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, 10 (11), e0141614
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Unique Dental Morphology of Homo Floresiensis and Its Evolutionary Implications

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Unique Dental Morphology of Homo Floresiensis and Its Evolutionary Implications

Yousuke Kaifu et al. PLoS One.

Abstract

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.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Teeth of Homo floresiensis.
Right (A) and left (B) anterior dentitions of the LB1 mandible. (C) Maxillary dentition of LB1 with EDJ surface images for the right P3 and P4. (D) Mandibular molars of LB1. (E) Occlusal (left) and lingual (right) views of the LB2/2 left P3. (F) Occlusal view of the LB15/1 right P4. Left (G) and right (H) anterior dentitions of the LB6/1 mandible with a photograph of a cast of its left C1 (with blue background). (I) Mandibular molars of LB6/1. See ref. [24] for LB 15/2 (I1) and LB6/14 (I1).
Fig 2
Fig 2. Z-scores for the tooth crown length (MD) and breadth (LL or BL) for H. floresiensis and other fossil Homo groups as compared to the global H. sapiens sample.
Z-scores are relative deviations from the H. sapiens means in units of standard deviation. Note that the Dmanisi Homo sample here is based on the two smaller individuals. Due to sever tooth wear the largest individual (D4500/2600) l was excluded [27].
Fig 3
Fig 3. Results of the PCAs based on size-adjusted MD and BL crown diameters.
Analyses of the maxillary (A) and mandibular (B) teeth. Black letters = H. sapiens subsample means (P = prehistoric Southeast Asia, N = Philippine Negrito, G = New Guinea, A = Australia/Tasmania Aborigine, I = modern Indonesian, b = Bushman, p = African Pygmy, e = East African, g = German); Gray crosses = H. sapiens individuals; Colored letters = archaic Homo individuals (L1 = LB1, L6 = LB6/1, S = early Javanese H. erectus [Sangiran 4, 22], D = Dmanisi [D2282/211, 2700/2735], e = H. ergaster [KNM-ER 992], h = H. habilis [L894-1; Omo75-14G; KNM-ER 1590, 1802, 1813, 60000; OH 13, 16, 39]).
Fig 4
Fig 4. Plots of PC scores derived from the normalized Elliptic Fourier Analyses (EFAs) on the crown contours (mandibular premolars).
(A) and (B) Mandibular first premolar. (C) and (D) Mandibular second premolar. Symbol and color codes: gray symbols = H. sapiens (crosses = Southeast Asia/Melanesia/Australia, circles = African Pygmy); colored letters = fossil Homo (L1 = LB1, L2 = LB2/2, L6 = LB6/1, L15 = LB15/1, S = early Javanese H. erectus (Sangiran Lower), s = early Javanese H. erectus (Sangiran Upper), D = Dmanisi, e = H. ergaster, h = H. habilis). The right and left teeth are included for H. floresiensis when available and they are indicated by the dashed line with arrow heads. The crown outlines for -2 SD, 0, and +2 SD, 95% confidence ellipses for the H. sapiens sample, and ranges for H. erectus and H. habilis samples are shown. Proportion of the variance explained by each PC is in the parentheses.
Fig 5
Fig 5. Plots of PC scores derived from the normalized Elliptic Fourier Analyses (EFAs) on the crown contours (maxillary molars).
(A) and (B) Maxillary first molar. (C) and (D) Maxillary second molar. See Fig 4 for notes.
Fig 6
Fig 6. Plots of PC scores derived from the normalized Elliptic Fourier Analyses (EFAs) on the crown contours (mandibular molars).
(A) and (B) Mandibular first molar. (C) and (D) Mandibular second molar. See Fig 4 for notes.
Fig 7
Fig 7. Relationships between tooth crown size and selected morphological traits.
(A) C1 crown shape. (B) and (C) M1 crown shape. (D) and (E) Mandibular molar size proportions. The ‘crown size’ is square root of the computed crown area (MD × BL diameters).
Fig 8
Fig 8. Six PCs showing significant differences in crown contours between H. habilis and early Javanese H. erectus.
The positive and negative are reversed from Figs 4, 5 and 6 in PC3 for P4, PC1 for M1, and PC1 for M1, for the sake of unanimity in the directions of variation. See Figs 4, 5 and 6 for component loading for each PC. The shape variation reflected by each PC is shown in the upper row. Blue and red lines indicate contours of +2 SD and −2 SD of the entire sample, respectively. The green line is the grand mean. In all of these six cases, the contours of H. floresiensis are close to the red outlines, and those of H. habilis to blue outlines. Box plots of the PC scores are shown in the lower row. Note that H. habilis plots far from H. floresiensis whereas early Javanese H. erectus is closer to H. floresiensis in all these PCs.
Fig 9
Fig 9. Dentitions of H. floresiensis and selected Early Pleistocene Homo specimens.
Maxillary (A) and mandibular (B) dentitions of H. floresiensis (LB), early Javanese H. erectus (Sangiran), and H. habilis (KNM-ER and OH).

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Grant support

This work was supported by funding from the Japan Society for the Promotion of Science (https://www.jsps.go.jp/english/), No. 24247044, YK; National Museum of Nature and Science, YK. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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