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The Giant Rats of Timor

The Giant Rats of Timor

By Julien Louys

Giant rats coexisted with humans for 40,000 years on the island of Timor. Their extinction is a cautionary tale about the ecological consequences of deforestation in South-East Asia today.

Arriving on the island of Timor more than 40,000 years ago, the first inhabitants would have been confronted with an astounding sight: rats the size of cats and small dogs scurrying through the trees and undergrowth of the forests. Rather than being frightened, however, these early inhabitants must have been delighted at the delicious bounty on offer. Archaeological excavations throughout Timor-Leste, which preserve the records of what people ate and how they lived for forty millennia, has unearthed thousands of chewed, cut and burnt bones of giant rats. It’s clear people were hunting and trapping these rats for food, cooking them over open fires, and discarding their chewed remains on the cave floors.

The island of Timor is situated at the eastern end of a region known as Wallacea, which consists of more than 17,000 islands that have never been connected to either the South-East Asian or Australian continents (Fig. 1). Many of the plants, fungi and animals that call these islands home must have travelled across the seas at some point to get there.

Sea crossings are not easy for terrestrial organisms, which require access to nutrients and fresh water in order to survive. Any species newly arriving on an island are faced with novel ecosystems, as each island is a unique blend of the species that were able to get there. And, once on the island, reproductive choices can be quite limited: most islands have limited resources that can only support small populations of species that are usually descended from an even smaller number of colonising individuals.

Because of this, weird things can happen to organisms that manage to reach and colonise isolated oceanic islands, particularly mammals. Large species like elephants and hippopotamuses shrink down in size, some to no more than 200 kg, or about 2% the size of their ancestors. On the flipside, traditionally small mammals like rats can reach gigantic proportions. This ecological phenomenon is commonly termed the “island rule”, and Timor is no exception to this.

Long before people arrived, Timor hosted small elephant-like creatures known as stegodons. Arriving perhaps at around the same time at the stegodons were four or five different species of rats, some of which would eventually became much larger than their ancestors (Fig. 2). The largest of these, in fact the largest rat in the world, weighed in at 5 kg, or ten times the size of the modern black rat. Not all of Timor’s rats were that large, although the smallest of the giant rats was a still an impressive 1.5 kg. By the time humans arrived on Timor there were at least seven different species of giant rats that lived alongside several native species of regular-sized rats, lizards and snakes.

It’s still not known exactly when the ancestors of the giant rats first got to Timor, and how long they lived in splendid isolation before people arrived. This is because until recently all of the giant rat fossils have been recovered from archaeological deposits (Fig. 3). However, a natural fossil accumulation of giant rats was recently discovered, and it is hoped that this site will provide insights into the ancient history of these rodents.

Moreover, because the giant rat fossils represent the scraps and discards from many cave dinners, and the specimens recovered are usually broken up and burnt, it’s difficult to work out exactly where these different species lived and what they ate. We do know, by examining how their teeth and jaws look, and in comparison with modern species with known diets, that these animals were mostly eating grains, grasses and other vegetable matter (Fig. 4).

While we still don’t know much about the biology and ecology of these giant rats, the environments they preferred or how so many different species were able to live together, one thing we do know is when they finally became extinct.

Fort Building and Extinctions

The remains of fortified structures are abundant in many parts of Timor-Leste. These structures are often found on hilltops and cliff edges, and consist of massive stone walls up to 4 metres in height and 2 metres depth coming out of the jungle overgrowth (Fig. 5). It is thought that the large scale and prolific construction of these defensive structures began as early as AD1300 and was driven by escalating conflicts between Timorese villages, in turn driven by the demand for scarce resources, in particular the increasingly rare sandlewood.

Timor was famous in the medieval Asian world for the export of white sandlewood – a fragrant timber used in the manufacture of perfumes and incense used in the religious ceremonies of many different faiths. As early as AD1225 Timor is mentioned in the written trade records of China as an important source of sandlewood, which was traded to Chinese junks for silver, cloth, ceramics and iron.

The latter had huge ramifications for Timor. The introduction of iron allowed more large-scale harvesting of sandlewood than had previously been possible with more primitive implements. Iron tools would also have allowed massive forest clearance for agriculture. Today only 15% of Timor’s primary forests remains, all of it in isolated and mountainous regions. Exactly when iron was first introduced to Timor is not known, but it was certainly a valuable commodity by the time the Chinese trade records were written.

Commerce with foreign traders led to conflict between Timorese villages over access to limited resources. This necessitated the building of heavily fortified enclosures. By the time this building program had begun, the giant rats were extinct.

Not a single giant rat specimen has been found in any of the archaeological excavations of these forts to date. Other, smaller rat species have been recovered, as have more recently introduced larger animals such as dogs, deer and cattle.

Given how abundant the giant rats were in earlier archaeological excavations, it’s incredibly unlikely to think that their fossils were missed. It’s much more probable that the massive forest clearances that followed the introduction of iron into Timor destroyed most of their native habitats, and ultimately drove these incredible creatures to extinction.

Lessons from the Past

The fact that people caused the extinction of species on an island is hardly news. Island extinctions by people is a classic extinction scenario: humans arrive on an island that has never before known their presence and, within a very short period of time – sometimes only a few decades – the naivety of the endemic species combined with people’s voracious appetites wipes out all manner of delicious creatures. The dodo is perhaps the most famous example of this scenario.

Humans undoubtedly had a hand in the extinction of Timor’s giant rats, but what makes Timor really unusual is that the mechanisms of extinction didn’t come into play until tens of thousands of years after people arrived on the island. Other island giant rats did not fare so well. The giant rats of Tenerife, situated in the Canary Islands to the north-west of Africa, became extinct almost immediately after humans first arrived on the islands, so what makes the Timor rats so special?

It turns out that Timor’s giant rats aren’t unique in surviving so many thousands of years with people. Unbeknown to many, rats as large as some of Timor’s giants can still be found living on a few South-East Asian islands. New Guinea has by far the most, with at least four species of giant rats known to science, and probably several more species waiting to be described. Known as woolly rats due to their fuzzy pelts, these species can still be found living in the highlands of New Guinea today.

The nearby island of Flores still has one species of giant rat (Fig. 6) in addition to several species of extinct giants. The Philippines also hosts a couple of quite large rat species. Very little is known about any of these creatures, including exactly how many there are, what they eat, where they are found and what sorts of habitats they prefer. Most importantly, we don’t know how threatened they are, or what these threats might be.

Although now long gone, we can learn some important lessons from the rats of Timor that might help preserve the giant rats still with us. The fossil record of Timor shows that despite more than 40,000 years of hunting and eating, people did not overhunt the giant rats to extinction. This suggests that sustainable hunting by traditional peoples on New Guinea, Flores and the Philippines are unlikely to threaten similar species.

However, massive deforestation on Timor 1000 years ago, and occurring right now throughout South-East Asia, is likely to reduce suitable habitats to a point where populations just won’t be sustainable.

Rats evoke feelings of disgust and fright in many people, but not all rats are created equal. Many species are shy forest-dwellers under the risk of extinction. Preserving primary forests is critical to ensuring that these shy giants aren’t gone before we can get to know them a little better.

Julien Louys is a postdoctoral research fellow at the Australian National University’s College of Asia and the Pacific.