Publications by authors named "Reiko T Kono"

15 Publications

  • Page 1 of 1

Metameric variation of upper molars in hominoids and its implications for the diversification of molar morphogenesis.

J Hum Evol 2020 01 27;138:102706. Epub 2019 Nov 27.

The University Museum, The University of Tokyo, Tokyo, Japan.

Metameric variation of molar size is in part associated with the dietary adaptations of mammals and results from slight alterations of developmental processes. Humans and great apes exhibit conspicuous variation in tooth morphology both between taxa and across tooth types. However, the manner in which metameric variation in molars emerged among apes and humans via evolutionary alterations in developmental processes remains largely unknown. In this study, we compare the enamel-dentine junction of the upper molars of humans-which closely correlates with morphology of the outer enamel surface and is less affected by wear-with that of the other extant hominoids: chimpanzees, bonobos, gorillas, orangutans, and gibbons. We used the morphometric mapping method to quantify and visualize three-dimensional morphological variation, and applied multivariate statistical analyses. Results revealed the following: 1) extant hominoids other than humans share a common pattern of metameric variation characterized by a largely linear change in morphospace; this indicates a relatively simple graded change in metameric molar shape; 2) intertaxon morphological differences become less distinct from the mesial to distal molars; and 3) humans diverge from the extant ape pattern in exhibiting a distinct metameric shape change trajectory in the morphospace. The graded shape change and lower intertaxon resolution from the mesial to distal molars are consistent with the concept of a 'key' tooth. The common metameric pattern observed among the extant nonhuman hominoids indicates that developmental patterns underlying metameric variation were largely conserved during ape evolution. Furthermore, the human-specific metameric pattern suggests considerable developmental modifications in the human lineage.
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http://dx.doi.org/10.1016/j.jhevol.2019.102706DOI Listing
January 2020

A mandible from the Middle Pleistocene Hexian site and its significance in relation to the variability of Asian Homo erectus.

Am J Phys Anthropol 2017 04 21;162(4):715-731. Epub 2017 Jan 21.

Department of Anthropology, University College London (UCL), 14 Taviton Street, London, WC1H 0BW.

Objectives: This study presents the first detailed morphological description and comparison of a Middle Pleistocene hominin mandibular fragment (PA 831) and associated teeth from the Hexian site in Eastern China. We aim to investigate where the Hexian mandible fits within the genus Homo variability in the light of an increased and better characterized Asian fossils record.

Methods: Comparative samples include Pleistocene Homo mandibles and teeth from Africa, Asia, and Europe, as well as earlier African hominins (Australopithecus and early Homo) and Holocene recent humans. Both conventional morphological description and metric analysis were used. In addition, virtual reconstructions of the enamel dentine junction (EDJ) surface, pulp cavity, and roots with micro-CT were used to the mandible and teeth.

Results: The Hexian mandible is characterized by a plesiomorphic structural pattern for the Homo clade, with strong corpus robustness and a subparallel and low-positioned mylohyoid line that differentiates the swollen subalveolar planum from the shallow subalveolar fossa. Features that are derived compared to early Homo include a moderately curved dental arcade, a well-developed lateral prominence placed at the M -M level, and multiple mental foramina. The Hexian mandible's complex enamel surface and strong, stout root structure are primitive traits for the Homo clade. Finally, the highly crenulated "dendrite-like" EDJ found in the molars may represent a dental feature specific to the continental Asian Homo erectus, but more data is needed to confirm this.

Conclusions: Mandibular and dental features indicate that the Hexian mandible and teeth differ from northern Chinese H. erectus and European Middle Pleistocene hominins, but show some affinities with the Early Pleistocene specimens from Africa (Homo ergaster) and Java (H. erectus), as well as the Middle-Late Pleistocene mandible from Penghu, Taiwan. Compared to contemporaneous continental Asian hominin populations, the Hexian fossils may represent the survival of a primitive hominin, with more primitive morphologies than other contemporaneous or some chronologically older Asian hominin specimens.
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http://dx.doi.org/10.1002/ajpa.23162DOI Listing
April 2017

Homo floresiensis-like fossils from the early Middle Pleistocene of Flores.

Nature 2016 06;534(7606):245-8

Centre for Archaeological Science, School of Earth &Environmental Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia.

The evolutionary origin of Homo floresiensis, a diminutive hominin species previously known only by skeletal remains from Liang Bua in western Flores, Indonesia, has been intensively debated. It is a matter of controversy whether this primitive form, dated to the Late Pleistocene, evolved from early Asian Homo erectus and represents a unique and striking case of evolutionary reversal in hominin body and brain size within an insular environment. The alternative hypothesis is that H. floresiensis derived from an older, smaller-brained member of our genus, such as Homo habilis, or perhaps even late Australopithecus, signalling a hitherto undocumented dispersal of hominins from Africa into eastern Asia by two million years ago (2 Ma). Here we describe hominin fossils excavated in 2014 from an early Middle Pleistocene site (Mata Menge) in the So'a Basin of central Flores. These specimens comprise a mandible fragment and six isolated teeth belonging to at least three small-jawed and small-toothed individuals. Dating to ~0.7 Ma, these fossils now constitute the oldest hominin remains from Flores. The Mata Menge mandible and teeth are similar in dimensions and morphological characteristics to those of H. floresiensis from Liang Bua. The exception is the mandibular first molar, which retains a more primitive condition. Notably, the Mata Menge mandible and molar are even smaller in size than those of the two existing H. floresiensis individuals from Liang Bua. The Mata Menge fossils are derived compared with Australopithecus and H. habilis, and so tend to support the view that H. floresiensis is a dwarfed descendent of early Asian H. erectus. Our findings suggest that hominins on Flores had acquired extremely small body size and other morphological traits specific to H. floresiensis at an unexpectedly early time.
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http://dx.doi.org/10.1038/nature17999DOI Listing
June 2016

Unique Dental Morphology of Homo floresiensis and Its Evolutionary Implications.

PLoS One 2015 18;10(11):e0141614. Epub 2015 Nov 18.

Centre for Archaeological Science, University of Wollongong, Wollongong, Australia.

Homo floresiensis is an extinct, diminutive hominin species discovered in the Late Pleistocene deposits of Liang Bua cave, Flores, eastern Indonesia. The nature and evolutionary origins of H. floresiensis' unique physical characters have been intensively debated. Based on extensive comparisons using linear metric analyses, crown contour analyses, and other trait-by-trait morphological comparisons, we report here that the dental remains from multiple individuals indicate that H. floresiensis had primitive canine-premolar and advanced molar morphologies, a combination of dental traits unknown in any other hominin species. The primitive aspects are comparable to H. erectus from the Early Pleistocene, whereas some of the molar morphologies are more progressive even compared to those of modern humans. This evidence contradicts the earlier claim of an entirely modern human-like dental morphology of H. floresiensis, while at the same time does not support the hypothesis that H. floresiensis originated from a much older H. habilis or Australopithecus-like small-brained hominin species currently unknown in the Asian fossil record. These results are however consistent with the alternative hypothesis that H. floresiensis derived from an earlier Asian Homo erectus population and experienced substantial body and brain size dwarfism in an isolated insular setting. The dentition of H. floresiensis is not a simple, scaled-down version of earlier hominins.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0141614PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4651360PMC
June 2016

Evolutionary trend in dental size in Gigantopithecus blacki revisited.

J Hum Evol 2015 Jun 17;83:91-100. Epub 2015 Apr 17.

Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China.

Previous analyses of dental size in Gigantopithecus blacki indicated marked sexual dimorphism and a trend towards increasing size through time. These studies were based on a sample of over 700 teeth from five localities excavated prior to 1990. Since then, 12 additional cave sites have been discovered in southern China, yielding hundreds of isolated teeth of G. blacki. Most of these sites are well dated by a combination of biochronology and absolute dating methods, so we now have a much better understanding of the chronology of G. blacki. Here, we reexamine the degree of sexual dimorphism and the question of dental size increase through time in G. blacki based on the expanded collections now available. Our results show that sexual dimorphism is not as marked as indicated in previous studies and confirm earlier analyses suggesting that the postcanine teeth of G. blacki tend to become larger through time from the beginning of the Early Pleistocene to the Middle Pleistocene.
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http://dx.doi.org/10.1016/j.jhevol.2015.03.005DOI Listing
June 2015

The first archaic Homo from Taiwan.

Nat Commun 2015 Jan 27;6:6037. Epub 2015 Jan 27.

Department of Life Science, Tunghai University, 0704 PO Box 988, No. 181, Sector 3, Taichung Port Road, Taichung 40704, Taiwan.

Recent studies of an increasing number of hominin fossils highlight regional and chronological diversities of archaic Homo in the Pleistocene of eastern Asia. However, such a realization is still based on limited geographical occurrences mainly from Indonesia, China and Russian Altai. Here we describe a newly discovered archaic Homo mandible from Taiwan (Penghu 1), which further increases the diversity of Pleistocene Asian hominins. Penghu 1 revealed an unexpectedly late survival (younger than 450 but most likely 190-10 thousand years ago) of robust, apparently primitive dentognathic morphology in the periphery of the continent, which is unknown among the penecontemporaneous fossil records from other regions of Asia except for the mid-Middle Pleistocene Homo from Hexian, Eastern China. Such patterns of geographic trait distribution cannot be simply explained by clinal geographic variation of Homo erectus between northern China and Java, and suggests survival of multiple evolutionary lineages among archaic hominins before the arrival of modern humans in the region.
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http://dx.doi.org/10.1038/ncomms7037DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4316746PMC
January 2015

Possible change in dental morphology in Gigantopithecus blacki just prior to its extinction: evidence from the upper premolar enamel-dentine junction.

J Hum Evol 2014 Oct 23;75:166-71. Epub 2014 Jul 23.

Center for the Study of Human Origins, Department of Anthropology, New York University, New York, NY 10003, USA.

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http://dx.doi.org/10.1016/j.jhevol.2014.06.010DOI Listing
October 2014

Brain size of Homo floresiensis and its evolutionary implications.

Proc Biol Sci 2013 Jun 17;280(1760):20130338. Epub 2013 Apr 17.

Department of Biological Sciences, The University of Tokyo, , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.

The extremely small endocranial volume (ECV) of LB1, the type specimen of Homo floresiensis, poses a challenge in our understanding of human brain evolution. Some researchers hypothesize dramatic dwarfing of relative brain size from Homo erectus presumably without significant decrease in intellectual function, whereas others expect a lesser degree of brain diminution from a more primitive, small-brained form of hominin currently undocumented in eastern Asia. However, inconsistency in the published ECVs for LB1 (380-430 cc), unclear human intraspecific brain-body size scaling and other uncertainties have hampered elaborative modelling of its brain size reduction. In this study, we accurately determine the ECV of LB1 using high-resolution micro-CT scan. The ECV of LB1 thus measured, 426 cc, is larger than the commonly cited figure in previous studies (400 cc). Coupled with brain-body size correlation in Homo sapiens calculated based on a sample from 20 worldwide modern human populations, we construct new models of the brain size reduction in the evolution of H. floresiensis. The results show a more significant contribution of scaling effect than previously claimed.
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http://dx.doi.org/10.1098/rspb.2013.0338DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3652458PMC
June 2013

Paleobiological implications of the Ardipithecus ramidus dentition.

Science 2009 Oct;326(5949):94-9

University Museum, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan.

The Middle Awash Ardipithecus ramidus sample comprises over 145 teeth, including associated maxillary and mandibular sets. These help reveal the earliest stages of human evolution. Ar. ramidus lacks the postcanine megadontia of Australopithecus. Its molars have thinner enamel and are functionally less durable than those of Australopithecus but lack the derived Pan pattern of thin occlusal enamel associated with ripe-fruit frugivory. The Ar. ramidus dental morphology and wear pattern are consistent with a partially terrestrial, omnivorous/frugivorous niche. Analyses show that the ARA-VP-6/500 skeleton is female and that Ar. ramidus was nearly monomorphic in canine size and shape. The canine/lower third premolar complex indicates a reduction of canine size and honing capacity early in hominid evolution, possibly driven by selection targeted on the male upper canine.
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October 2009

The Ardipithecus ramidus skull and its implications for hominid origins.

Science 2009 Oct;326(5949):68e1-7

University Museum, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.

The highly fragmented and distorted skull of the adult skeleton ARA-VP-6/500 includes most of the dentition and preserves substantial parts of the face, vault, and base. Anatomical comparisons and micro-computed tomography-based analysis of this and other remains reveal pre-Australopithecus hominid craniofacial morphology and structure. The Ardipithecus ramidus skull exhibits a small endocranial capacity (300 to 350 cubic centimeters), small cranial size relative to body size, considerable midfacial projection, and a lack of modern African ape-like extreme lower facial prognathism. Its short posterior cranial base differs from that of both Pan troglodytes and P. paniscus. Ar. ramidus lacks the broad, anteriorly situated zygomaxillary facial skeleton developed in later Australopithecus. This combination of features is apparently shared by Sahelanthropus, showing that the Mio-Pliocene hominid cranium differed substantially from those of both extant apes and Australopithecus.
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October 2009

A new species of great ape from the late Miocene epoch in Ethiopia.

Nature 2007 Aug;448(7156):921-4

The University Museum, the University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.

With the discovery of Ardipithecus, Orrorin and Sahelanthropus, our knowledge of hominid evolution before the emergence of Pliocene species of Australopithecus has significantly increased, extending the hominid fossil record back to at least 6 million years (Myr) ago. However, because of the dearth of fossil hominoid remains in sub-Saharan Africa spanning the period 12-7 Myr ago, nothing is known of the actual timing and mode of divergence of the African ape and hominid lineages. Most genomic-based studies suggest a late divergence date-5-6 Myr ago and 6-8 Myr ago for the human-chimp and human-gorilla splits, respectively-and some palaeontological and molecular analyses hypothesize a Eurasian origin of the African ape and hominid clade. We report here the discovery and recognition of a new species of great ape, Chororapithecus abyssinicus, from the 10-10.5-Myr-old deposits of the Chorora Formation at the southern margin of the Afar rift. To the best of our knowledge, these are the first fossils of a large-bodied Miocene ape from the African continent north of Kenya. They exhibit a gorilla-sized dentition that combines distinct shearing crests with thick enamel on its 'functional' side cusps. Visualization of the enamel-dentine junction by micro-computed tomography reveals shearing crest features that partly resemble the modern gorilla condition. These features represent genetically based structural modifications probably associated with an initial adaptation to a comparatively fibrous diet. The relatively flat cuspal enamel-dentine junction and thick enamel, however, suggest a concurrent adaptation to hard and/or abrasive food items. The combined evidence suggests that Chororapithecus may be a basal member of the gorilla clade, and that the latter exhibited some amount of adaptive and phyletic diversity at around 10-11 Myr ago.
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http://dx.doi.org/10.1038/nature06113DOI Listing
August 2007

Asa Issie, Aramis and the origin of Australopithecus.

Nature 2006 Apr;440(7086):883-9

Human Evolution Research Center, Museum of Vertebrate Zoology, 3101 Valley Life Sciences Building, University of California at Berkeley, Berkeley, California 94720, USA.

The origin of Australopithecus, the genus widely interpreted as ancestral to Homo, is a central problem in human evolutionary studies. Australopithecus species differ markedly from extant African apes and candidate ancestral hominids such as Ardipithecus, Orrorin and Sahelanthropus. The earliest described Australopithecus species is Au. anamensis, the probable chronospecies ancestor of Au. afarensis. Here we describe newly discovered fossils from the Middle Awash study area that extend the known Au. anamensis range into northeastern Ethiopia. The new fossils are from chronometrically controlled stratigraphic sequences and date to about 4.1-4.2 million years ago. They include diagnostic craniodental remains, the largest hominid canine yet recovered, and the earliest Australopithecus femur. These new fossils are sampled from a woodland context. Temporal and anatomical intermediacy between Ar. ramidus and Au. afarensis suggest a relatively rapid shift from Ardipithecus to Australopithecus in this region of Africa, involving either replacement or accelerated phyletic evolution.
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http://dx.doi.org/10.1038/nature04629DOI Listing
April 2006

Genetics and the evolution of primate enamel thickness: a baboon model.

Am J Phys Anthropol 2004 Jul;124(3):223-33

Department of Anthropology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.

The thickness of mammalian tooth enamel plays a prominent role in paleontology because it correlates with diet, and thicker enamel protects against tooth breakage and wear. Hominid evolutionary studies have stressed the importance of this character for over 30 years, from the identification of "Ramapithecus" as an early Miocene hominid, to the recent discovery that the earliest hominids display molar enamel intermediate in thickness between extant chimpanzees and Australopithecus. Enamel thickness remains largely unexplored for nonhominoid primate fossils, though there is significant variation across modern species. Despite the importance of enamel thickness variation to primate evolution, the mechanisms underlying variation in this trait have not yet been elucidated. We report here on the first quantitative genetic analysis of primate enamel thickness, an analysis based on 506 pedigreed baboons from a captive breeding colony. Computed tomography analysis of 44 Papio mandibular molars shows a zone of sufficiently uniform enamel thickness on the lateral surface of the protoconid. With this knowledge, we developed a caliper metric measurement protocol for use on baboon molars worn to within this zone, enabling the collection of a data set large enough for genetic analyses. Quantitative genetic analyses show that a significant portion of the phenotypic variance in enamel thickness is due to the additive effects of genes and is independent of sex and tooth size. Our models predict that enamel thickness could rapidly track dietary adaptive shifts through geological time, thus increasing the potential for homoplasy in this character. These results have implications for analyses of hominoid enamel thickness variation, and provide a foundation from which to explore the evolution of this phenotype in the papionin fossil record.
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http://dx.doi.org/10.1002/ajpa.10353DOI Listing
July 2004

Homo erectus calvarium from the Pleistocene of Java.

Science 2003 Feb;299(5611):1384-8

Department of Anthropology, National Science Museum, Hyakunincho, Shinjuku-ku, Tokyo 169-0073, Japan.

A Homo erectus calvarium [Sambungmacan 4 (Sm 4)] was recovered from Pleistocene sediments at Sambungmacan in central Java. Micro-computed tomography analysis shows a modern human-like cranial base flexion associated with a low platycephalic vault, implying that the evolution of human cranial globularity was independent of cranial base flexion. The overall morphology of Sm 4 is intermediate between that of earlier and later Javanese Homo erectus; apparent morphological specializations are more strongly expressed in the latter. This supports the hypothesis that later Pleistocene Javanese populations were substantially isolated and made minimal contributions to the ancestry of modern humans.
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http://dx.doi.org/10.1126/science.1081676DOI Listing
February 2003

A three-dimensional analysis of enamel distribution patterns in human permanent first molars.

Arch Oral Biol 2002 Dec;47(12):867-75

Department of Anthropology, National Science Museum, Hyakunincho, Shinjuku-ku, Tokyo 169-0073, Japan.

The morphology of the enamel cap and the thickness of the enamel of human molars are regarded as closely related to function. Previously, enamel thickness has been studied in specific sections only, not the distribution patterns of the entire crown. Here, the three-dimensional distribution pattern of the enamel of human permanent first molars was examined with a newly developed system. A distinctive pattern of enamel thickness common to all the individuals examined was found, regardless of the variation in absolute enamel thickness among individuals. It was confirmed that the lingual faces of upper molars and the buccal faces of lower molars have thicker enamel than the other crown faces. Moreover, in lower molars, enamel was significantly thicker at the hypoconid than at the protoconid crown face. The distal face tended to exhibit thicker enamel than either mesial or lingual faces, owing to the thicker hypoconulid enamel. It is suggested that the gradients of thickness within a molar are not necessarily manifested according to direction, but are the result of cusp-specific patterning. The distribution of enamel in the occlusal fovea was found to correspond to the morphology of the outer enamel surface, with the exception of the distinctly thin enamel at and near the tip of the mesiobuccal cusps in both upper and lower molars. The thickness of the enamel in that region might therefore be related to developmental timing or the topography of the enamel-dentine junction, rather than to functional demand. When viewed from a whole-crown, three-dimensional perspective, enamel thickness patterns are in part, but not entirely, explained as an adaptation to functional demand.
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http://dx.doi.org/10.1016/s0003-9969(02)00151-6DOI Listing
December 2002