Hundreds of thousands of years ago, the Madura Strait – a 9,500 km² area of water that stretches between the Indonesian islands of Java and Madura – looked very different to how it does now.

Back then, it was part of a vast lowland area called Sundaland in which animals like crocodiles, elephants, and rhinos thrived.

Nowadays, what was once grassland and river is a relatively shallow sea; what were once hilly and mountainous areas now form the Indonesian archipelago upon which people (and wonderful biodiversity) still reside.

But echoes of the life and times of Sundaland still remain – as evidenced by fossils discovered by researchers during recent dredging of the Madura Strait.

Until now, no fossils had been recovered from this area of seabed, leading researchers to speculate exactly who or what had thrived in this specific area of lowland in prehistoric times.

However the fossils tell a new story: across 36 vertebrate fossils, researchers have learned a lot about life in Sundaland, in particular the staggering revelation from two of the skulls recovered, that Homo erectus once resided in this area.

Previously, Homo erectus had only been known to have lived on Java. However, the team’s findings detail not only the location of our predecessors, but their dietary and hunting habits too, as Leiden University archaeologist Harold Berghuis explained in a statement:

“Here they had water, shellfish, fish, edible plants, seeds and fruit all year round. We already knew that Homo erectus collected river shells. Among our new finds are cut marks on the bones of water turtles and large numbers of broken bovid bones, which point to hunting and consumption of bone marrow.”

But the Homo erectus were simply two of many notable fossils the team found in their operations.

In fact, as the team’s paper – which was recently published in the journal Quaternary Environments and Humans – explains, their findings support the idea of a truly luscious Sundaland in which a huge range of flora and fauna thrived.

Though Indonesia is still incredibly biodiverse today, Sundaland’s biodiversity was incomparable, as Berghuis continued:

“Most of these species are extinct, whereas others are the ancestors of species that still occur in the region, but whose survival is seriously threatened. The Asian hippo is extinct. Carnivorous Komodo dragons are now restricted to the islands of Komodo and Flores, and river sharks are extremely rare in the major rivers of India and Thailand. But all these animals were thriving in ancient Sundaland. This knowledge is hugely important to our understanding of the biodiversity of the whole of Southeast Asia.”

Though it is impossible to reinstate or recreate the wilderness of Sundaland, an understanding of the plants and animals that once called this area home is both fascinating and important to our conservation efforts. By understanding what came before, we can grapple with how to protect those who live there now.

Meanwhile the fossils reside in Badung, Indonesia’s Geological Museum, where they belong. Here they can inform generations about what truly lived in Indonesia long, long ago.

If you thought that was interesting, you might like to read about the mysterious “pyramids” discovered in Antarctica. What are they?