The paper in Nature is here: https://go.nature.com/2roykIS
Like a great adventure tale, it started with a found manuscript. Back in 2013, while sorting through papers and books donated by Dr. Wilhelm Solheim, a noted American archaeologist, to the library of the Archaeological Studies Program of the University of the Philippines (UP-ASP), we came across the journal of Laurence L. Wilson, a petroleum prospector and amateur paleontologist who worked in the northern Philippines in the 1950s. The journal contained clippings of newspaper and magazine articles about Southeast Asian paleontology, correspondences with geologists and anthropologists from the University of the Philippines and accounts of fossil hunting expeditions that he undertook. Included in the journal is a letter that H. Otley Beyer, then head of the Department of Anthropology of the University of the Philippines, wrote to Wilson requesting him to guide the German paleontologist G.H. Ralph von Koenigswald on a field survey to Northern Philippines. Von Koenigswald by this time is known for his study on the paleontology of Java, Indonesia and notably for the discovery of Mojokerto 1, a complete skull cap from a juvenile Homo erectus now dated to around 1.49 ± 0.13 Ma.
In one entry, Wilson detailed an expedition that he made to the mountains of Kalinga in Northern Philippines. This particular entry caught our attention because he mentioned that he found teeth and bones of Rhinoceros, an animal usually associated with the Middle Pleistocene of the Philippines. The entry also included photographs of the area and a hand drawn map of the localities he visited. The localities are not far from the Cagayan Valley, an area which has been surveyed and excavated since the 1930s and is known for its rich Pleistocene fauna. We decided that it will be worthwhile to look at the sites mentioned by Wilson, just to see how it relates geologically to the Cagayan Valley sites and whether there is any preserved stratigraphy that can be associated with the fossils. During this time, we were looking for evidence of early human occupation in the Philippines, a two-man team doing foot survey in areas not far from the University of the Philippines. We were specifically interested in addressing two questions. First, we were interested in biochronology and the Pleistocene faunal turnover in the Philippines. Although some fossil mammal species have been described for the Philippines in terms of taxonomy, very little is known about the distribution of these animals through time. So we were on a search for fossil bearing deposits that can be stratigraphically correlated. Second, previous surveys and excavations in the Cagayan Valley yielded stone tools in addition to fossil fauna. But the stone tools were never found in any secure deposits or in sedimentary beds associated with fauna. Again, we were thinking that a site with a continuous stratigraphic sequence would help address this issue.
We set up a small survey team, made up of researchers from the National Museum of the Philippines who led an excavation in the area in the 1970s and the UP-ASP, and visited the sites along the Cabalwan ridge mentioned in the journal entry. The survey team was also joined by Dr. John de Vos, then curator of the Dubois collection at the Naturalis Biodiversity Center in the Netherlands. J. de Vos, an expert in the Pleistocene fauna of Southeast Asia, has excavated in the area with tentative results in 2001. We identified specific locations of interest in the area for a formal archaeological excavation. We also found the trenches from the 2001 and 1970s excavations. In the course of this survey, we also discovered tusks of Celebochoerus, an extinct pig first thought to be restricted to the island of Sulawesi in Indonesia South of the Philippines. This fossil, which we described and named, is important since it hints on the possible Philippine origin of at least some of the well-described Sulawesi fauna.
Formal excavations started in 2014, by an international team of researchers from the French National History Museum, the National Museum of the Philippines, the University of Wollongong, the University of Tarragona, the Max Planck Institute for the Science of Human History, the University of Paris-Saclay, the French Institute of Research for Development, the University of Athens, and the local government of Rizal, Kalinga, the town where the site is located. A week into the excavation, we found in a corner of the first trench we opened, a meter below the surface, a fossilized rhinoceros tooth. This tooth was sampled for electron spin resonance and Uranium-series dating and returned a date of 709,000 years. Intuiting that there could be an accumulation of materials in the corner where the tooth was found, we extended the excavation by opening a test pit north of the trench. We were proven right when a few days later, we found a rhinoceros ulna and right next to it, the first stone artifact of the season, a quartz core. We also found fossilized remains of other animals, including carapace fragments of a fresh water turtle. When more rhinoceros bone fragments started to turn up a week into the excavation of the extension pit, we realized that we were excavating a complete rhinoceros skeleton. We changed the excavation strategy, opting for bamboo sticks instead of metal trowels to avoid damaging the fossils. While still embedded in the clayey sediment matrix, we observed clear butchery marks in one of the ribs we were excavating. This in addition to the stone artifacts that were turning up associated with the rhino skeleton got us convinced that we were dealing with evidence of hominin activity. We carefully retrieved the rhinoceros skeleton, sampled the site for datable materials and performed further analyses, the results of which are detailed in a paper recently published by Nature.
Since then we have been coming back to the site every year for a month-long excavation and we continue to recover fossils and artifacts, evidence of the very first hominin occupation of the Philippines, an archipelago that has never been connected to mainland Southeast Asia.
Marian C. Reyes, Noel Amano & Thomas Ingicco