Model was proposed by Kavanagh and colleagues (Nature, 449, 427-433 [2007]) after their experimental studies on the dental development of murine rodent species. These authors described an activator-inhibitor mechanism that has been employed to predict evolutionary size patterns of mammalian teeth, including hominins. In the present study, we measured the crown area of the three lower permanent molars (M1, M2, and M3) of a large recent modern human sample of male and female individuals from a collection preserved at the Institute of Anthropology of the University of Coimbra (Portugal). The main aim of the present study is to test if the size molar patterns observed in this human sample fits the Inhibitory Cascade Model. For this purpose, we first measured the crown area in those individuals preserving the complete molar series. Measurements were taken in photographs, using a planimeter and following well-tested techniques used in previous works. We then plot the M3 /M1 and M2 /M1  size ratios. Our results show that the premise of the Inhibitory Cascade Model, according to which the average of the crown area of M2 is approximately one-third of the sum of the crown area of the three molars, is fulfilled. However, our results also show that the individual values of a significant number of males and females are out of the 95% confidence interval predicted by the Inhibitory Cascade Model in rodents. As a result, the present analyses suggest that neither the sample of males, nor that of females, nor the pooled sample fits the Inhibitory Cascade Model. It is important to notice that, although this model has been successfully tested in a large number of current human populations, to the best of our knowledge this is the first study in which individual data have been obtained in a recent human population rather than using the average of the sample. Our results evince that, at the individual level, some factors not yet known could interfere with this model masking the modulation of the size on the molar series in modern humans. We suggest that the considerable delay in the onset of M3 formation in modern humans could be related to a weakening of the possible activation/inhibition process for this tooth. Finally, and in support of our conclusions, we have checked that the absolute and relative size of M1 and M2 is not related to the M3 agenesis in our sample. In line with other studies in primates, our results do not support the Inhibitory Cascade Model in a recent human sample. Further research is needed to better understand the genetic basis of this mechanism and its relationship to the phenotype. In this way, we may be able to find out which evolutionary changes may be responsible for the deviations observed in many species, including Homo sapiens.

Earliest known human burial in Africa.

The origin and evolution of hominin mortuary practices are topics of intense interest and debate1-3. Human burials dated to the Middle Stone Age (MSA) are exceedingly rare in Africa and unknown in East Africa1-6. Here we describe the partial skeleton of a roughly 2.5- to 3.0-year-old child dating to 78.3 ± 4.1 thousand years ago, which was recovered in the MSA layers of Panga ya Saidi (PYS), a cave site in the tropical upland coast of Kenya7,8. Recent excavations have revealed a pit feature containing a child in a flexed position. Geochemical, granulometric and micromorphological analyses of the burial pit content and encasing archaeological layers indicate that the pit was deliberately excavated. Taphonomical evidence, such as the strict articulation or good anatomical association of the skeletal elements and histological evidence of putrefaction, support the in-place decomposition of the fresh body. The presence of little or no displacement of the unstable joints during decomposition points to an interment in a filled space (grave earth), making the PYS finding the oldest known human burial in Africa. The morphological assessment of the partial skeleton is consistent with its assignment to Homo sapiens, although the preservation of some primitive features in the dentition supports increasing evidence for non-gradual assembly of modern traits during the emergence of our species. The PYS burial sheds light on how MSA populations interacted with the dead.

Indicators of sexual dimorphism in Homo antecessor permanent canines.

One of the main concerns of paleoanthropologists is to make a correct interpretation of the variability observed in the fossil record. However, the current knowledge about sexual dimorphism in the human lineage comes mainly from the study of modern human, Neanderthal and pre-Neanderthal populations, whereas information available about the intrapopulation variability of the groups that preceded these taxa is still ambiguous. In this preliminary study, Homo antecessor dental sample was assessed with the aim of trying to evaluate the degree of variability of their permanent canines` dental tissue proportions. Microtomographic techniques were here employed in order to measure and compare the crown volumes and surface areas of their enamel caps and dentine-pulp complexes. Then, the Pearson`s Coefficient of Variation and the Euclidean Distance were assessed to evaluate of intrapopulation variability of Gran Dolina TD6.2 dental sample. The values obtained were also compared with those of the dental samples from Sima de los Huesos site (Spain), the Neanderthal site of Krapina (Croatia), as well as from a broad forensic collection of known sex. Our results showed a marked intrapopulation variability in the dental tissues measurements of the canines of the individuals H1 and H3 from this site. This variability may be interpreted as an indicator of sexual dimorphism. If this is the case, H1 may be considered as a male individual, whereas H3 would be a female. Future discoveries of new fossils in the level TD6.2 of Gran Dolina site might help to confirm or refute this hypothesis.

Neanderthals and Homo sapiens had similar auditory and speech capacities.

The study of audition in fossil hominins is of great interest given its relationship with intraspecific vocal communication. While the auditory capacities have been studied in early hominins and in the Middle Pleistocene Sima de los Huesos hominins, less is known about the hearing abilities of the Neanderthals. Here, we provide a detailed approach to their auditory capacities. Relying on computerized tomography scans and a comprehensive model from the field of auditory bioengineering, we have established sound power transmission through the outer and middle ear and calculated the occupied bandwidth in Neanderthals. The occupied bandwidth is directly related to the efficiency of the vocal communication system of a species. Our results show that the occupied bandwidth of Neanderthals was greater than the Sima de los Huesos hominins and similar to extant humans, implying that Neanderthals evolved the auditory capacities to support a vocal communication system as efficient as modern human speech.

Evolutionary development of the Homo antecessor scapulae (Gran Dolina site, Atapuerca) suggests a modern-like development for Lower Pleistocene Homo.

Two well-preserved, subadult 800 ky scapulae from Gran Dolina belonging to Homo antecessor, provide a unique opportunity to investigate the ontogeny of shoulder morphology in Lower Pleistocene humans. We compared the H. antecessor scapulae with a sample of 98 P. troglodytes and 108 H. sapiens representatives covering seven growth stages, as well as with the DIK-1-1 (Dikika; Australopithecus afarensis), KNM-WT 15000 (Nariokotome; H. ergaster), and MH2 (Malapa; A. sediba) specimens. We quantified 15 landmarks on each scapula and performed geometric morphometric analyses. H. sapiens scapulae are mediolaterally broader with laterally oriented glenoid fossae relative to Pan and Dikika shoulder blades. Accordingly, H. antecessor scapulae shared more morphological affinities with modern humans, KNM-WT 15000, and even MH2. Both H. antecessor and modern Homo showed significantly more positive scapular growth trajectories than Pan (slopes: P. troglodytes = 0.0012; H. sapiens = 0.0018; H. antecessor = 0.0020). Similarities in ontogenetic trajectories between the H. antecessor and modern human data suggest that Lower Pleistocene hominin scapular development was already modern human-like. At the same time, several morphological features distinguish H. antecessor scapulae from modern humans along the entire trajectory. Future studies should include additional Australopithecus specimens for further comparative assessment of scapular growth trends.