Kathryn Manalo takes a closer look at the 709,000-year-old remains of a Rhinoceros philippinensis unearthed from the town of Rizal in Kalinga. Jonathan Cellona, ABS-CBN News

MANILA - It was just "an ordinary day" in 2014, recalled researcher Kathryn Manalo, when their group found a "rock" in Rizal, Kalinga that led to what could be one of the most important archaeological discoveries so far in Philippine history.

"We found a rock-like thing. The local people who were with us said that's just a rock. But I thought the shape was so strange," shared Manalo, a former senior lecturer and researcher of the University of the Philippines Archaeological Program.

The "rock-like thing" turned out to be a 709,000-year-old tooth, which they later discovered was a part of an extinct rhinoceros butchered by early humans living in the Philippines, pushing the first known human activity in the country 10 times earlier.

A tooth from an extinct rhinoceros species excavated from an archaeological site in Kalinga. This is just one of the remains of a butchered rhino discovered in 2014. Jonathan Cellona, ABS-CBN News

"We were not expecting something because that's what archaeologists actually do," recalled Manalo, whose group eventually found 75% of the skeleton. "At that time, we haven't realized the impact of what we found."

The team, led by professor Thomas Ingicco of the Muséum National d'Histoire Naturelle, and Clyde Jago-on and Marian Reyes of the Philippine National Museum, found out that 13 of the rhino's bones have cut and percussion marks left by human-made stone tools.

The butchery marks suggest that these mysterious early humans settlers in the Southeast Asian island smashed the bones with their hand-made tools to access the tasty marrow part. Cut marks also suggest that they have tools to deflesh rhino meat.

A dent left by impact of a human-made stone tool on a fossilized bone of a rhinoceros that was excavated in Rizal, Kalinga. Jonathan Cellona, ABS-CBN News

The team also found lithic or stone tools and other pre-historic animal remains on the same Kalinga excavation site, which tests show were also from the same time period as the rhinoceros' bones.

"Isang malaking push ito na magpapalakas ng identity natin as Filipinos, na parang sa Pilipinas pala, 700,000 years ago, may sinaunang tao na, hindi lang 67,000 years ago," Manalo said, referring to the "Callao Man" discovered in Cagayan in 2007.

(This strengthens our identity as Filipinos, by just having the knowledge that humans lived here 700,000 years ago, not just 67,000 years ago.)

The 17-page study of the archaeological teams said it is even possible that the "diminutive Callao hominin may represent a direct descendent from a Pleistocene migration stock related to these early Kalinga toolmakers."

Searching for the 'Kalinga toolmaker'

Lithic artifacts from Kalinga. Nature (02 May 2018)

The bigger question, however, is where to find the remains of the hominins—the scientific term for early humans—who crafted the tools for either hunting or scavenging rhinoceros in the Philippines during 700,000 years ago.

Manalo said rhinoceros are not unique to the Philippines during that time period. She said ancient rhinos in Southeast Asian countries like Indonesia are often associated to the human ancestor, Homo erectus.

"We don't have Homo erectus here in the Philippines. It's wrong to assume but the animals that were associated in that time period in Southeast Asia were related to Homo erectus. So we're hoping maybe to see or confirm that in the next season," she said.

A small arrow points to a cut mark left by a human-made stone tool on a rhinoceros bone. Jonathan Cellona, ABS-CBN News

Indonesia's "Java Man" and China's "Peking Man" are among the Homo erectus discovered in Asia. The Philippines' "Callao Man" may

either belong to Homo sapiens or Homo floresiensis. Palawan's "Tabon Man," meanwhile, has been classified as a Homo sapien.

Catherine King, a senior researcher of the National Museum who was also with the excavating team, said searching for human remains would be a little harder. She said it is even uncertain if the human remains will be found at all in Kalinga.

"'Yun talaga 'yung pinnacle: if we find a Homo erectus. Tama 'yung sinabi nung colleague ko, people—early humans—are very mobile. Ito kasi (rhinos), may ecosystem silang ginagalawan, so they just move around there. 'Yung mga tao, they go where the food is, gumagalaw sila," King explained.

(The pinnacle of this search is the finding of Homo erectus. My colleague was right in saying early humans are very mobile, unlike rhinos that move in an ecosystem. Early humans go where the the food is.)

The search for what could possibly be the remains of Homo erectus

in the Philippines, continues this June, said Filipino archaeologist Mylene Lising who was also with the team that discovered the 709,000-year-old rhino remains.

"Di natin alam kung mangyayari this season. Puwedeng wala kasi may season na isang bato lang ang nahahanap namin. May season na jackpot, buong rhino. Sana maka-jackpot kami ng bungo," said Lising, explaining that a season for them is only one month.

(We don't know what will happen this season. It's possible that we don't find anything at all. There were seasons when we only find one rock. There was this season we found almost a whole rhino. We're hoping to hit the jackpot, a skull perhaps.)