The first archaic Homo from Taiwan

Abstract

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.

Figure 1. Map of the major hominin sites mentioned in the text and the submarine topography around the Penghu Channel.

(a) Map of the major hominin sites mentioned in the text. The red pins indicate the occurrence of Crocuta crocuta ultima, and the blue pins Pachycrocuta brevirostris sinensis. The light green areas are the continental shelves 0–100 m below sea level. ‘Hexian etc.’=Hexian, Chaoxian and Tangshan. (b) The submarine topography around the Penghu Channel. The location of vertebrate fossil concentration in the Penghu Channel is encircled. The base map created using the GeoMapApp software (http://www.geomapapp.org/) and Global Multi-Resolution Topography synthesis.

Figure 2. Plot of the relative F and Na contents in the bone samples from Penghu Channel.

Slightly less F/P₂O₅ and slightly greater Na₂O/P₂O₅ contents of Penghu 1 compared with those for the Crocuta samples suggest equal or slightly younger relative age for the former.

Figure 3. Penghu 1 mandible.

(a) Mandible, (b) its virtual reconstruction and (c) surface rendered image of the segmented mandibular dentition (upper, lingual view) and its horizontal micro-CT section at the level indicated by the dotted line (lower).

Figure 4. Box plots of mandibular and dental arch metrics (mm) and ratio (%).

Symbols give the median (horizontal line inside the box), central 50% range (box margins), range (vertical line) within inner fences (1.5 times box range from box margins) and outliers (asterisk). Each cross represents an individual specimen. The Penghu 1 mandible is short and moderately wide (a–c). Because M₃ failed to develop in Penghu 1, its alveolar arcade index measured at distal M₂ was compared with both the index at distal M₂ (d) and that at the last molar (e) for the comparative specimens. Although it is uncertain which comparison is more appropriate over the other, in either case, the arcade of Penghu 1 is wider than H. habilis, Dmanisi and older Javanese H. erectus. The mandibular body of Penghu 1 is low (f,g), but its robusticity indices are moderately or extremely high at the symphysis (h) and lateral corpus (i), respectively. Penghu 1 is more similar to the African and some European Early-Middle Pleistocene Homo mandibles rather than to Javanese and Chinese H. erectus in these respects. On the other hand, Penghu 1 is closer to Asian H. erectus showing relatively thinner symphyseal width as compared with lateral corpus width (j). Ramus height of Penghu 1 is, when two different measurements are considered together (k,l), considerably lower compared with the Early-Middle Pleistocene African Homo and closer to Eurasian Homo specimens from the late Early to Late Pleistocene contexts. The antero-posterior width of the ramus (m) of Penghu 1 is also lesser compared with the African and Georgian mandibles, but is slightly larger than or comparable to the medians for the Middle-Late Pleistocene Eurasian samples. The medio-lateral condylar length (n) is extremely small and comparable to one of the Zhoukoudian mandibles (Mandible H1) and to the smallest range for H. sapiens. The incisal portion of Penghu 1 is extremely wide (o). Only one of the H. habilis (rudolfensis) specimens (KNM-ER 60000 (ref. 70) matches this Penghu 1 condition. The premolar portion is also extensive in Penghu 1 (p).

Figure 5. Bivariate plots of selected measurements.

Dimensions of mandibular corpora (a) and crowns of mandibular second molar (b) (in mm). Polygons indicate ranges when the sample size >3. The dental metrics of the MP European sample is divided into the smaller group (Atapuerca-SH) and the rest of it. Symbols: A, late EP European Homo (Atapuerca); B, Sangiran Upper (younger EP Javanese H. erectus); D, Dmanisi; d, Dingcun; H, Hexian; h, Huanglong Cave; P, Penghu; S, Sangiran lower (older EP Javanese H. erectus).

Figure 6. Results of the PCA based on four size-standardized mandibular metrics.

Scores for PC1 (a) and PC2 (b) against the ‘size variable’ (defined here as the geometric mean of the four measurements). Symphyseal height and width and corpus height and width at M₁ were used as the variables after divided by the size variable for each specimen. The principal component analysis (PCA) is based on the correlation matrix. Specimen names are indicated for archaic mandibles at least in one of the two figures. Those not indicated in either figure can be identified from the other figure because the two figures share the x-axis. The component loadings indicate that PC1, which explains 69% of the total variance, highly correlates with heights (positively) and thicknesses (negatively). PC2 explains 23% of the total variation, and tends to place those specimens with smaller symphyseal/lateral corpus thicknesses proportions on the positive side. The low PC1 score of Penghu 1 reflects its low and thick corpus. Irrespective of overall size of the corpus, Penghu 1 clusters with some of the Afro-European Homo from the Early-Middle Pleistocene contexts (for example., OH 13, 22; KNM-BK 8518; D211; Arago XIII), but remote from Asian H. erectus, Neanderthals and early H. sapiens. In contrast, in PC2, Penghu 1 scores high together with Asian H. erectus, and is markedly different from African and Georgian Early-Middle Pleistocene mandibles. The score for Penghu 1 is around the highest end of variations exhibited by European archaic mandibles.

Figure 7. Comparisons of the maxillary dental metrics (in mm).

(a) Bivariate plot for M². Polygons indicate ranges when the sample size >3. The dental metrics of the MP European sample is divided into the smaller group (Atapuerca-SH) and the rest of it. (b) MD diameters of I¹. Sample ranges are shown by the coloured longitudinal lines with each cross indicating individual specimen. The two older Javanese EP H. erectus specimens are Sangiran 7–85 and 7–86, whose reported stratigraphic levels are somewhat ambiguous. Symbols: A, late EP European Homo (Atapuerca); B, Sangiran Upper (younger EP Javanese H. erectus); C, Chaoxian; D (orange), Dmanisi; D (red), Denisova; d, Dingcun; G, Gongwangling (Lantian); H, Hexian; J, Jinniushan; p, Panxian Dadong; S, Sangiran Lower (older EP Javanese H. erectus); X, Yunxian (Meipu); x, Xujiayao; Y, Yuanmou.

Figure 8. Occurrence of thick mandibles and large M2s and I1s in Asia.

Thick lines indicate the presence of these features. Chinese ‘late archaics’ are represented by Jinniushan, Xujiayao, Chaoxian and so on. Possible age ranges are indicated for Penghu and Hexian with their likely ages by solid lines. The occurrence of different hyaenid taxa (Pachycrocuta at Hexian and Crocuta at Penghu) suggest that Hexian predates Penghu.