What rats can tell us about the rise and fall of Homo floresiensis
by Tracey Skehan
For almost a million years, ‘hobbits’ lived on the Indonesian island of Flores.
These 3.5-foot-tall hominins – officially known as Homo floresiensis – thrived until about 50,000 years ago. Then, inexplicably, they disappeared without a trace.
Their existence only came to light in 2003 when a group of Indonesian-Australian researchers unearthed the skeleton of a female hobbit in a vast limestone cave called Liang Bua. The find was a major breakthrough in the evolutionary field.
Since the discovery, most anthropologists have been in consensus that hobbits went extinct when they vanished from Liang Bua 50,000 years ago. But now, Dr. Matt Tocheri, the co-leader of the Liang Bua excavations, and his team have uncovered evidence to the contrary.
Dr. Tocheri says that Komodo dragons, giant marabou storks, and vultures were once large species common at Liang Bua. Like the hobbits, they were probably attracted by herds of stegodons grazing outside the cave. Stegodons – an extinct elephant approximately the size of a large cow – were the main food source for these scavengers.
“The hobbits probably waited until the Komodo dragons and the scavenging birds were done picking over the stegodon corpses and then they cracked open whatever bones were left and sucked out the marrow,” he explains.
Dr. Tocheri, who is also a Lakehead University associate professor and Canada Research Chair in Human Origins, initially went to Liang Bua as a hominin expert. “Early humans, though, tend to be rare,” he says, “which meant that a lot of the time I didn’t have much to do, so I started looking at everything else being excavated. I soon noticed that rat bones made up 85-90% of all the animal bones being recovered from the cave.”
He saw the rodents as a potential trove of information about Homo floresiensis and their environment. That’s why from 2009 to 2014, Dr. Tocheri measured the hip joints of over 10,000 rats while his graduate student, Grace Veatch, measured more than 1,000 elbow joints. Their research established that diverse rat species – ranging from mouse-sized to common rabbit-sized – inhabited the cave and its surrounding area but that the frequency of the different-sized rat species varied over time.
“A striking pattern emerged that gave us new insights about the kinds of habitats that surrounded the cave at various points through time.” During the age of the hobbits, the cave was dominated by a medium-sized rat called Komodomys. This species still survives today in grassland regions, however approximately 60,000 years ago at Liang Bua, it was replaced by smaller and larger rat species more common in forested areas.
“We realized from the rats that there was a dramatic environmental change at Liang Bua around 60,000 years ago – when habitats shifted from mostly grasslands to dense forest.” It’s likely that this drove the stegodons, which prefer more open habitats, to another part of the island with more hospitable terrain.
The hobbits and other scavengers probably followed them.
If that’s the case, there’s another intriguing mystery to solve. How much longer did the hobbits survive after leaving Liang Bua and why did they die out? “I consider it most likely that modern humans were responsible for the extinction of Homo floresiensis, however, we need more evidence to prove that,” Dr. Tocheri says.
“Modern humans show up in Australia around 60,000 years ago,” he notes. To get there, they had to travel across the many Indonesian islands that lie between the Asian and Australian continents. “Despite this, the earliest evidence of modern humans within the Indonesian archipelago only dates to 40,000-45,000 years ago,” says Dr. Tocheri. “Yet, the hobbits and stegodons disappeared around that time – it’s suspicious. A lot of our work at Liang Bua is focused on refining the timeline and seeing if we can find evidence of modern humans arriving a little bit earlier.”
Even if modern humans never directly interacted with the hobbits, their behaviours could easily have led to their extinction. “Modern humans could have done enough damage to stegodon herds within one or two seasons after arriving on the island to cause the stegodon population to crash and quickly go extinct.”
In this bleak scenario, once the primary animal the hobbits had relied upon to survive for a million years was gone, their fate was sealed.