Hundreds of stone tools and animal bones, including the best part of a rhino skeleton showing signs of butchering, were unearthed on the island of Luzon.

Published in the journal Nature on Friday, they push the date of human occupation in the archipelago back hundreds of thousands of years.

Precisely who these rhino-eating colonisers were remains a mystery, said study co-author Gert van den Bergh, a palaeontologist at the University of Wollongong, but there’s little chance they were of our species, Homo sapiens.

“This remains speculative because we don’t have fossils yet, but the dates pre-date modern humans,” he said.

Even without fossils of the toolmakers themselves, the work fits in with evidence of early humans on nearby South-East Asian islands of Flores — home of Homo floresiensis or the Hobbit — and Sulawesi, according to Gilbert Price, a palaeontologist at the University of Queensland who was not involved with the study.

“The original story for human evolution was very basic, that maybe there was one single migration into places like South-East Asia, but it’s becoming so much more complicated now,” Dr Price said.

Food scraps and utensils

The new fossil haul isn’t the first to be found on Luzon: a US team found animal bones and stone tools back in the 1950s.

From these, palaeontologists suspected humans colonised the Philippines back in the Middle Pleistocene, between around 780,000 and 120,000 years ago.

But without accurate dating, they couldn’t be sure.

So the firmest earliest date for the human occupation in the Philippines was pegged at around 67,000 years ago, thanks to a foot bone belonging to a Homo species found in a cave in Luzon’s north.

In 2013, a team of palaeontologists including Dr van den Bergh, knowing that fossils had been found in the area before, started excavating in a valley in the neighbouring Kalinga province.

“For the first couple of weeks, we didn’t see much,” Dr van den Bergh said.

Three-quarters, in fact — the most intact skeleton found of the now-extinct Rhinoceros philippinensis.

Intriguingly, 13 of its bones showed clear cut marks. Two leg bones looked like they had been smashed — one was completely shattered — presumably to get at the marrow inside.

The team also found other animal remains alongside stone tools, including an extinct elephant called the stegodon, deer and monitor lizards.

To find out how old their finds were, the researchers enlisted the help of labs to deduce the age of the sediment surrounding the artefacts, as well as directly dating a rhino tooth.

Volcanic minerals gave a maximum age of 1 million years. The tooth and sediment grains turned up dates of around 700,000 years, plus or minus 70,000.

Taken together, the researchers wrote, “it follows that the rhinoceros skeleton was buried by a mudflow” at least 631,000 years ago.

Who butchered the rhino and how did they get there?

Given Homo sapiens has only been around for a few hundred thousand years, the most likely Luzon-dweller is Homo erectus, according to Dr van den Bergh.

Unfortunately, without fossilised bones belonging to the mystery rhino-eaters, there’s no way to identify them.

Their tools were a standard run-of-the-mill style, produced by many Homo species around the world.

Ancient DNA isn’t a viable route either. The heat and humidity of the tropics degrade it quickly, Dr van den Bergh said.

So the team is continuing to excavate and hopefully find remains of those elusive toolmakers.

The work not only shows that humans were around a lot earlier than thought, and probably migrated in waves rather than in one big hit, but it also has interesting implications about how they got there, Dr Price said.

During past millennia, various ice ages dropped sea levels, so it may have been possible to walk to some islands of the Philippines — but not Luzon, which is surrounded by deep water.

One method of “accidental dispersal” is being picked up and washed across by a tsunami.

“You can’t say these early people took purposeful sea voyages on boats or anything like that — there’s no evidence for that at all,” Dr Price said.

“But you think about the other animals that were around at the time, like the rhinoceros, freshwater turtles and deer, they probably were washed across too.

“So these accidental dispersals that sent over rhinoceros may have sent humans across at the same time.”

-ABC