Changes in rat size reveal habitat of extinct ‘Hobbit’ humans

A study of rat body sizes shifting over time gives a glimpse into the habitat of the mysterious hominin Homo floresiensis — nicknamed the “Hobbit” due to its diminutive stature.

The research is based on an analysis of thousands of rodent bones, mainly fore- and hind-limbs, from an Indonesian cave where H. floresiensis was discovered in 2003. The results indicate that the local habitat was mostly open grasslands more than 100,000 years ago, but began shifting rapidly to a more closed environment 60,000 years ago.

“Our paper is the first that we know of to use the leg bones of rats in this way to interpret ecological change through time, and it provides new evidence for the local environment during the time of Homo Floresiensis,” says Elizabeth Grace Veatch, a PhD candidate at Emory University and a first author of the study.

H. floresiensis stood only about 3 feet 6 inches tall and was known to have lived about 190,000 to 50,000 years ago on the oceanic island of Flores in eastern Indonesia. The tiny hominin shared the island with animals that could have come from the pages of a Tolkien novel, including giant Komodo dragons, six-foot-tall storks, vultures with a six-foot wingspan, and pygmy Stegodons — herbivores that looked like small elephants with swooping, oversized tusks.

Murids, as the rat family is known, are more taxonomically diverse than any other mammal group and are found in nearly every part of the world. “They exhibit an incredible range of behaviors occupying many different ecological niches,” Veatch says. “And because small mammals are typically sensitive to ecological shifts, they can tell you a lot about what’s going on in an environment.”

While rats can adjust to new environments, the morphologies of different species tend to be adaptive to their preferred environment. For example, the habitat of the medium-sized Komodomys rintjanus, included in the study, is primarily open grasslands intermittent with patches of forest. In contrast, the tiny R. hainaldi and the giant P. armandvillei both prefer more closed or semi-closed forested habitats.

Tracking the relative abundances of the different rat species over time indicated that the local ecology was mostly open grassland 100,000 years ago, transitioning to a more-closed, forested habitat around 60,000 years ago. That is around the same time that skeletal elements belonging to Homo floresiensis, the pygmy Stegodon, giant storks, vulture and Komodo dragons disappear from Liang Bua.

“The evidence suggests that Homo floresiensis may have preferred more open habitats where they may have been a part of this scavenging guild of Stegodons, storks and vultures,” Veatch says. “We think that when the habitat changed, becoming more forested, Homo floresiensisprobably left the Liang Bua area, tracking these animals to more open habitats elsewhere on the island.”

More information: Changes in rat size reveal habitat of ‘Hobbit’ hominin

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