Washington, Dec 19 (PTI) The last known settlement of Homo erectus, one of modern humans' direct ancestors who disappeared around 4,00,000 years ago, was situated in Ngandong, on the Indonesian island of Java, a new study says.
According to the researchers, including those from the University of Iowa in the US, the human ancestors existed on the Indonesian island between 1,08,000 and 1,17,000 years ago.
The study, published in the journal Nature on Wednesday, time-stamped the site by dating animal fossils from the same bonebed where 12 Homo erectus skull caps and two shinbones had been found.
The archeologists then dated the surrounding land forms -- mostly terraces below and above Ngandong -- to accurately record the pre-humans' possible last stand on the Earth.
'This site is the last known appearance of Homo erectus found anywhere in the world,' said study co-author Russell Ciochon, professor in the Department of Anthropology at the University of Iowa.
'We can't say we dated the extinction, but we dated the last occurrence of it. We have no evidence Homo erectus lived later than that anywhere else,' he added.
The new age estimates were made after assessing samples such as animal fossil fragments and sediment from the rediscovered fossil bed where the original Homo erectus remains were found by Dutch surveyors in the 1930s.
In addition, the researchers also estimated when mountains south of Ngandong first rose by dating minerals from caves in the Southern Mountains.
Using these information, they determined when the Solo River began coursing through the Ngandong site, and the river terrace sequence was created.
'You have this incredible array of dates that are all consistent. This has to be the right range. That's why it's such a nice, tight paper. The dating is very consistent,' Ciochon said.
He said the fossils could be assessed thanks to changing landscape in the region.
'Fossils are the byproducts of complex landscape processes. We were able to nail the age of the site because we constrained the fossils within the river deposit, the river terrace, the sequence of terraces, and the volcanically active landscape,' Ciochon said.
According to the researchers, Homo erectus hopscotched its way across the Indonesian archipelago, and arrived on the island of Java about 1.6 million years ago.
At that time, they said, the area around Ngandong was mostly grassland, with abundant plants and animals -- the same environment that cradled the species in Africa.
While the pre-humans continued to venture to other islands, Java, likely remained home -- or least a way station -- to some bands of the species, the archeologists noted.
But around 130,000 years ago, the environment at Ngandong changed, shifting Homo erectus' fortunes.
'There was a change in climate. We know the fauna changed from open country, grassland, to a tropical rainforest (extending southward from today's Malaysia). Those were not the plants and animals that Homo erectus was used to, and the species just could not adapt,' Ciochon explained. PTI VIS VIS VIS