In January this year, a team of international researchers caught the attention of the global scientific community with its findings that a partial jawbone fossil discovered off the western coast of Taiwan could indicate the existence of a hitherto unknown archaic species of human. Published in an article in the journal Nature Communications, the research results note that the mandible is significantly larger than those of virtually all other ancient hominins known to be living in the region around the same time. “We have a new story to tell about human evolution, a story from the time when Taiwan was connected to continental Asia,” says Chang Chun-hsiang (張鈞翔), the lead author of the article and chair of the Department of Geology at the National Museum of Natural Science (NMNS) in central Taiwan’s Taichung City.
The ancient jawbone was dredged up by fishermen working in the Penghu Channel about 25 kilometers off the coast of Tainan City in southwestern Taiwan. The mandible was sold to an antique collector in 2008, who then handed it over to the NMNS in 2010. The find consists of a remarkably complete right lower jaw with four intact though extensively worn molars and premolars as well as cavities for four incisors and a canine.
Researchers were immediately able to determine that the jawbone did not belong to a member of Homo sapiens, the only extant human species, due to the absence of one key feature—a chin. “Modern humans all have a protuberance of some size on the front of the lower jaw,” explains Chang, who began working for the NMNS in 1993 as a fossil researcher. “In contrast, the Penghu 1 mandible has a flat anterior surface that recedes downward.”
This characteristic is similar to the jawbones of major Homo erectus discoveries, such as Java Man and Peking Man, which were found in Indonesia and mainland China, respectively, and are estimated to be more than 700,000 years old. Significantly, however, the Penghu 1 jawbone is notably larger than those of Java Man and Peking Man, which indicates that it belongs to either a previously unknown subgroup of Homo erectus or an entirely separate hominin species.
Penghu 1 constitutes the first proof that archaic relatives of modern humans lived in Taiwan. In the past, the oldest evidence of a human presence came from fossils found in the early 1970s in today’s Zuozhen District of Tainan City. Those remains, which include three cranial fragments and a molar tooth, belonged to an anatomically modern human and are estimated to be around 20,000 years old. The Penghu 1 mandible is likely much older than this, though accurately dating the discovery has proven problematic.
Chang explains that it is far more difficult to ascertain the age of underwater findings, particularly when a fossil was caught in a fishing net rather than carefully unearthed by paleontologists. “As Penghu 1’s stratigraphic context is unknown, its age can only be determined by analyzing the jawbone itself,” he explains. “Typically, we use uranium-series dating to establish the age of fossils, but it had limited success in this case as radioactive materials in the bone sample had dwindled significantly due to its long immersion in seawater.”
The right lower jawbone, teeth and virtual reconstructions of the complete lower jaw and teeth of Penghu 1. (Photo courtesy of Chang Chun-hsiang)
Therefore, the researchers decided to also employ fluorine dating, which can help establish how long something has been buried, and ultimately determined Penghu 1 to be approximately 190,000 years old. However, the margin for error for the dating procedures means the jawbone could be as old as 450,000 years or as young as 10,000 years.
Over the decades, numerous animal fossils have been found in the 60 to 120-meter-deep undersea trench where the Penghu 1 mandible was discovered. These include remains of archaic species of bear, deer, dog, elephant, horse and pig from the Pleistocene Epoch, which lasted from around 2.6 million to 11,700 years ago. “This epoch saw repeated glaciations, which caused sea levels to fall and created a land bridge between Taiwan and the Asian continent,” explains Chang, who was awarded a doctoral degree in paleontology from University College London in the United Kingdom for his research into the evolution of elephants. “During these periods, many animals moved to warmer southern regions such as Taiwan.”
Many fossil sites were subsequently submerged when sea levels rose. However, the Penghu Channel’s strong underwater currents, which are caused by large disparities in seabed levels, regularly wash out buried fossils. “We’ve previously found animal bones with human-made cut marks in them,” Chang says. “We’ve also discovered pieces of bone that we suspect are from ancient hominins, but the fossils are too small and fragmented to be identified.”
The international effort to study the Penghu 1 mandible evolved out of prior collaborative projects to analyze mammal fossils found in Taiwan. Before teaming up to study the jawbone, Chang and Masanaru Takai from the Primate Research Institute at Kyoto University in Japan had conducted research on fossils of monkeys found in early to middle Pleistocene sediments in Zuozhen. “Just a handful of academic institutions in Taiwan conduct archaeological and paleontological studies, so we often require help from abroad,” Chang notes.
Once the two researchers realized the potential significance of the Penghu 1 jawbone, they sought the assistance of a number of other prominent scientists in the region, including Yousuke Kaifu, a senior researcher in the National Museum of Nature and Science’s Department of Anthropology in Tsukuba City, Japan. Kaifu then asked scientists from the Research School of Earth Sciences at the Australian National University in Canberra to conduct the uranium-series dating on Penghu 1. Another Japanese researcher, Shuji Matsuura from the Laboratory of Physical Anthropology at Ochanomizu University in Tokyo, performed the fluorine dating.
The discovery of Penghu 1 marks an important step in efforts by regional researchers to improve their understanding of the archaic creatures that lived in East Asia during the Pleistocene Epoch. When Chang first began conducting paleontological research in the 1990s, he focused on studying Pleistocene elephantid remains recovered from the Penghu Channel. Over time, he and other prominent researchers have gradually developed a more complete understanding of the mammal groups that were prevalent during low sea-level episodes when the Taiwan Strait was a land mass.
A number of scientists and technicians from across the region participated in studying the hominin fossil. (Photo courtesy of Chang Chun-hsiang)
To date, the fossilized mandible is without question the most significant discovery that has emerged from the channel, particularly as it is notably different from almost all other hominin finds in the region. Chang points out that while smaller jawbones and teeth are a sign of evolutionary advancement, Penghu 1 possesses a larger mandible and teeth than the much older Java Man and Peking Man.
The only remains from roughly the same period that share the same basic morphological features as Penghu 1 are from robust-jawed hominins uncovered in Hexian in the eastern mainland Chinese province of Anhui. While it is tempting to designate the Hexian finds and Penghu 1 as new subspecies of Homo erectus, their evolutionary links with this form of archaic human need to be examined further before they can be assigned to any particular grouping, Chang notes.
If Penghu 1 is a rare subspecies of Homo erectus, “this discovery extends the geological distribution of Homo erectus in Asia to its eastern periphery,” the NMNS researcher says. And regardless of whether it comes from an entirely new species or a rare variant of Homo erectus, the jawbone highlights the diversity of archaic human populations on the continent. Furthermore, the fossil indicates that primitive features such as large mandibles and teeth were still in existence less than 190,000 years ago. Indeed, it is even possible that Penghu 1 hominins came into contact with Homo sapiens when modern humans began migrating to the Asian continent in the last 50,000 to 40,000 years.
While at present researchers are unable to state with certainty how such a primitive hominin species managed to remain in existence for so long, Chang has a theory that could explain this. “Unlike other animals such as mammoths that moved to Siberia and in that freezing place developed long hair and curved tusks, there might have been a migration of robust-jawed hominins from other parts of the continent to modern-day Taiwan, where they retained much of their original form,” he says. “The region, with its varied climate and topography, would certainly have provided quite agreeable living conditions for these creatures.”
That is to say, these primitive hominins found “a place which to them must have been like utopia” and therefore they did not have to evolve much, Chang notes. Once lost to history, these early inhabitants of Taiwan are now challenging established theories about human evolution. Furthermore, the Penghu 1 jawbone provides compelling evidence that multiple lineages of archaic hominin species coexisted in Asia before the arrival of Homo sapiens.
Write to Pat Gao at cjkao@mofa.gov.tw