A unique species of Indonesian rat has given up the ability to gnaw in favour of sucking up earthworms, a team led by a Melbourne researcher has discovered.
The species of shrew rat, discovered in the rainforests of Sulawesi, have lost all molars and retain only incisors — the front four teeth, the researchers found.
Because of the unique shape of the incisors it cannot gnaw, and appears to feed exclusively on earthworms, the researchers, who include Museum Victoria’s curator of mammals Kevin Rowe, have found.
The researchers say the discovery shows how the process of evolution can lead to the reversal of previously successful traits when faced with new opportunities.
Until now all rodents were defined by their ability to gnaw and grind.
The research is published in the journal Biology Letters.Doctor Jacob Esselstyn, who worked on the research, said the lack of molars distinguished the rat from all other rodents.
"Presumably it quit using its molars a long time ago and so selection pressure which would eliminate a character that’s not necessary or inefficient to maintain would gradually eliminate that character," Dr Esselstyn from Canada’s McMaster University told AAP.
"So if it’s not using its molars to chew food anymore it would lose that function and that trait."
Stomach contents of a single specimen suggest that the species consumes only earthworms, the research shows.
"We posit that by specialising on soft-bodied prey, this species has had no need to process food by chewing, allowing its dentition to evolve for the sole purpose of procuring food," Drs Esselstyn, Rowe and a third researcher Anang Setiawan Achmad wrote in the journal.
Dr Esselstyn said the discovery of the new species show how little we know about the natural world.
"In places like Sulawesi there is obviously a lot of biodiversity that has still yet to be discovered," he said.
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