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2019 SAF Discovery Awards|Callao Cave and the discovery of the Homo luzonenesis

From:shanghai-archaeology-forum.org NetWriter:Date:2019-12-31

Archaeological investigations at Callao Cave, northern Luzon, Philippines resulted in the discovery of new species of hominin, Homo luzonensis. This is the most significant palaeonthropological discovery in Eurasia since the announcement of H. floresiensis in 2004. Direct dating of human fossils and the indirect assays on deer teeth using laser ablation U-series indicate a minimum age of greater than 50 – 67 kya. The skeletal elements exhibit a mosaic of archaic (primitive) or Australopithecine-like features and more derived or H. sapiens like attributes that suggest a unique evolutionary pathway for Homo luzonensis. Homo floresiensis on the island of Flores also demonstrates some distinctive morphological traits not dissimilar to those of H. luzonensis, including small size. Both islands have evidence of Middle Pleistocene hominin colonization providing a significant time-depth to facilitate evolutionary convergence and/or reversal under the influence of insular evolution.

At present the youngest proposed dates for H. luzonensis overlap with the earliest known presence of anatomically modern humans in China and Southeast Asia. In the Philippines, the oldest remains identified so far are from Tabon Cave, Palawan date to after 40 kya, but there is still a possibility that interaction occurred. At Liang Bua, recent re-assessment of archaeological stratigraphy has indicated a presence of H. sapiens shortly after the latest H. floresiensis fossils recorded. Genetic studies also hint at a possible presence of Denisovans in the Philippines (and Australasia) adding to the potential hominin diversity and potential interaction in the region.

In addition to H. luzonensis there have been some other significant archaeological discoveries and research in Island and Mainland Southeast Asia that have suggested an early modern human migration into Island Southeast Asia by 70,000 years ago, the first evidence of a hominin presence on Sulawesi and greater than expected hominin diversity in Indonesia.

The discovery of H. luzonensis resulted in considerable media coverage both in the Philippines and internationally, being reported in outlets such as the New York Times and Washington Post, with an altmetric score amongst 2830. To date, the excavations have produced 13 hominin fossils, comprising five hand and foot bones, seven teeth (including five post-canine teeth from the right maxilla of a single individual) and the broken femur shaft of a juvenile. All the hominin skeletal elements were recovered from the same stratigraphic deposit, Layer 14. The juvenile femur shaft and two right maxillary 3rd molars indicates the presence of at least three individuals. The skeletal elements exhibit a mosaic of archaic (primitive) or Australopithecine-like features and more derived or H. sapiens like attributes. However, a number of significant outstanding questions remain. Although, it is proposed that H. luzonensis was diminutive (and reported in some news outlets to be less than 4 ft tall), none of the skeletal remains recovered so far are useful for estimating an accurate stature. Morphological characteristics in the hands and feet suggest that H. luzonensis possessed tree-climbing (arboreal) abilities but do not provide enough detail to precisely reconstruct locomotive capabilities and dexterity (especially in the hands). In terms of evolutionary process, are the mosaic of archaic and derived morphological characteristics observed in H. luzonensis a result of island evolution in isolation on Luzon, or are some or all of the physical traits exhibited by this hominin symplesiomorphic – that is ancestral characteristics shared with much more ancient ancestors such as Australopithecus? Answers to these questions would provide invaluable new insights not only into the evolutionary history of H. luzonensis but how isolation on islands influences the evolutionary trajectories of hominins more generally. It will also provide us with a greater understanding of the ancestral relationships between hominin species and even our interpretations of the timing of hominin migrations out of Africa and across Eurasia.

In 2010 Mijares and others reported the recovery of several fragments of mammal bone with cutmarks in close association with the hominin remains. However, as yet no artefacts have been recovered from Layer 14. However, previous excavations at Callao have enabled interpretation of the depositional history of the Layer 14 sediments that illustrate the post-depositional impacts on the spatial distribution of bones. Layer 14 is a bone breccia or cemented calcium carbonates layer. The reconstructions suggest that precipitation run-off (rainwater) has resulted in the movement of bone fragments from close to where the southern entrance now exists towards the cave interior. Small pieces of ‘light’ bone and loose teeth have potentially moved further than heavier materials such as stone artefacts, which remained closer to the current cave entrance.

More archaeological excavation at Callao Cave and nearby caves are planned in the next few years.  The team is hoping to recover more diagnostic fossil remains that may answer question of stature and facial attributes as well as address some of the dating problems.

Biographic Sketch

Armand Salvador B. Mijares is an Associate Professor 7 and a UP Scientist 1 at the Archaeological Studies Program, University of the Philippines. He was a former Director ASP from 2012 to 2016 and Deputy Director from 2007-2011. Prior to joining the academe, Dr Mijares worked as a Museum Researcher and Head of the Terrestrial Archaeology Section of the National Museum of the Philippines.

He received his PhD in Archaeology and Palaeoanthropology from the Australian National University 2006. He also has an MS in Anthropology major in Archaeology from the University of New Mexico as a Fulbright scholar and an MA in Anthropology from the University of the Philippines.

His research interest is on Pleistocene Archaeology, lithic usewear analysis, geoarchaeology and cave archaeology. He has published numerous articles in scientific journals and book chapters in academic press.  As an anthropologist he has conducted ethnographic research among the Mangyans of Mindoro Island.

Dr Mijares is the Project Head of the Going Deep in Time: The Archaeology of Callao Cave. It is in this project, in collaboration with an international team, that he discovered the new hominid specie: the Homo luzonensis.