Search

Characterizing dental development in fossil hominins is important for distinguishing between them and for establishing where and when the slow overall growth and development of modern humans appeared. Dental development of australopiths and early Homo was faster than modern humans. The Atapuerca fossils (Spain) fill a barely known gap in human evolution, spanning ~1.2 to ~0.4 million years (Ma), during which H. sapiens and Neandertal dental growth characteristics may have developed. We report here perikymata counts, perikymata distributions and periodicities of all teeth belonging to the TE9 level of Sima del Elefante, level TD6.2 of Gran Dolina (H. antecessor) and Sima de los Huesos. We found some components of dental growth in the Atapuerca fossils resembled more recent H. sapiens. Mosaic evolution of perikymata counts and distribution generate three distinct clusters: H. antecessor, Sima de los Huesos and H. sapiens. [ABSTRACT FROM AUTHOR]

Objectives In the last years different methodologies have been developed to reconstruct worn teeth. In this article, we propose a new 2-D methodology to reconstruct the worn enamel of lower molars. Our main goals are to reconstruct molars with a high level of accuracy when measuring relevant histological variables and to validate the methodology calculating the errors associated with the measurements. Methods This methodology is based on polynomial regression equations, and has been validated using two different dental variables: cuspal enamel thickness and crown height of the protoconid. In order to perform the validation process, simulated worn modern human molars were employed. The associated errors of the measurements were also estimated applying methodologies previously proposed by other authors. Results The mean percentage error estimated in reconstructed molars for these two variables in comparison with their own real values is −2.17% for the cuspal enamel thickness of the protoconid and −3.18% for the crown height of the protoconid. This error significantly improves the results of other methodologies, both in the interobserver error and in the accuracy of the measurements. Conclusions The new methodology based on polynomial regressions can be confidently applied to the reconstruction of cuspal enamel of lower molars, as it improves the accuracy of the measurements and reduces the interobserver error. The present study shows that it is important to validate all methodologies in order to know the associated errors. This new methodology can be easily exportable to other modern human populations, the human fossil record and forensic sciences. [ABSTRACT FROM AUTHOR]

An important question in palaeoanthropology is whether, among the australopiths and the first fossil hominins attributed to early Homo, there was a shift towards a more prolonged period of growth that can be distinguished from that of the living great apes and whether between the end of weaning and the beginning of puberty there was a slow period of growth as there is in modern humans. Evidence for the pace of growth in early fossil hominins comes from preserved tooth microstructure. A record of incremental growth in enamel and dentine persists, which allows us to reconstruct tooth growth and compare key measures of dental maturation with modern humans and living great apes. Despite their diverse diets and way of life, it is currently difficult to identify any clear differences in the timing of dental development among living great apes, australopiths and the earliest hominins attributed to the genus Homo. There is, however, limited evidence that some early hominins may have attained a greater proportion of their body mass and stature relatively earlier in the growth period than is typical of modern humans today. This article is part of the themed issue 'Major transitions in human evolution'. [ABSTRACT FROM AUTHOR]

Besides Homo erectus (sensu lato), the eastern African fossil record of early Homo has been interpreted as representing either a single variable species, Homo habilis, or two species. In the latter case, however, there is no consensus over the respective groupings, and which of the two includes OH 7, the 1.8-million-year-old H. habilis holotype. This partial skull and hand from Olduvai Gorge remains pivotal to evaluating the early evolution of the Homo lineage, and by priority names one or other of the two taxa. However, the distorted preservation of the diagnostically important OH 7 mandible has hindered attempts to compare this specimen with other fossils. Here we present a virtual reconstruction of the OH 7 mandible, and compare it to other early Homo fossils. The reconstructed mandible is remarkably primitive, with a long and narrow dental arcade more similar to Australopithecus afarensis than to the derived parabolic arcades of Homo sapiens or H. erectus. We find that this shape variability is not consistent with a single species of early Homo. Importantly, the jaw morphology of OH 7 is incompatible with fossils assigned to Homo rudolfensis and with the A.L. 666-1 Homo maxilla. The latter is morphologically more derived than OH 7 but 500,000 years older, suggesting that the H. habilis lineage originated before 2.3 million years ago, thus marking deep-rooted species diversity in the genus Homo. We also reconstructed the parietal bones of OH 7 and estimated its endocranial volume. At between 729 and 824 ml it is larger than any previously published value, and emphasizes the near-complete overlap in brain size among species of early Homo. Our results clarify the H. habilis hypodigm, but raise questions about its phylogenetic relationships. Differences between species of early Homo appear to be characterized more by gnathic diversity than by differences in brain size, which was highly variable within all taxa. [ABSTRACT FROM AUTHOR]

The objectives of this study were to quantify the variation in coincident stages of incisor, canine and molar eruption and tooth formation in modern humans and great apes and then to ask if any early fossil hominins showed a dental development pattern beyond the human range and/or clearly typical of great apes. Four stages of eruption and 18 stages of tooth development were defined and then scored for each developing tooth on radiographs of 159 once-free-living subadult great apes and on orthopantomographs of 4091 dental patients aged 1–23 years. From original observations, and from published images of eleven early fossil hominins, we then scored formation stages of permanent incisors when M1 was at root formation stage R¼-R½ and R¾-RC. Incisor and canine eruption/development was delayed in great apes relative to molar development when compared with humans but there was overlap in almost all anterior tooth stages observed. Molar crown initiation was generally advanced in great apes and delayed in humans but again, we observed overlap in all stages in both samples. Only two fossil hominin specimens (L.H.–3 from Laetoli, Tanzania and KNM-KP 34725 from Kanapoi, Kenya) showed delayed incisor development relative to M1 beyond any individuals observed in the human sample. For certain tooth types, the distribution of formation stages in our samples showed evidence of generally advanced or delayed development between taxa. However, it would rarely if ever be possible to allocate an individual to one taxon or another on this basis. • Great ape canine and incisor eruption/development is delayed compared with humans. • Great ape molar development is relatively advanced compared with humans. • There is near-complete overlap of tooth formation stages in great apes and humans. • Individuals can't be assigned to a pattern of great ape or human dental development. • Fossil hominin incisor development is not advanced or delayed beyond the human range. [ABSTRACT FROM AUTHOR]

The aim of this study was to describe similarities and differences in the way modern and fossil hominin teeth grow in height. Measurements from longitudinal ground sections of 7 modern human canines and 19 first permanent molars were used to calculate extension rates in the crowns and roots and to plot distance curves for growth in tooth height. These were compared with identical data for 3 fossil hominin teeth attributed respectively to Paranthropus robustus, Homo erectus and Homo neanderthalensis. Enamel extension rates in each of the three fossil taxa fell within the range of modern humans. Root extension rates in the fossil taxa also fell within modern human ranges but differed in their pattern with either an early or late marked increase in root length. Extension rates in the canine crowns were higher in cuspal enamel than in lateral enamel. Combinations of high or low cuspal enamel extension rates, with either longer or shorter times taken to form lateral enamel, explain how crown formation times may vary independently of completed crown heights. [ABSTRACT FROM AUTHOR]

Early hominins formed large and thick-enamelled cheek-teeth within relatively short growth periods as compared with modern humans. To understand better the developmental basis of this process, we measured daily enamel increments, or cross striations, in 17 molars of Plio-Pleistocene hominins representing seven different species, including specimens attributed to early Homo. Our results show considerable variation across species, although all specimens conformed to the known pattern characterised by greater values in outer than inner enamel, and greater cuspal than cervical values. We then compared our results with the megadontia index, which represents tooth size in relation to body mass, for each species to assess the effect of daily growth rates on tooth size. Our results indicate that larger toothed (megadont) taxa display higher rates or faster forming enamel than smaller toothed hominins. By forming enamel quickly, large tooth crowns were able to develop within the constraints of shorter growth periods. Besides daily increments, many animals express long-period markings (striae of Retzius) in their enamel. We report periodicity values (number of cross striations between adjacent striae) in 14 new specimens of Australopithecus afarensis, Paranthropus aethiopicus, Paranthropus boisei, Homo habilis, Homo rudolfensis and Homo erectus, and show that long-period striae express a strong association with male and average male–female body mass. Our results for Plio-Pleistocene hominins show that the biological rhythms that give rise to long-period striae are encompassed within the range of variation known for modern humans, but show a lower mean and modal value of 7 days in australopithecines. In our sample of early Homo, mean and modal periodicity values were 8 days, and therefore similar to modern humans. These new data on daily rates of enamel formation and periodicity provide a better framework to interpret surface manifestations of internal growth markings on fossil hominin tooth crowns. Importantly, our data on early hominin cross striation variation may now contribute towards solving difficult taxonomic diagnoses where much may depend on fragmentary molar remains and enamel structure. [ABSTRACT FROM AUTHOR]

In Primates, enamel thickness variation stems from an evolutionary interplay between functional/adaptive constraints (ecology) and the strict control mechanisms of the morphogenetic program. Most studies on primate enamel thickness have primarily considered the permanent teeth, while the extent of covariation in tooth enamel thickness distribution between deciduous and permanent counterparts remains poorly investigated. In this test study on nine extant and fossil hominids we investigated the degree of covariation in enamel proportions between 25 pairs of mandibular dm2 and M1 by a so-called “lateral enamel thickness diphyodontic index”. The results did not provide an unambiguous picture, but rather suggest complex patterns likely resulting from the influence of many interactive factors. Future research should test the congruence of the “diphyodontic signal” between the anterior and the postcanine dentition, as well as between enamel and the enamel-dentine junction topography. [ABSTRACT FROM AUTHOR]

Recent studies have provided great insight into hominin life history evolution by utilizing incremental lines found in dental tissues to reconstruct and compare the growth records of extant and extinct humans versus other ape taxa. Among the hominins, studies that have examined Retzius periodicity (RP) variation have come to contradictory conclusions in some instances. To clarify RP variation among hominins and better place this variation in its broader evolutionary context, we conduct the most comprehensive analysis of published RP values for hominins and great apes to date. We gathered all available data from the literature on RP data from extant humans, great apes, and fossil hominins and assessed their variation using parametric and nonparametric analyses of variance. We also performed phylogenetic generalized least-squares regressions of RP data for these taxa as well as a larger set of hominoids for which RP data have been published against data for body mass, encephalization, and mean semicircular canal radius (a proxy for metabolic rate). Our results show that modern humans have a mean RP significantly differing from that of other hominins. Pongo also is significantly different from nearly all other taxa in all analyses. Our results also demonstrate that RP variation among hominins scales with respect to body mass, encephalization, and semicircular canal radius similarly to other hominids but that modern humans and Pongo stand out in this regard. Operating within the hypothesis that RP reflects autonomic biorhythms that regulate multiple life history variables, our results reinforce the idea that Homo sapiens has evolved a life history distinct from other hominins, even from other members of Homo, and suggest that many of these life history differences may be driven by hypothalamic output from the brain. [ABSTRACT FROM AUTHOR]