Tuesday, 27 January 2015

Archaic human recovered from seabed off western coast of Taiwan

Could partial lower jawbone be from a Denisovan – or an entirely new species?

A partial fossil human jawbone from Taiwan is reportedly the first archaic hominin to be found there. The jawbone was dredged by a fishing net from the 60 to 120 m (200 to 400 ft.) deep Penghu Channel, 25 km (15.5 miles) of the island’s western coast. Also recovered were vertebrate fossils known as the terminal Middle/Late Pleistocene ‘Penghu fauna’. Both Taiwan and the Penghu Channel were part of the Asian mainland during Pleistocene episodes of lowered sea levels. The jawbone found its way to an antique shop in Tainan City, where it was purchased by a local man who in turn donated it to the National Museum of Natural Science of Taiwan.

The nature of its recovery means that there is no stratigraphic data by which the Penghu 1 jawbone can be dated. Accordingly, researchers measured its fluorine and sodium content in relation to that of other Penghu fossils. Fluorine, deriving from the surroundings, tends to accumulate slowly over time in buried bones; sodium on the other hand exists at about one percent in the bones of living vertebrates, but decreases when they are fossilised. By this means, the researchers matched Penghu 1 with fossil remains of Crocuta crocuta ultima, an extinct Eurasian subspecies of the spotted hyena that reached northern China between 500,000 and 250,000 years ago, but did not reach southern China until 240,000 years ago. There were episodes of lowered sea levels between 190,000 to 130,000 years ago and from 70,000 to 10,000 years ago; Penghu 1 probably dates to one of these two intervals.

Penghu 1 is identified as archaic by its relatively large molars and premolars, and by its lack of a chin. The short and relatively wide shape of its dental arcade is derived in comparison to the earliest humans (Homo habilis and the Dmanisi hominins), but other than that it cannot readily be assigned to any particular archaic human species. The second molar is larger than those of other archaic Asian hominins, and the low, thick body is closer to some examples African and European Homo from 400,000 years ago than to Early/Middle Pleistocene Asian Homo, with the exception of the 400,000-year-old Chinese Hexian Homo erectus remains.

The large second molar suggests Denisovan affinities in M2 crown size, but unfortunately no Denisovan lower jawbones or lower M2 teeth have yet been found for comparison. Not until we have a Denisovan lower jawbone that can be identified as such by genetic means will we have a better idea if Penghu 1 belonged to a Denisovan.  Nor can we rule out the possibility that Penghu 1 represents a completely new archaic human species.

Chang, C. et al., The first archaic Homo from Taiwan. Nature Communications 6, 6037 (2015).

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