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Dental ontogeny in pliocene and early pleistocene hominins.

Smith TM, Tafforeau P, Le Cabec A, Bonnin A, Houssaye A, Pouech J, Moggi-Cecchi J, Manthi F, Ward C, Makaremi M, Menter CG - PLoS ONE (2015)

Bottom Line: Long-period line periodicities range from at least 6-12 days (possibly 5-13 days), and do not support the hypothesis that australopiths have lower mean values than extant or fossil Homo.Extant human standards overestimate age at death in hominins predating Homo sapiens, and should not be applied to other fossil taxa.We urge caution when inferring life history as aspects of dental development in Pliocene and early Pleistocene fossils are distinct from modern humans and African apes, and recent work has challenged the predictive power of primate-wide associations between hominoid first molar emergence and certain life history variables.

View Article: PubMed Central - PubMed

Affiliation: Department of Human Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America.

ABSTRACT
Until recently, our understanding of the evolution of human growth and development derived from studies of fossil juveniles that employed extant populations for both age determination and comparison. This circular approach has led to considerable debate about the human-like and ape-like affinities of fossil hominins. Teeth are invaluable for understanding maturation as age at death can be directly assessed from dental microstructure, and dental development has been shown to correlate with life history across primates broadly. We employ non-destructive synchrotron imaging to characterize incremental development, molar emergence, and age at death in more than 20 Australopithecus anamensis, Australopithecus africanus, Paranthropus robustus and South African early Homo juveniles. Long-period line periodicities range from at least 6-12 days (possibly 5-13 days), and do not support the hypothesis that australopiths have lower mean values than extant or fossil Homo. Crown formation times of australopith and early Homo postcanine teeth fall below or at the low end of extant human values; Paranthropus robustus dentitions have the shortest formation times. Pliocene and early Pleistocene hominins show remarkable variation, and previous reports of age at death that employ a narrow range of estimated long-period line periodicities, cuspal enamel thicknesses, or initiation ages are likely to be in error. New chronological ages for SK 62 and StW 151 are several months younger than previous histological estimates, while Sts 24 is more than one year older. Extant human standards overestimate age at death in hominins predating Homo sapiens, and should not be applied to other fossil taxa. We urge caution when inferring life history as aspects of dental development in Pliocene and early Pleistocene fossils are distinct from modern humans and African apes, and recent work has challenged the predictive power of primate-wide associations between hominoid first molar emergence and certain life history variables.

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Ages predicted from extant human molar calcification standards compared to known- or histologically-derived ages.Two values are presented for A. anamensis KNM-KP 34725 due to uncertainty in the periodicity value. Data on extant human children derive from panoramic X-rays of known-age European and North African children, representing an expanded sample originally detailed in [54]. Fossil Homo sapiens and Homo neanderthalensis samples are from [54]; Pan troglodytes are known-age wild western chimpanzees [72].
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pone.0118118.g004: Ages predicted from extant human molar calcification standards compared to known- or histologically-derived ages.Two values are presented for A. anamensis KNM-KP 34725 due to uncertainty in the periodicity value. Data on extant human children derive from panoramic X-rays of known-age European and North African children, representing an expanded sample originally detailed in [54]. Fossil Homo sapiens and Homo neanderthalensis samples are from [54]; Pan troglodytes are known-age wild western chimpanzees [72].

Mentions: Since our age at death estimates do not rely on extant human or great ape developmental information, we compared ages derived from the calcification stage of each tooth of each individual (Figs. C-R in S1 File) to a sample of known-age extant humans and wild chimpanzees (Fig. S in S1 File). Because chimpanzee anterior tooth and premolar morphology differs markedly from fossil hominins and extant humans, we also assessed the developmental status of individuals based solely on molar calcification (Fig. 4). Pliocene and early Pleistocene hominins followed an ontogenetic schedule of molar development that is more similar to chimpanzees than to extant humans, as has been inferred from assessments of other Pliocene and early Pleistocene hominins [14, 15, 20, 45]. However, marked differences are apparent for one A. anamensis (KNM-KP 34725) and one A. africanus individual (MLD 11/30), which show particularly rapid dental development that exceeds similarly-aged humans and chimpanzees. Age at death was also predicted for two P. robustus individuals with captive chimpanzee standards [79]. The resulting age estimates were closer to the actual histological ages than the ages predicted from extant human standards for only one of two cases (Table F in S1 File). In summary, radiographic developmental standards from extant humans and chimpanzees do not yield consistent or accurate ages at death estimates for Pliocene or early Pleistocene hominins.


Dental ontogeny in pliocene and early pleistocene hominins.

Smith TM, Tafforeau P, Le Cabec A, Bonnin A, Houssaye A, Pouech J, Moggi-Cecchi J, Manthi F, Ward C, Makaremi M, Menter CG - PLoS ONE (2015)

Ages predicted from extant human molar calcification standards compared to known- or histologically-derived ages.Two values are presented for A. anamensis KNM-KP 34725 due to uncertainty in the periodicity value. Data on extant human children derive from panoramic X-rays of known-age European and North African children, representing an expanded sample originally detailed in [54]. Fossil Homo sapiens and Homo neanderthalensis samples are from [54]; Pan troglodytes are known-age wild western chimpanzees [72].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4334485&req=5

pone.0118118.g004: Ages predicted from extant human molar calcification standards compared to known- or histologically-derived ages.Two values are presented for A. anamensis KNM-KP 34725 due to uncertainty in the periodicity value. Data on extant human children derive from panoramic X-rays of known-age European and North African children, representing an expanded sample originally detailed in [54]. Fossil Homo sapiens and Homo neanderthalensis samples are from [54]; Pan troglodytes are known-age wild western chimpanzees [72].
Mentions: Since our age at death estimates do not rely on extant human or great ape developmental information, we compared ages derived from the calcification stage of each tooth of each individual (Figs. C-R in S1 File) to a sample of known-age extant humans and wild chimpanzees (Fig. S in S1 File). Because chimpanzee anterior tooth and premolar morphology differs markedly from fossil hominins and extant humans, we also assessed the developmental status of individuals based solely on molar calcification (Fig. 4). Pliocene and early Pleistocene hominins followed an ontogenetic schedule of molar development that is more similar to chimpanzees than to extant humans, as has been inferred from assessments of other Pliocene and early Pleistocene hominins [14, 15, 20, 45]. However, marked differences are apparent for one A. anamensis (KNM-KP 34725) and one A. africanus individual (MLD 11/30), which show particularly rapid dental development that exceeds similarly-aged humans and chimpanzees. Age at death was also predicted for two P. robustus individuals with captive chimpanzee standards [79]. The resulting age estimates were closer to the actual histological ages than the ages predicted from extant human standards for only one of two cases (Table F in S1 File). In summary, radiographic developmental standards from extant humans and chimpanzees do not yield consistent or accurate ages at death estimates for Pliocene or early Pleistocene hominins.

Bottom Line: Long-period line periodicities range from at least 6-12 days (possibly 5-13 days), and do not support the hypothesis that australopiths have lower mean values than extant or fossil Homo.Extant human standards overestimate age at death in hominins predating Homo sapiens, and should not be applied to other fossil taxa.We urge caution when inferring life history as aspects of dental development in Pliocene and early Pleistocene fossils are distinct from modern humans and African apes, and recent work has challenged the predictive power of primate-wide associations between hominoid first molar emergence and certain life history variables.

View Article: PubMed Central - PubMed

Affiliation: Department of Human Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America.

ABSTRACT
Until recently, our understanding of the evolution of human growth and development derived from studies of fossil juveniles that employed extant populations for both age determination and comparison. This circular approach has led to considerable debate about the human-like and ape-like affinities of fossil hominins. Teeth are invaluable for understanding maturation as age at death can be directly assessed from dental microstructure, and dental development has been shown to correlate with life history across primates broadly. We employ non-destructive synchrotron imaging to characterize incremental development, molar emergence, and age at death in more than 20 Australopithecus anamensis, Australopithecus africanus, Paranthropus robustus and South African early Homo juveniles. Long-period line periodicities range from at least 6-12 days (possibly 5-13 days), and do not support the hypothesis that australopiths have lower mean values than extant or fossil Homo. Crown formation times of australopith and early Homo postcanine teeth fall below or at the low end of extant human values; Paranthropus robustus dentitions have the shortest formation times. Pliocene and early Pleistocene hominins show remarkable variation, and previous reports of age at death that employ a narrow range of estimated long-period line periodicities, cuspal enamel thicknesses, or initiation ages are likely to be in error. New chronological ages for SK 62 and StW 151 are several months younger than previous histological estimates, while Sts 24 is more than one year older. Extant human standards overestimate age at death in hominins predating Homo sapiens, and should not be applied to other fossil taxa. We urge caution when inferring life history as aspects of dental development in Pliocene and early Pleistocene fossils are distinct from modern humans and African apes, and recent work has challenged the predictive power of primate-wide associations between hominoid first molar emergence and certain life history variables.

Show MeSH
Related in: MedlinePlus