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Post by Admin on Jan 30, 2018 18:38:40 GMT
When the skull of the child was first discovered, it raised more questions than answers. Although it was nearly 50,000 years old, unearthed deep within the Sidrón limestone caves of Asturias, Spain, it could easily be mistaken for that of a modern-day youth. The archaeologists who later examined it wanted to know: What was the story of this young Neanderthal? And how similar was he to today’s young Homo sapiens? As the skeleton’s additional bones began coming to light one by one, the picture came into focus. “When the first remains of the juvenile skeleton started to appear,” says Luis Rios, a paleontologist at Madrid’s Museo Nacional de Ciencias Naturales and a coauthor on a just-published study in the journal Science, “we realized that it was a very interesting skeleton.” The reason the skeleton was so compelling to researchers was twofold. First, as a child skeleton, the specimen offered a window into how Neanderthals grew and developed into adults, which researchers could then compare against modern Homo sapiens. Second, the unusually pristine condition of the jawbone and teeth made it possible to draw a precise estimate of the juvenile’s age at the time of death.
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Post by Admin on Jan 31, 2018 18:53:07 GMT
“Dental development is very important in human evolution and in primates,” said Antonio Rosas, the museum’s chair of paleoanthropology and lead author on the study, during a press conference on Wednesday. “And also in establishing the chronological age—that is, the age of the individual in years or days and months, or in an absolute time.” Through an analysis of naturally occurring markings on the juvenile’s first left upper molar, Rosas and his coauthors concluded that the child had almost certainly died between the ages of 7.61 and 7.78 years. While DNA testing was inconclusive, canine tooth size and general bone robustness indicate that he was also male. Further findings, Rosas says, suggest that humans may not be as distinct from Neanderthals as we often tell ourselves—with two key exceptions. It was over 23 years ago that a band of spelunkers in northern Spain chanced upon a cache of Neanderthal skeletons, 13 in all, in a part of the Sidrón cave complex now known as the Galería del Osario: the Tunnel of Bones. Comprising several adult males, several adolescent males, several adult females and several infants, the 49,000-year-old collection whetted the appetites of evolutionary scientists worldwide. By now, 2,500 distinct bones have been unearthed in the region—an incredible windfall for the international scientific community. The team performed a full examination of the skeleton in order to contrast the stages of growth in the Neanderthal child with the equivalent stages of growth in Homo sapiens. What they found was that the Neanderthal was nearly indistinguishable from Homo sapiens in the degree to which its bones had developed. From hands to knees, says Rosas, “the general pattern of growth is very similar to that of modern humans.”
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Post by Admin on Feb 2, 2018 4:52:53 GMT
However, his team did observe two important points of divergence—which could lend insight into how Neanderthals developed and aged. The first was in the spinal column. CT scans of the Neanderthal’s spine revealed that certain vertebrae in the boy’s backbone had not yet fused; those of a modern human child would have fused by age 5 or 6. Second, inspection of the cranium—which houses the brain—implied that brain development in Neanderthals may have been a slightly more protracted process than in Homo sapiens. The endocranial volume of the specimen was about 87.5 percent of the average adult Neanderthal’s, the team reports. By contrast, for a modern 7-year-old human, the brain is typically 95 percent of the way to its adult size. Neandertal growth patterns The ontogeny of different parts of the Neandertal skeleton has been derived from isolated bones and fragments. Rosas et al. present a more complete skeleton of a Neandertal child, aged 7 to 8 years, from a 49,000-year-old site in northern Spain. The skeleton preserves dental, cranial, and postcranial material, allowing the assessment of dental and skeletal maturation with age. Most of the elements indicate an overall growth rate similar to that of modern human children. The main difference between Neandertals and modern humans is in the vertebral column. Also, several features indicate ongoing brain growth. The pattern of vertebral maturation and extended brain growth might reflect the broad Neandertal body form and physiology, rather than a fundamental difference in the overall pace of growth in Neandertals. Science, this issue p. 1282 Abstract Ontogenetic studies help us understand the processes of evolutionary change. Previous studies on Neandertals have focused mainly on dental development and inferred an accelerated pace of general growth. We report on a juvenile partial skeleton (El Sidrón J1) preserving cranio-dental and postcranial remains. We used dental histology to estimate the age at death to be 7.7 years. Maturation of most elements fell within the expected range of modern humans at this age. The exceptions were the atlas and mid-thoracic vertebrae, which remained at the 5- to 6-year stage of development. Furthermore, endocranial features suggest that brain growth was not yet completed. The vertebral maturation pattern and extended brain growth most likely reflect Neandertal physiology and ontogenetic energy constraints rather than any fundamental difference in the overall pace of growth in this extinct human.
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Post by Admin on Feb 7, 2018 18:58:56 GMT
Neandertals provide us with an important perspective on our own biology (1). Both modern humans and Neandertals arose from a recent common ancestor along independent evolutionary lines, becoming large-brained hominins but with contrasting body forms. Developing a large brain is energetically expensive and places a constraint on somatic growth (2). The unusually high cost of modern human brain development is greatest during the infant and childhood periods and seems to require a compensatory slowing of childhood body growth (2, 3). Neandertals had larger average cranial capacity than modern humans, but little is known about the ontogenetic trajectories of brain and body underlying this difference. Some studies have proposed that a larger brain in Neandertals can be explained by a faster rate of early postnatal growth (4), yet others have proposed a longer period of growth as an explanation (5, 6). However, in large-brained hominins like modern humans and Neandertals, an accelerated pace of brain growth, coincident with accelerated somatic growth, would impose a high energetic cost (2). Yet the trade-off between the different aspects of somatic and neural growth in Neandertals, particularly during the juvenile period, remains unclear. Here we describe a partial juvenile Neandertal skeleton from the 49-thousand-year-old site of El Sidrón (Asturias, Spain). The specimen has a mixed dentition of deciduous and permanent teeth and preserves cranial, dental, and postcranial remains (Figs. 1 and 2A and supplementary text 1 and 2), providing a rare opportunity to estimate an age at death from daily dental incremental markings preserved in teeth, against which to compare many aspects of its dento-skeletal maturation. Chronological age is fundamental for assessing patterns of maturation in different dento-skeletal systems, both within individuals and between species. This approach allowed us to ask what the probability is that this specimen would fit within or lie beyond the ranges of modern human variation and represent its own pattern of dental and skeletal maturation.
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Post by Admin on Feb 8, 2018 18:44:00 GMT
Fig. 1 El Sidrón J1 Neandertal skeleton The El Sidrón cave system (Asturias, Spain) (Fig. 1C and supplementary text 1) has provided more than 2500 remains of seven adults and six immature individuals belonging to a single Neandertal group (7) with close kinship relations (8). Among them, a partial immature skeleton was recovered with up to ~36% (left side) preserved. Virtually all of the remains associated with this individual come from the 1-m2 G-6 square grid of the archaeological site (supplementary text 2), and importantly, several were found in anatomical association. From the three mitochondrial DNA lineages detected within this Neandertal group, this individual belongs to line C of the group and was tentatively identified as the child of adult female 4 and the older sibling of infant 1 (8). A number of diagnostic Neandertal features are present throughout the skeleton (supplementary text 2). Although ancient DNA failed to confirm the sex, group-specific evaluation of canine size and bone robusticity strongly suggests that it was male (supplementary text 2). Dental development, with a near-complete first molar (M1) root, would place him in the juvenile stage of hominin life history (3). Height and weight estimates indicate that he was a sturdy individual, weighing ~26 kg and standing ~111 cm tall at the time of death (supplementary text 2). Biosocial markers indicate that El Sidrón juvenile 1 (J1) was right-handed, with evidence that he was involved with, or learning, adult behaviors and economic activities (9). Apart from mild linear dental enamel hypoplasia around the age of 2 to 3 years, there is no other evidence of pathology. Several postmortem cut marks appear on some of the bones. Age at death was first established by dental histology. Daily incremental markings in two sections of El Sidrón J1 first left upper molar (see materials and methods, figs. S1 and S2, and supplementary text 3) were used to estimate an average age at death of 7.69 years (range: 7.61 to 7.78 years). Biological maturity was then assessed using modern human references for dental, skeletal, and somatic maturation (supplementary text 4 to 7). Fig. 2 Dental and vertebral maturation of El Sidrón J1. (A) Computed tomography (CT) scan image of the mandible of El Sidrón J1, with the enamel shown in green. (B) Probability density plots (PDPs) for mean age of transition entering each mandibular tooth stage scored for El Sidrón J1 in a radiographic sample (n = 6829 individuals) of modern children of known chronological age (CA). Red vertical lines represent the CA of El Sidrón J1 from dental histology (7.69 years; range: 7.61 to 7.78 years). (C) Maturation of the spine relative to CA in El Sidrón J1 and modern humans. The vertical axis represents the presacral vertebral column; the horizontal axis represents age in years. For each vertebra, the three successive maturation stages are represented (see vertebral diagrams in the figure): stage one, unfused posterior synchondrosis (PS) and neurocentral synchondrosis (AS); stage two, fused PS and unfused neurocentral synchondrosis (NS); stage three, fused PS and NS. A sample of 70 known CA skeletons was used to develop PDPs for mean age of transition entering fusion of the NS for each vertebra (from stage two to three). El Sidrón J1 is displayed in red, and the two oldest modern human cases (4.83 and 5.6 years) with a spine maturation similar to that of El Sidrón J1 (unfused C1 and middle thoracic vertebrae) are represented in black. The C1 falls within the P = 0.01 shaded area of the PDP, whereas the thoracic vertebrae would fall outside (T3 and T4), in the P = 0.05 shaded area (T5, T6, T7, and T9), or under the PDP (T8). (D) Maturation of the spine relative to dental maturation in El Sidrón J1 and in modern humans. The vertical axis represents C1 and the thoracic vertebrae, whereas stages of formation of the first permanent mandibular molar are represented on the horizontal axis. A sample of 106 modern human skeletons of diverse origins was used to develop PDPs for mean first molar formation stage entering fusion of the NS for each vertebra (from stage two to three). The vertical red line, representing complete root formation of the first permanent molar of El Sidrón J1, falls in the P = 0.05 area in all PDPs.
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